COVID-19: Effects of Environmental Conditions on the Propagation of Respiratory Droplets
- Lei ZhaoLei ZhaoDepartment of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United StatesMore by Lei Zhao,
- Yuhang QiYuhang QiDepartment of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United StatesMore by Yuhang Qi,
- Paolo Luzzatto-FegizPaolo Luzzatto-FegizDepartment of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United StatesMore by Paolo Luzzatto-Fegiz,
- Yi CuiYi CuiDepartment of Materials Science and Engineering, Stanford University, Stanford, California 94305, United StatesStanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United StatesMore by Yi Cui, and
- Yangying Zhu*Yangying Zhu*Email: [email protected]Department of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United StatesMore by Yangying Zhu
Abstract
As coronavirus disease 2019 (COVID-19) continues to spread, a detailed understanding on the transmission mechanisms is of paramount importance. The disease transmits mainly through respiratory droplets and aerosol. Although models for the evaporation and trajectory of respiratory droplets have been developed, how the environment impacts the transmission of COVID-19 is still unclear. In this study, we investigate the propagation of respiratory droplets and aerosol particles generated by speech under a wide range of temperatures (0–40 °C) and relative humidity (0–92%) conditions. We show that droplets can travel three times farther in low-temperature and high-humidity environment, whereas the number of aerosol particles increases in high-temperature and low-humidity environments. The results also underscore the importance of proper ventilation, as droplets and aerosol spread significantly farther in airstreams. This study contributes to the understanding of the environmental impact on COVID-19 transmission.
Note
Due to a produection error, this paper was published ASAP on September 15, 2020, with the wrong graphic for Figure 2. The corrected version was reposted on September 16, 2020.
Note
This article is made available via the ACS COVID-19 subset for unrestricted RESEARCH re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.
Coronavirus disease 2019 (COVID-19) is an ongoing global pandemic with more than 18 million confirmed cases and more than 700 000 deaths as of August 6, 2020.(1) The disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).(2−5) Among known transmitting pathways of SARS-CoV-2,(6,7) transmission via respiratory droplets and aerosol is believed to be a primary mode.(8,9) As influenza usually vanishes in the summer(10,11) and the SARS epidemic was effectively contained in the summer of 2003,(12) there have been earlier speculations that the current pandemic of COVID-19 may well ebb as the weather warms.(13) However, the number of confirmed cases of COVID-19 continues to rise rapidly as of August.(1) Therefore, a detailed understanding on the transmission mechanisms of SARS-CoV-2 under different environmental conditions is of paramount importance.
In general, environmental factors can impact the transmission of respiratory diseases through affecting the infectivity of the pathogens(14,15) and the propagation of respiratory droplets.(16−18) A hypothesis for the sustained high transmissibility of COVID-19 even in the summer is that SARS-CoV-2 is more persistent at high temperatures compared to influenza and SARS. A number of studies have investigated the resistance of incubated and aerosolized SARS-CoV-2 to heat and humidity.(19−21) Although more studies are needed to confirm the activity of SARS-CoV-2 in different environments, the virus can generally remain infectious from several minutes to longer than a day in various environments, much longer than the traveling time of respiratory droplets to reach another person through speech or a sneeze.(22,23) Therefore, understanding how environmental conditions impact the propagation of respiratory droplets becomes increasingly important.
The propagation of respiratory droplets plays a critical role in delivering pathogen-carrying agents to susceptible hosts. Respiratory droplets are generated by talking, coughing, and sneezing, with initial speeds ranging from ∼1 to >100 m/s.(23−25) Extensive studies have been conducted to investigate the formation,(17,18) traveling,(16−18,25,26) and infectivity(27,28) of respiratory droplets. The airborne spread of small respiratory droplets and droplet nuclei under different indoor configurations and ventilation designs have been studied to evaluate the indoor infections.(29−31) Predictions of the infection probability under certain circumstances have been reported as well.(32−34) These past studies suggest that, during the spread of respiratory droplets, both aerodynamics and evaporation determine the effectiveness of virus propagation. Although models for the evaporation and trajectory of respiratory droplets have been developed,(26,35,36) how the environmental temperature, humidity, and air velocity impact the transmission of COVID-19 is still unclear. Under certain environmental conditions, how far can the virus carriers travel on average? What fraction of droplets will turn into aerosol particles? What role do the HVAC and air conditioning systems play in virus propagation? Quantitative answers to these practical questions can provide urgently needed guidance to both policy makers and the general public, e.g., on environment-specific social distancing rules.
In this study, we investigate the influence of environmental conditions including temperature, humidity and airflow velocity, on the propagation of speech respiratory droplets. We solve the kinematic equations to analyze the transport, accumulation, and deposition of respiratory aerosol particles and calculate the spreading distance of speech droplets based on previous modeling frameworks(26,35,36) for the evaporation and trajectory of a single droplet. We evaluate the results under a wide range of temperature (0–40 °C) and relative humidity (0–92%) conditions, including weather conditions based on U.S. geographical locations. The results suggest that droplets travel farther in low-temperature and high-humidity environments, whereas the number of aerosol particles increases in high-temperature and low-humidity environments. In particular, the 6 feet of physical distance recommended by the Centers for Disease Control and Prevention (CDC) is insufficient to eliminate all possible droplet contacts in certain cold and humid environments. The risk of aerosol transmission may be increased in summer, as hot and dry environments facilitate the accumulation of PM2.5. This study highlights the need for adaptive public health precautions based on seasonal weather variations and the local environment and contributes to the understanding of the environmental impact of COVID-19 transmission.
Figure 1 presents the fate of respiratory droplets. Once released, the droplets begin to evaporate while moving under various forces (gravity, buoyancy, and air drag).(26,35,36) As a result, large droplets can directly land on another person, and small droplets dehydrate and become solid aerosol particles containing pathogens, salts, enzymes, cells, and surfactants (Figure 1). The aerosol particles defined here are different from the airborne aerosol defined by the World Health Organization (WHO),(37) which employed a straight 5 μm cutoff. Aerosol particles are capable of causing long-range infection because of their long suspension time in air.(21,38,39) On the other hand, the infection range of large droplets is limited to a relatively short distance, because the droplets can directly land on the upper body of another person before drying. Therefore, we define a critical distance Lmax as the maximum horizontal distance that all respiratory droplets can travel before they either shrink to aerosol particles or descend to the level of another person’s hands (H/2 from the ground, where H is the person’s height, Figure S5).
Figure 1
Figure 1. Transmission of COVID-19 through droplets and aerosol particles. After being exhaled by a patient, respiratory droplets with various sizes will travel and simultaneously evaporate in the ambient environment. Small-sized droplets dry immediately to form a cloud of aerosol particles. These particles will suspend in the air for a significant amount of time. Large-sized droplets can reach a limited distance and fall to the ground due to gravity. We define Lmax as the maximum horizontal distance that droplets can travel before they either become dry aerosol particles or descend below the level of another person’s hands, i.e., H/2 from the ground, where H is the height of another person.
Understanding how the environment affects transmission of COVID-19 requires predicting Lmax as well as the number of aerosol particles generated. Before a respiratory droplet evolve into aerosol particle, the evaporation dynamics and the trajectory of the droplet have been modeled by previous works,(26,35,36) based on aerodynamics, kinematics, and heat and mass transfer. These modeling frameworks are used in this study to predict Lmax and aerosolization rate φa (defined as the percentage of droplets that become aerosol particles) for a cluster of speech droplets in different environments. After respiratory droplets completely dehydrate, we solve the kinematic equations to analyze the transport, accumulation, and deposition of residual aerosol particles. The detailed model formulations, including the dynamic analysis on droplets, Brownian motion, and kinematic analysis on aerosol particles, are provided in the Supporting Information.
Key parameters considered in this study include the initial droplet velocity v0, the distribution of initial droplet size d0, environmental temperature T∞, relative humidity RH, and background air velocity Vair. The initial velocity v0 of droplets was taken as 4.1 m/s for speaking.(40) We focus on modeling speech droplets to mimic a social distancing situation where people keep a reasonable physical distance and only sneeze/cough into a tissue or their elbows. The probability distribution of initial droplet diameter d0 is derived from a previous work.(41) The initial temperature T0 of exhaled droplets was set to be 33 °C.(42) For the environment, we used Vair = 0.3 m/s in a horizontal direction as the wind speed for a typical indoor environment(43) and varied Vair from 0 to 3 m/s when analyzing the effect of wind. Respiratory droplets are assumed as a physiological saline solution (0.9% weight fraction)(26) for simplicity. Even though most buildings in the United States are maintained at 21–24 °C all year round,(44) many regions in the world do not have proper air-conditioning systems. In addition, the temperature and humidity of some industrial settings such as meat processing plants are maintained outside typical set points of residential buildings, and superspreading events have been reported therein. Therefore, we vary environmental temperature T∞ and relative humidity RH from 0 to 42 °C and 0–0.92, respectively, to include diverse situations.
The results are presented in Figure 2. For transmission via droplet contact, we plotted Lmax, as defined previously, under different temperature and humidity conditions. Figure 2a shows that droplets can travel a longer distance in humid and cool environments. Therefore, such environments require a longer physical distance. In extremely cold and humid scenarios, droplets can reach as far as 6 m. On the other hand, respiratory droplets evaporate faster in hot and dry environments (Figure S4). As those droplets sharply decrease in size, the horizontal traveling distance is reduced because of the growing damping effect of air. In most regions of Figure 2a, Lmax exceeds 1.8 m, i.e., the 6 feet of physical distance recommended by CDC. Therefore, current social distancing guidelines may be insufficient in preventing transmission via droplet contact, especially for cold and humid environments.
Figure 2
Figure 2. Effect of environmental factors on the transmission of COVID-19 via means of droplet contact and exposure to aerosol particles, respectively. (a) Maximum droplet traveling distance Lmax under different weather conditions in terms of temperature and relative humidity. Droplets can reach a longer distance in a cool and humid environment. (b) Aerosolization rate φa, defined as the percentage of respiratory droplets turning into aerosol particles that can potentially travel beyond Lmax, under different weather conditions in terms of temperature and humidity. (c) Average diameter of completely dry aerosol particles, under different weather conditions. (d) Total mass of PM2.5 floating in air that are produced by respiratory droplets per person at steady state in an enclosed space.
A quick remark regarding droplet-based transmission is that, if we consider a relaxed standard that only blocks 95% of viruses carried by respiratory droplets (excluding viruses carried by aerosol particles), this distance occurs at 1.4 m based on our results (Figure S7). Here we assumed a constant concentration of the virus in the droplets and the number of viruses is consequently proportional to the initial mass of respiratory droplets.(45) Interestingly, we find that this relaxed social distancing standard does not show an apparent dependence on the environment (see the Supporting Information). Therefore, 1.4 m may serve as a relaxed weather-independent criterion that can prevent the majority of viruses from directly landing on another person. Caution is still required as this relaxed rule does not block transmission via aerosol particles and is evaluated for speaking mode with an air velocity of 0.3 m/s. As discussed in a later section, this distance increases for an increased air velocity.
We also predict the aerosolization rate φa in different environments to evaluate the potential risk of transmission via aerosol particles. This transmission mode can be highly effective,(46) as evidenced by the increasing number of superspreading events that occurred at indoor environments. In contrast to the trend observed for Lmax, Figure 2b predicts an increasing aerosolization rate φa for hot and dry environments. The terminal sizes of these aerosol particles are in the range of 1–15 μm based on our results (Figure 2c and Figure S8). Such small particles can potentially suspend in air for hours(34,38) before settling (Figure S8) and tend to accumulate in public areas such as schools, offices, hotels, and hospitals. Therefore, the long-range infection induced by aerosol particles deserves more attention in summer, especially in dry weather.
The effectiveness of aerosol transmission also relies on the ability of aerosol particles to infiltrate respiratory tracts. Generally, small particles are able to infiltrate deeper in the respiratory tract to establish infections, as they can travel with the inhaled air current and avoid impaction within the nasal region.(27) In particular, the filtration efficiency of facial masks is also dependent on the particulate diameter and the proportion between aerosol particles and droplets.(47) Therefore, understanding the transport and size distribution of aerosol particles can provide key information to the design and fabrication of proper facial coverings under different circumstances to ensure optimal protection. We calculate the average diameter of aerosol particles floating in air under different weather conditions. The terminal size of an aerosol particle after dehydration is calculated by approximating to the volume of sodium chloride originally dissolved in the aqueous solution. The volume of viruses, estimated on the basis of the reported viral load in clinical samples(48) and the diameter of the virus,(49) is negligible compared to that of the salt contained in respiratory liquids. Therefore, we only considered the salt when modeling the size of aerosol particles (see the Supporting Information). Figure 2c demonstrates that aerosol particles have average diameters between 2 and 5 μm, and the maximum diameters are generally smaller than 10 μm, indicative of their strong ability to penetrate into the human respiratory system. The average particle diameter is increased for hot and dry weather, because more large droplets can completely evaporate because of enhanced evaporation (Figure 2b).
Because PM2.5 has been associated with a higher possibility of reaching the lung,(50) we then discuss the transport and deposition of aerosol particles classified within PM2.5 in different environment. We first computed the size-dependent suspension time ts from the following equation:
(1)where ve is the falling velocity of the aerosol particle by assuming gravity is entirely balanced by buoyancy and air drag, vt is the downward velocity of the aerosol particle at the time of drying out. If we neglect the Brownian motion, the time constant τ of the microsized droplet/particle can be written as (see the Supporting Information for details on Brownian motion and τ)
(2)where ρd is the density of the droplet, r is the droplet radius, and μa is the dynamic viscosity of air. For respiratory droplets with diameters smaller than 100 μm, the time constant τ is less than 0.05 s, indicative of a strong damping effect of air. Although large aerosol particles can be suspended in air for at least 25 min, small aerosol particles are suspended substantially longer (Figure S8b), which agrees with the previous literature.(18)
We further calculate the steady-state total mass md of PM2.5 produced by one patient that speaks continuously in an enclosed and unventilated space with a volume of Ve. The generation rate of speech droplets is from a previous study.(51) The steady state is reached when the number of aerosol particles produced from speaking is equal to the number of particles depositing onto the ground. Given the value of Ve and the average number of patients, md can be used to estimate the number density of pathogen-carrying PM2.5 in air. Figure 2d presents md in different environmental conditions. There is slightly more PM2.5 suspending in air in a hot and dry environment than in a cold and humid environment. This is mainly due to the increased suspension time in hot and dry environments as a result of the corresponding thermophysical properties of the air. Combining Figure 2b and d, the hot and dry environment not only increases the percentage of respiratory droplets turning into aerosols but also facilitates the accumulation of PM2.5 in an enclosed space. These observations raise concerns over aerosol transmission of COVID-19 in summertime, especially when the humidity is low.
Background air velocity is another environmental factor that impact the transmission of contagious diseases.(52−54) Here, we investigate the effect of the velocity of a horizontal airflow on the droplet spreading distance and aerosolization rate under a typical environment (T∞ = 23 °C, RH = 0.50). In practice, the air velocity distribution can be quite complex, and detailed CFD models are required for a more accurate prediction.(55,56) For indoor conditions, air velocity is generally maintained below 0.3 m/s for thermal comfort purposes.(57) We change the air speed from completely stagnant (Vair = 0 m/s) to Vair = 3 m/s to include diverse environmental settings. For a worst-case estimation, we consider a scenario where the airflow is always directed from a patient to another susceptible host. As shown in Figure 3, the spreading distance of droplets increases dramatically as the airflow velocity increases, which can reach 23 m at Vair = 3 m/s. In addition, the spreading distance of aerosol particles is greatly increased as well, as they are smaller in size and travel with the wind. In summary, improper airflow configurations may expand the traveling distance of pathogen-carrying droplets and aerosol particles, although introducing fresh outdoor air can effectively dilute the accumulation of infectious aerosol particles.(52) This poses stringent requirements on the meticulous design of ventilation configurations in nonhospital facilities, so as to curb the transmission of COVID-19.
Figure 3
Figure 3. Effect of a horizontal, constant background airflow. Droplet spreading distance Lmax as a function of a horizontal, constant air speed.
To help evaluate the risk of infections in different regions across the United States, we computed Lmax and φa based on the average weather conditions of each state in August,(58) and the results are shown in Figure 4 a and b. The weather data we collected are a monthly average over day and night as well as rural and urban regions. Figure 4 shows that, the inland regions are more vulnerable to aerosolization of viruses and the coastal regions should be cautious of droplet-based infections. California, on average, exhibits a higher risk of droplet spreading but a lower risk of infection induced by aerosol particles (Figure 4a and b). However, within the state of California, strong variations exist as shown in Figure 4c and d. Note that Figure 4c and d was plotted using the average temperature and relative humidity in the afternoon of August.(58) We also analyzed Lmax and φa in major U.S. cities in both summer (August) and winter (December) climates, as shown in Figure 4e and f. Compared to summer, there is a higher chance of droplet-based infections in winter, whereas the aerosolization rate merely changes. Considering the extreme stability of SARS-CoV-2 at low temperature,(19) a recurrent wintertime outbreak of COVID-19 is entirely probable.
Figure 4
Figure 4. Geographical distribution of droplet spreading distance and aerosolization rate across the United States. (a) Spreading distance Lmax and (b) aerosolization rate φa in each U.S. state based on its monthly average weather condition in August. County-by-county distribution of (c) spreading distance Lmax and (d) aerosolization rate φa in California based on their monthly average weather conditions for August afternoons. (e) Safe distance Lmax and (f) aerosolization rate φa in major U.S. cities in summer and winter. Indoor wind speed is assumed (Vair = 0.3 m/s).
To summarize, we investigate the effect of environmental temperature, relative humidity, and airflow velocity on the propagation of respiratory droplets and accumulation of aerosol particles in order to elucidate environmental impacts on the transmission of COVID-19. We show that droplets travel farther in low-temperature and high-humidity environments, whereas the number of aerosol particles increases in high-temperature and low-humidity environments. The current social distancing standard is insufficient in many situations, as droplets may reach as far as 6 m in extremely cold and humid environments. Alternatively, a relaxed standard of 1.4 m is able to block 95% of the viruses carried by respiratory droplets (excluding that carried by aerosol particles) and shows negligible variation over different environmental conditions. Improper airflow can dramatically increase the traveling distance of both droplets and aerosol particles and consequently increases the risk of COVID-19 transmission. Although particulate diameter differs over different environmental settings, proper and adaptive face-coverings based on the aerosolization of respiratory droplets is recommended.(59−61) These findings suggest that adaptive public health measures should be taken in accordance with seasonal weather variations and local environments. The insights gained from this study may shed light on the course of development of the current pandemic, when combined with systematic epidemiological studies.
ARTICLE SECTIONS
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03331.
Detailed information about the modeling framework, analysis on the Brownian motion, size distribution and evaporation dynamics of respiratory droplets, distance-dependent viral load distribution, and calculation of suspending aerosol particles (PDF)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.
Author Information
ARTICLE SECTIONS
- Lei Zhao - Department of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United States;
http://orcid.org/0000-0002-1743-2606 - Yi Cui - Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States; Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States;http://orcid.org/0000-0002-6103-6352
The authors declare the following competing financial interest(s): Y.C. is a cofounder and shareholder of the company 4C Air, Inc. He is a co-inventor on patent PCT/US2015/065608.
Acknowledgments
ARTICLE SECTIONS
This work is supported by the startup funding from University of California, Santa Barbara. We acknowledge synergies made possible by a UCSB VCR COVID-19 Seed Grant to P.L.-F.
References
ARTICLE SECTIONS
This article references 61 other publications.
- 1Dong, E.; Du, H.; Gardner, L. An Interactive Web-Based Dashboard to Track COVID-19 in Real Time. Lancet Infect. Dis. 2020, 20 (5), 533– 534, DOI: 10.1016/S1473-3099(20)30120-1[Crossref], [PubMed], [CAS], Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksVaisbs%253D&md5=7f528642a4d2b2fcc3575e37085819a8An interactive web-based dashboard to track COVID-19 in real timeDong, Ensheng; Du, Hongru; Gardner, LaurenLancet Infectious Diseases (2020), 20 (5), 533-534CODEN: LIDABP; ISSN:1473-3099. (Elsevier Ltd.)The authors describe the development of an online interactive dashboard, hosted by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University, Baltimore, MD, USA, to visualize and track reported cases of coronavirus disease 2019 (COVID-19) in real time. The dashboard, first shared publicly on Jan 22, illustrates the location and no. of confirmed COVID-19 cases, deaths, and recoveries for all affected countries. It was developed to provide researchers, public health authorities, and the general public with a user-friendly tool to track the outbreak as it unfolds. All data collected and displayed are made freely available, initially through Google Sheets and now through a GitHub repository, along with the feature layers of the dashboard, which are now included in the Esri Living Atlas.
- 2Zhou, P.; Yang, X.-L.; Wang, X.-G.; Hu, B.; Zhang, L.; Zhang, W.; Si, H.-R.; Zhu, Y.; Li, B.; Huang, C.-L.; others A Pneumonia Outbreak Associated with a New Coronavirus of Probable Bat Origin. Nature 2020, 579 (7798), 270– 273, DOI: 10.1038/s41586-020-2012-7[Crossref], [PubMed], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksFKlsLg%253D&md5=236f17d4d3c7978d72513e5e0258f1b3A pneumonia outbreak associated with a new coronavirus of probable bat originZhou, Peng; Yang, Xing-Lou; Wang, Xian-Guang; Hu, Ben; Zhang, Lei; Zhang, Wei; Si, Hao-Rui; Zhu, Yan; Li, Bei; Huang, Chao-Lin; Chen, Hui-Dong; Chen, Jing; Luo, Yun; Guo, Hua; Jiang, Ren-Di; Liu, Mei-Qin; Chen, Ying; Shen, Xu-Rui; Wang, Xi; Zheng, Xiao-Shuang; Zhao, Kai; Chen, Quan-Jiao; Deng, Fei; Liu, Lin-Lin; Yan, Bing; Zhan, Fa-Xian; Wang, Yan-Yi; Xiao, Geng-Fu; Shi, Zheng-LiNature (London, United Kingdom) (2020), 579 (7798), 270-273CODEN: NATUAS; ISSN:0028-0836. (Nature Research)Abstr.: Since the outbreak of severe acute respiratory syndrome (SARS) 18 years ago, a large no. of SARS-related coronaviruses (SARSr-CoVs) have been discovered in their natural reservoir host, bats1-4. Previous studies have shown that some bat SARSr-CoVs have the potential to infect humans5-7. Here we report the identification and characterization of a new coronavirus (2019-nCoV), which caused an epidemic of acute respiratory syndrome in humans in Wuhan, China. The epidemic, which started on 12 Dec. 2019, had caused 2,794 lab.-confirmed infections including 80 deaths by 26 Jan. 2020. Full-length genome sequences were obtained from five patients at an early stage of the outbreak. The sequences are almost identical and share 79.6% sequence identity to SARS-CoV. Furthermore, we show that 2019-nCoV is 96% identical at the whole-genome level to a bat coronavirus. Pairwise protein sequence anal. of seven conserved non-structural proteins domains show that this virus belongs to the species of SARSr-CoV. In addn., 2019-nCoV virus isolated from the bronchoalveolar lavage fluid of a critically ill patient could be neutralized by sera from several patients. Notably, we confirmed that 2019-nCoV uses the same cell entry receptor-angiotensin converting enzyme II (ACE2)-as SARS-CoV.
- 3Wu, F.; Zhao, S.; Yu, B.; Chen, Y.-M.; Wang, W.; Song, Z.-G.; Hu, Y.; Tao, Z.-W.; Tian, J.-H.; Pei, Y.-Y.; others A New Coronavirus Associated with Human Respiratory Disease in China. Nature 2020, 579 (7798), 265– 269, DOI: 10.1038/s41586-020-2008-3[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksFKlsLc%253D&md5=0163a684829e880a0c3347e19f0ce52aA new coronavirus associated with human respiratory disease in ChinaWu, Fan; Zhao, Su; Yu, Bin; Chen, Yan-Mei; Wang, Wen; Song, Zhi-Gang; Hu, Yi; Tao, Zhao-Wu; Tian, Jun-Hua; Pei, Yuan-Yuan; Yuan, Ming-Li; Zhang, Yu-Ling; Dai, Fa-Hui; Liu, Yi; Wang, Qi-Min; Zheng, Jiao-Jiao; Xu, Lin; Holmes, Edward C.; Zhang, Yong-ZhenNature (London, United Kingdom) (2020), 579 (7798), 265-269CODEN: NATUAS; ISSN:0028-0836. (Nature Research)Emerging infectious diseases, such as severe acute respiratory syndrome (SARS) and Zika virus disease, present a major threat to public health. Despite intense research efforts, how, when and where new diseases appear are still a source of considerable uncertainty. A severe respiratory disease was recently reported in Wuhan, Hubei province, China. As of 25 Jan. 2020, at least 1,975 cases had been reported since the first patient was hospitalized on 12 Dec. 2019. Epidemiol. investigations have suggested that the outbreak was assocd. with a seafood market in Wuhan. Here we study a single patient who was a worker at the market and who was admitted to the Central Hospital of Wuhan on 26 Dec. 2019 while experiencing a severe respiratory syndrome that included fever, dizziness and a cough. Metagenomic RNA sequencing of a sample of bronchoalveolar lavage fluid from the patient identified a new RNA virus strain from the family Coronaviridae, which is designated here 'WH-Human 1' coronavirus (and has also been referred to as '2019-nCoV'). Phylogenetic anal. of the complete viral genome (29,903 nucleotides) revealed that the virus was most closely related (89.1% nucleotide similarity) to a group of SARS-like coronaviruses (genus Betacoronavirus, subgenus Sarbecovirus) that had previously been found in bats in China. This outbreak highlights the ongoing ability of viral spill-over from animals to cause severe disease in humans.
- 4Guan, W.; Ni, Z.; Hu, Y.; Liang, W.; Ou, C.; He, J.; Liu, L.; Shan, H.; Lei, C.; Hui, D. S.; others Clinical Characteristics of Coronavirus Disease 2019 in China. N. Engl. J. Med. 2020, 382 (18), 1708– 1720, DOI: 10.1056/NEJMoa2002032[Crossref], [PubMed], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXovVSjsb8%253D&md5=db6fa99e647c6ba6862ad1d795118ab1Clinical characteristics of coronavirus disease 2019 in ChinaGuan, W.; Ni, Z.; Hu, Yu; Liang, W.; Ou, C.; He, J.; Liu, L.; Shan, H.; Lei, C.; Hui, D. S. C.; Du, B.; Li, L.; Zeng, G.; Yuen, K.-Y.; Chen, R.; Tang, C.; Wang, T.; Chen, P.; Xiang, J.; Li, S.; Wang, Jin-lin; Liang, Z.; Peng, Y.; Wei, L.; Liu, Y.; Hu, Ya-hua; Peng, P.; Wang, Jian-ming; Liu, J.; Chen, Z.; Li, G.; Zheng, Z.; Qiu, S.; Luo, J.; Ye, C.; Zhu, S.; Zhong, N.New England Journal of Medicine (2020), 382 (18), 1708-1720CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)Background: Since Dec. 2019, when coronavirus disease 2019 (Covid-19) emerged in Wuhan city and rapidly spread throughout China, data have been needed on the clin. characteristics of the affected patients. Methods: We extd. data regarding 1099 patients with lab.-confirmed Covid-19 from 552 hospitals in 30 provinces, autonomous regions, and municipalities in mainland China through Jan. 29, 2020. The primary composite end point was admission to an intensive care unit (ICU), the use of mech. ventilation, or death. results The median age of the patients was 47 years; 41.9% of the patients were female. The primary composite end point occurred in 67 patients (6.1%), including 5.0% who were admitted to the ICU, 2.3% who underwent invasive mech. ventilation, and 1.4% who died. Only 1.9% of the patients had a history of direct contact with wildlife. Among nonresidents of Wuhan, 72.3% had contact with residents of Wuhan, including 31.3% who had visited the city. The most common symptoms were fever (43.8% on admission and 88.7% during hospitalization) and cough (67.8%). Diarrhea was uncommon (3.8%). The median incubation period was 4 days (interquartile range, 2 to 7). On admission, ground-glass opacity was the most common radiol. finding on chest computed tomog. (CT) (56.4%). No radiog. or CT abnormality was found in 157 of 877 patients (17.9%) with nonsevere disease and in 5 of 173 patients (2.9%) with severe disease. Lymphocytopenia was present in 83.2% of the patients on admission.hCt scan. Conclusions: During the first 2 mo of the current outbreak, Covid-19 spread rapidly throughout China and caused varying degrees of illness. Patients often presented without fever, and many did not have abnormal radiol. findings.
- 5Letko, M.; Marzi, A.; Munster, V. Functional Assessment of Cell Entry and Receptor Usage for SARS-CoV-2 and Other Lineage B Betacoronaviruses. Nat. Microbiol. 2020, 5 (4), 562– 569, DOI: 10.1038/s41564-020-0688-y[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjvFyitL0%253D&md5=98931812734d0f364d4d0c5f88a9d165Functional assessment of cell entry and receptor usage for SARS-CoV-2 and other lineage B betacoronavirusesLetko, Michael; Marzi, Andrea; Munster, VincentNature Microbiology (2020), 5 (4), 562-569CODEN: NMAICH; ISSN:2058-5276. (Nature Research)Over the past 20 years, several coronaviruses have crossed the species barrier into humans, causing outbreaks of severe, and often fatal, respiratory illness. Since SARS-CoV was first identified in animal markets, global viromics projects have discovered thousands of coronavirus sequences in diverse animals and geog. regions. Unfortunately, there are few tools available to functionally test these viruses for their ability to infect humans, which has severely hampered efforts to predict the next zoonotic viral outbreak. Here, we developed an approach to rapidly screen lineage B betacoronaviruses, such as SARS-CoV and the recent SARS-CoV-2, for receptor usage and their ability to infect cell types from different species. We show that host protease processing during viral entry is a significant barrier for several lineage B viruses and that bypassing this barrier allows several lineage B viruses to enter human cells through an unknown receptor. We also demonstrate how different lineage B viruses can recombine to gain entry into human cells, and confirm that human ACE2 is the receptor for the recently emerging SARS-CoV-2.
- 6Leung, K.; Wu, J. T.; Liu, D.; Leung, G. M. First-Wave COVID-19 Transmissibility and Severity in China Outside Hubei after Control Measures, and Second-Wave Scenario Planning: A Modelling Impact Assessment. Lancet 2020, 395 (10233), 1382– 1393, DOI: 10.1016/S0140-6736(20)30746-7[Crossref], [PubMed], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntFSmurg%253D&md5=424307813486dc45252b6f235fd9de52First-wave COVID-19 transmissibility and severity in China outside Hubei after control measures, and second-wave scenario planning: a modelling impact assessmentLeung, Kathy; Wu, Joseph T.; Liu, Di; Leung, Gabriel M.Lancet (2020), 395 (10233), 1382-1393CODEN: LANCAO; ISSN:0140-6736. (Elsevier Ltd.)As of March 18, 2020, 13 415 confirmed cases and 120 deaths related to coronavirus disease 2019 (COVID-19) in mainland China, outside Hubei province-the epicentre of the outbreak-had been reported. Since late Jan., massive public health interventions have been implemented nationwide to contain the outbreak. We provide an impact assessment of the transmissibility and severity of COVID-19 during the first wave in mainland Chinese locations outside Hubei. We estd. the instantaneous reprodn. no. (Rt) of COVID-19 in Beijing, Shanghai, Shenzhen, Wenzhou, and the ten Chinese provinces that had the highest no. of confirmed COVID-19 cases; and the confirmed case-fatality risk (cCFR) in Beijing, Shanghai, Shenzhen, and Wenzhou, and all 31 Chinese provinces. We used a susceptible-infectious-recovered model to show the potential effects of relaxing containment measures after the first wave of infection, in anticipation of a possible second wave. In all selected cities and provinces, the Rt decreased substantially since Jan 23, when control measures were implemented, and have since remained below 1. The cCFR outside Hubei was 0·98% (95% CI 0·82-1·16), which was almost five times lower than that in Hubei (5·91%, 5·73-6·09). Relaxing the interventions (resulting in Rt >1) when the epidemic size was still small would increase the cumulative case count exponentially as a function of relaxation duration, even if aggressive interventions could subsequently push disease prevalence back to the baseline level. The first wave of COVID-19 outside of Hubei has abated because of aggressive non-pharmaceutical interventions. However, given the substantial risk of viral reintroduction, particularly from overseas importation, close monitoring of Rt and cCFR is needed to inform strategies against a potential second wave to achieve an optimal balance between health and economic protection. Health and Medical Research Fund, Hong Kong, China.
- 7Arons, M. M.; Hatfield, K. M.; Reddy, S. C. Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility. N. Engl. J. Med. 2020, 382, 2081– 2090, DOI: 10.1056/NEJMoa2008457[Crossref], [PubMed], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVGqsrfE&md5=2b91e64e3768320452df1608735568b5Presymptomatic SARS-CoV-2 infections and transmission in a skilled nursing facilityArons, M. M.; Hatfield, K. M.; Reddy, S. C.; Kimball, A.; James, A.; Jacobs, J. R.; Taylor, J.; Spicer, K.; Bardossy, A. C.; Oakley, L. P.; Tanwar, S.; Dyal, J. W.; Harney, J.; Chisty, Z.; Bell, J. M.; Methner, M.; Paul, P.; Carlson, C. M.; McLaughlin, H. P.; Thornburg, N.; Tong, S.; Tamin, A.; Tao, Y.; Uehara, A.; Harcourt, J.; Clark, S.; Brostrom-Smith, C.; Page, L. C.; Kay, M.; Lewis, J.; Montgomery, P.; Stone, N. D.; Clark, T. A.; Honein, M. A.; Duchin, J. S.; Jernigan, J. A.New England Journal of Medicine (2020), 382 (22), 2081-2090CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can spread rapidly within skilled nursing facilities. After identification of a case of Covid-19 in a skilled nursing facility, we assessed transmission and evaluated the adequacy of symptom-based screening to identify infections in residents. Methods: We conducted two serial point-prevalence surveys, 1 wk apart, in which assenting residents of the facility underwent nasopharyngeal and oropharyngeal testing for SARS-CoV-2, including real-time reverse-transcriptase polymerase chain reaction (rRT-PCR), viral culture, and sequencing. Symptoms that had been present during the preceding 14 days were recorded. Asymptomatic residents who tested pos. were reassessed 7 days later. Residents with SARS-CoV-2 infection were categorized as symptomatic with typical symptoms (fever, cough, or shortness of breath), symptomatic with only atypical symptoms, presymptomatic, or asymptomatic. Results: Twenty-three days after the first pos. test result in a resident at this skilled nursing facility, 57 of 89 residents (64%) tested pos. for SARS-CoV-2. Among 76 residents who participated in point-prevalence surveys, 48 (63%) tested pos. Of these 48 residents, 27 (56%) were asymptomatic at the time of testing; 24 subsequently developed symptoms (median time to onset, 4 days). Samples from these 24 presymptomatic residents had a median rRT-PCR cycle threshold value of 23.1, and viable virus was recovered from 17 residents. As of Apr. 3, of the 57 residents with SARS-CoV-2 infection, 11 had been hospitalized (3 in the intensive care unit) and 15 had died (mortality, 26%). Of the 34 residents whose specimens were sequenced, 27 (79%) had sequences that fit into two clusters with a difference of one nucleotide. Conclusions: Rapid and widespread transmission of SARS-CoV-2 was demonstrated in this skilled nursing facility. More than half of residents with pos. test results were asymptomatic at the time of testing and most likely contributed to transmission. Infection-control strategies focused solely on symptomatic residents were not sufficient to prevent transmission after SARS-CoV-2 introduction into this facility.
- 8Booth, T. F.; Kournikakis, B.; Bastien, N.; Ho, J.; Kobasa, D.; Stadnyk, L.; Li, Y.; Spence, M.; Paton, S.; Henry, B. Detection of Airborne Severe Acute Respiratory Syndrome (SARS) Coronavirus and Environmental Contamination in SARS Outbreak Units. J. Infect. Dis. 2005, 191 (9), 1472– 1477, DOI: 10.1086/429634[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2M7ns1Gqug%253D%253D&md5=6314670743c6b810394a8a6073242bc0Detection of airborne severe acute respiratory syndrome (SARS) coronavirus and environmental contamination in SARS outbreak unitsBooth Timothy F; Kournikakis Bill; Bastien Nathalie; Ho Jim; Kobasa Darwyn; Stadnyk Laurie; Li Yan; Spence Mel; Paton Shirley; Henry Bonnie; Mederski Barbara; White Diane; Low Donald E; McGeer Allison; Simor Andrew; Vearncombe Mary; Downey James; Jamieson Frances B; Tang Patrick; Plummer FrankThe Journal of infectious diseases (2005), 191 (9), 1472-7 ISSN:0022-1899.Severe acute respiratory syndrome (SARS) is characterized by a risk of nosocomial transmission; however, the risk of airborne transmission of SARS is unknown. During the Toronto outbreaks of SARS, we investigated environmental contamination in SARS units, by employing novel air sampling and conventional surface swabbing. Two polymerase chain reaction (PCR)-positive air samples were obtained from a room occupied by a patient with SARS, indicating the presence of the virus in the air of the room. In addition, several PCR-positive swab samples were recovered from frequently touched surfaces in rooms occupied by patients with SARS (a bed table and a television remote control) and in a nurses' station used by staff (a medication refrigerator door). These data provide the first experimental confirmation of viral aerosol generation by a patient with SARS, indicating the possibility of airborne droplet transmission, which emphasizes the need for adequate respiratory protection, as well as for strict surface hygiene practices.
- 9Herfst, S.; Schrauwen, E. J.; Linster, M. Airborne Transmission of Influenza A/H5N1 Virus between Ferrets. Science 2012, 336 (6088), 1534– 1541, DOI: 10.1126/science.1213362[Crossref], [PubMed], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xoslaksbw%253D&md5=19a11c8baf401ca29fade4b35b1c582dAirborne transmission of influenza A/H5N1 virus between ferretsHerfst, Sander; Schrauwen, Eefje J. A.; Linster, Martin; Chutinimitkul, Salin; de Wit, Emmie; Munster, Vincent J.; Sorrell, Erin M.; Bestebroer, Theo M.; Burke, David F.; Smith, Derek J.; Rimmelzwaan, Guus F.; Osterhaus, Albert D. M. E.; Fouchier, Ron A. M.Science (Washington, DC, United States) (2012), 336 (6088), 1534-1541CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Highly pathogenic avian influenza A/H5N1 virus can cause morbidity and mortality in humans but thus far has not acquired the ability to be transmitted by aerosol or respiratory droplet ("airborne transmission") between humans. To address the concern that the virus could acquire this ability under natural conditions, we genetically modified A/H5N1 virus by site-directed mutagenesis and subsequent serial passage in ferrets. The genetically modified A/H5N1 virus acquired mutations during passage in ferrets, ultimately becoming airborne transmissible in ferrets. None of the recipient ferrets died after airborne infection with the mutant A/H5N1 viruses. Four amino acid substitutions in the host receptor-binding protein hemagglutinin, and one in the polymerase complex protein basic polymerase 2, were consistently present in airborne-transmitted viruses. The transmissible viruses were sensitive to the antiviral drug oseltamivir and reacted well with antisera raised against H5 influenza vaccine strains. Thus, avian A/H5N1 influenza viruses can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host and therefore constitute a risk for human pandemic influenza.
- 10Ye, C.; Zhu, W.; Yu, J. Understanding the complex seasonality of seasonal influenza A and B virus transmission: Evidence from six years of surveillance data in Shanghai, China. Int. J. Infect. Dis. 2019, 81, 57– 65, DOI: 10.1016/j.ijid.2019.01.027[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3cjlsFKgsw%253D%253D&md5=6f7da0e513d37f909fbc8c826022559aUnderstanding the complex seasonality of seasonal influenza A and B virus transmission: Evidence from six years of surveillance data in Shanghai, ChinaYe Chuchu; Zhu Weiping; Wang Yuanping; Gu Huozheng; Zou Wenwei; Yu Jianxing; Li Zhongjie; Zhang Yuzhou; Hao Lipeng; Hu WenbiaoInternational journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases (2019), 81 (), 57-65 ISSN:.OBJECTIVES: Understanding the complexity of influenza subtype seasonality is critical to promoting a suitable vaccination program. The aim of this study was to identify and compare the seasonality and epidemiological features of seasonal influenza subtypes after the 2009 A/H1N1 pandemic and to lay a foundation for further investigation into the social and environmental factors affecting seasonal influenza virus transmission. METHODS: Influenza-like illness (ILI) case surveillance was conducted in two sentinel hospitals in Pudong New Area, Shanghai between 2012 and 2018. Weekly data on ILI cases were analyzed. A time-series seasonal decomposition analysis was used to reveal the seasonality of influenza and epidemiological features among different subtypes. RESULTS: In total, 10977 ILI patients were enrolled of whom 2385 (21.7%) had laboratory-confirmed influenza. Compared to influenza A (16.3%), influenza B (5.4%) was less frequently detected among the ILI patients (p<0.001). Semiannual epidemic peaks were identified in four of the years during the 6-year study period, while only one annual epidemic peak was found in the other two years. An epidemic peak occurred in each winter season, and a secondary peak also occasionally occurred in summer or spring. A/H3N2 predominated in both summer and winter, while A/H1N1, B/Yamagata, and B/Victoria circulated almost exclusively in winter or spring. Two lineages of influenza B seemed to predominate in alternating years. CONCLUSIONS: This study highlights the complexity of seasonal influenza virus activity in a subtropical region of China, presenting both semiannual and annual epidemic peaks in different years. The results of this study may provide further insight into possible improvements in the timing of influenza vaccination in Shanghai, China.
- 11Lofgren, E.; Fefferman, N. H.; Naumov, Y. N.; Gorski, J.; Naumova, E. N. Influenza seasonality: underlying causes and modeling theories. J. Virol. 2007, 81 (11), 5429– 5436, DOI: 10.1128/JVI.01680-06[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmtFGlt7g%253D&md5=4df6ce502bada95908fcc738c9f24921Influenza seasonality: underlying causes and modeling theoriesLofgren, Eric; Fefferman, N. H.; Naumov, Y. N.; Gorski, J.; Naumova, E. N.Journal of Virology (2007), 81 (11), 5429-5436CODEN: JOVIAM; ISSN:0022-538X. (American Society for Microbiology)There is no expanded citation for this reference.
- 12Likhacheva, A. SARS Revisited. AMA J. Ethics 2006, 8 (4), 219– 222
- 13Lipsitch, M. Seasonality of SARS-CoV-2: Will COVID-19 go away on its own in warmer weather? https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-own-in-warmer-weather/ (accessed 2020-05-03).Google ScholarThere is no corresponding record for this reference.
- 14Lowen, A. C.; Steel, J. Roles of humidity and temperature in shaping influenza seasonality. J. Virol. 2014, 88 (14), 7692– 7695, DOI: 10.1128/JVI.03544-13[Crossref], [PubMed], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVKjtbbK&md5=f3c79f190ec631fddb3b7d788cf7f4f9Roles of humidity and temperature in shaping influenza seasonalityLowen, Anice C.; Steel, JohnJournal of Virology (2014), 88 (14), 7692-7695, 5 pp.CODEN: JOVIAM; ISSN:1098-5514. (American Society for Microbiology)Exptl. studies in guinea pigs demonstrated that influenza virus transmission is strongly modulated by temp. and humidity. A no. of epidemiol. studies have followed up on these findings and revealed robust assocns. between influenza incidence in temperate regions and local conditions of humidity and temp., offering a long-awaited explanation for the wintertime seasonality of influenza in these locales. Despite recent progress, important questions remain as to the mechanism(s) by which humidity and/or temp. affects transmission.
- 15Chan, K. H.; Peiris, J. S. M.; Lam, S. Y.; Poon, L. L. M.; Yuen, K. Y.; Seto, W. H. The effects of temperature and relative humidity on the viability of the SARS coronavirus. Adv. Virol. 2011, 2011 (734690), 1– 7, DOI: 10.1155/2011/734690
- 16Bourouiba, L. Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19. JAMA 2020, 323 (18), 1837– 1838, DOI: 10.1001/jama.2020.4756[Crossref], [PubMed], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383nslKqtg%253D%253D&md5=e240ace69fbf2eebd3446aa623e9c556Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19Bourouiba LydiaJAMA (2020), 323 (18), 1837-1838 ISSN:.There is no expanded citation for this reference.
- 17Mittal, R.; Ni, R.; Seo, J.-H. The Flow Physics of COVID-19. J. Fluid Mech. 2020, 894, 894, DOI: 10.1017/jfm.2020.330
- 18Scharfman, B. E.; Techet, A. H.; Bush, J. W. M.; Bourouiba, L. Visualization of Sneeze Ejecta: Steps of Fluid Fragmentation Leading to Respiratory Droplets. Exp. Fluids 2016, 57 (2), 24, DOI: 10.1007/s00348-015-2078-4[Crossref], [PubMed], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383ns1Olsg%253D%253D&md5=d1ff8e6d9059aec4895a3799c47b0959Visualization of sneeze ejecta: steps of fluid fragmentation leading to respiratory dropletsScharfman B E; Techet A H; Bush J W M; Bourouiba LExperiments in fluids (2016), 57 (2), 24 ISSN:0723-4864.Coughs and sneezes feature turbulent, multiphase flows that may contain pathogen-bearing droplets of mucosalivary fluid. As such, they can contribute to the spread of numerous infectious diseases, including influenza and SARS. The range of contamination of the droplets is largely determined by their size. However, major uncertainties on the drop size distributions persist. Here, we report direct observation of the physical mechanisms of droplet formation at the exit of the mouth during sneezing. Specifically, we use high-speed imaging to directly examine the fluid fragmentation at the exit of the mouths of healthy subjects. We reveal for the first time that the breakup of the fluid into droplets continues to occur outside of the respiratory tract during violent exhalations. We show that such breakup involves a complex cascade of events from sheets, to bag bursts, to ligaments, which finally break into droplets. Finally, we reveal that the viscoelasticity of the mucosalivary fluid plays an important role in delaying fragmentation by causing the merger of the droplet precursors that form along stretched filaments; thereby affecting the final drop size distribution farther downstream.
- 19Chin, A.; Chu, J.; Perera, M.; Hui, K.; Yen, H.-L.; Chan, M.; Peiris, M.; Poon, L. Stability of SARS-CoV-2 in Different Environmental Conditions. Lancet Microbe 2020, 1 (1), e10 DOI: 10.1016/S2666-5247(20)30003-3[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXit1Kms7%252FJ&md5=933fd5dff634c6f2bd88095b1ef316fcStability of SARS-CoV-2 in different environmental conditionsChin, Alex W. H.; Chu, Julie T. S.; Perera, Mahen R. A.; Hui, Kenrie P. Y.; Yen, Hui-Ling; Chan, Michael C. W.; Peiris, Malik; Poon, Leo L. M.Lancet Microbe (2020), 1 (1), e10CODEN: LMAIAR; ISSN:2666-5247. (Elsevier Ltd.)There is no expanded citation for this reference.
- 20van Doremalen, N.; Bushmaker, T.; Morris, D. H.; Holbrook, M. G.; Gamble, A.; Williamson, B. N.; Tamin, A.; Harcourt, J. L.; Thornburg, N. J.; Gerber, S. I. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N. Engl. J. Med. 2020, 382 (16), 1564– 1567, DOI: 10.1056/NEJMc2004973[Crossref], [PubMed], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383ksVKktw%253D%253D&md5=9803ae46c83b19c312f0d810c975378eAerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1van Doremalen Neeltje; Bushmaker Trenton; Holbrook Myndi G; Williamson Brandi N; de Wit Emmie; Munster Vincent J; Morris Dylan H; Gamble Amandine; Tamin Azaibi; Harcourt Jennifer L; Thornburg Natalie J; Gerber Susan I; Lloyd-Smith James OThe New England journal of medicine (2020), 382 (16), 1564-1567 ISSN:.There is no expanded citation for this reference.
- 21Fears, A. C.; Klimstra, W. B.; Duprex, P.; Hartman, A. Comparative Dynamic Aerosol Efficiencies of Three Emergent Coronaviruses and the Unusual Persistence of SARS-CoV-2 in Aerosol Suspensions. medRxiv, 2020, 2020.04.13.20063784. DOI: 10.1101/2020.04.13.20063784v1 (accessed 2020-05-04).
- 22Stadnytskyi, V.; Bax, C. E.; Bax, A.; Anfinrud, P. The Airborne Lifetime of Small Speech Droplets and Their Potential Importance in SARS-CoV-2 Transmission. Proc. Natl. Acad. Sci. U. S. A. 2020, 117 (22), 11875– 11877, DOI: 10.1073/pnas.2006874117[Crossref], [PubMed], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtlSltrzI&md5=e553c69851fc1afc32e617ccd7be00f9The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmissionStadnytskyi, Valentyn; Bax, Christina E.; Bax, AdriaanProceedings of the National Academy of Sciences of the United States of America (2020), 117 (22), 11875-11877CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly considered to be a likely mode of disease transmission. Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per s. In a closed, stagnant air environment, they disappear from the window of view with time consts. in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4μm diam., or 12- to 21-μm droplets prior to dehydration. These observations confirm that there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.
- 23Xie, X.; Li, Y.; Sun, H.; Liu, L. Exhaled Droplets Due to Talking and Coughing. J. R. Soc., Interface 2009, 6, S703– S714, DOI: 10.1098/rsif.2009.0388.focus
- 24Cole, E. C.; Cook, C. E. Characterization of Infectious Aerosols in Health Care Facilities: An Aid to Effective Engineering Controls and Preventive Strategies. Am. J. Infect. Control 1998, 26 (4), 453– 464, DOI: 10.1016/S0196-6553(98)70046-X[Crossref], [PubMed], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADyaK1czovVaqsg%253D%253D&md5=9cab0801c49e70f15609fa166b3640d6Characterization of infectious aerosols in health care facilities: an aid to effective engineering controls and preventive strategiesCole E C; Cook C EAmerican journal of infection control (1998), 26 (4), 453-64 ISSN:0196-6553.Assessment of strategies for engineering controls for the prevention of airborne infectious disease transmission to patients and to health care and related workers requires consideration of the factors relevant to aerosol characterization. These factors include aerosol generation, particle size and concentrations, organism viability, infectivity and virulence, airflow and climate, and environmental sampling and analysis. The major focus on attention to engineering controls comes from recent increases in tuberculosis, particularly the multidrug-resistant varieties in the general hospital population, the severely immunocompromised, and those in at-risk and confined environments such as prisons, long-term care facilities, and shelters for the homeless. Many workers are in close contact with persons who have active, undiagnosed, or insufficiently treated tuberculosis. Additionally, patients and health care workers may be exposed to a variety of pathogenic human viruses, opportunistic fungi, and bacteria. This report therefore focuses on the nature of infectious aerosol transmission in an attempt to determine which factors can be systematically addressed to result in proven, applied engineering approaches to the control of infectious aerosols in hospital and health care facility environments. The infectious aerosols of consideration are those that are generated as particles of respirable size by both human and environmental sources and that have the capability of remaining viable and airborne for extended periods in the indoor environment. This definition precludes skin and mucous membrane exposures occurring from splashes (rather than true aerosols) of blood or body fluids containing infectious disease agents. There are no epidemiologic or laboratory studies documenting the transmission of bloodborne virus by way of aerosols.
- 25Chao, C. Y. H.; Wan, M. P.; Morawska, L.; Johnson, G. R.; Ristovski, Z. D.; Hargreaves, M.; Mengersen, K.; Corbett, S.; Li, Y.; Xie, X.; Katoshevski, D. Characterization of expiration air jets and droplet size distributions immediately at the mouth opening. J. Aerosol Sci. 2009, 40 (2), 122– 133, DOI: 10.1016/j.jaerosci.2008.10.003[Crossref], [PubMed], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFSns7Y%253D&md5=6f35010e4b5a1f48b02026c888d637a4Characterization of expiration air jets and droplet size distributions immediately at the mouth openingChao, C. Y. H.; Wan, M. P.; Morawska, L.; Johnson, G. R.; Ristovski, Z. D.; Hargreaves, M.; Mengersen, K.; Corbett, S.; Li, Y.; Xie, X.; Katoshevski, D.Journal of Aerosol Science (2009), 40 (2), 122-133CODEN: JALSB7; ISSN:0021-8502. (Elsevier Ltd.)Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The av. expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the exptl. setting, evapn. and condensation effects had negligible impact on the measured droplet size. The geometric mean diam. of droplets from coughing was 13.5 μm and it was 16.0 μm for speaking (counting 1-100). The estd. total no. of droplets expelled ranged from 947 to 2085 per cough and 112-6720 for speaking. The estd. droplet concns. for coughing ranged from 2.4 to 5.2 cm-3 per cough and 0.004-0.223 cm-3 for speaking.
- 26Xie, X.; Li, Y.; Chwang, A.; Ho, P.; Seto, W. How Far Droplets Can Move in Indoor Environments–Revisiting the Wells Evaporation-Falling Curve. Indoor Air 2007, 17 (3), 211– 225, DOI: 10.1111/j.1600-0668.2007.00469.x[Crossref], [PubMed], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2szjtFOrtw%253D%253D&md5=a751500d0142e767d36726d35204e03bHow far droplets can move in indoor environments--revisiting the Wells evaporation-falling curveXie X; Li Y; Chwang A T Y; Ho P L; Seto W HIndoor air (2007), 17 (3), 211-25 ISSN:0905-6947.UNLABELLED: A large number of infectious diseases are believed to be transmitted between people via large droplets and by airborne routes. An understanding of evaporation and dispersion of droplets and droplet nuclei is not only significant for developing effective engineering control methods for infectious diseases but also for exploring the basic transmission mechanisms of the infectious diseases. How far droplets can move is related to how far droplet-borne diseases can transmit. A simple physical model is developed and used here to investigate the evaporation and movement of droplets expelled during respiratory activities; in particular, the well-known Wells evaporation-falling curve of droplets is revisited considering the effect of relative humidity, air speed, and respiratory jets. Our simple model considers the movement of exhaled air, as well as the evaporation and movement of a single droplet. Exhaled air is treated as a steady-state non-isothermal (warm) jet horizontally issuing into stagnant surrounding air. A droplet is assumed to evaporate and move in this non-isothermal jet. Calculations are performed for both pure water droplets and droplets of sodium chloride (physiological saline) solution (0.9% w/v). We calculate the droplet lifetimes and how droplet size changes, as well as how far the droplets travel in different relative humidities. Our results indicate that a droplet's size predominately dictates its evaporation and movement after being expelled. The sizes of the largest droplets that would totally evaporate before falling 2 m away are determined under different conditions. The maximum horizontal distances that droplets can reach during different respiratory activities are also obtained. Our study is useful for developing effective prevention measures for controlling infectious diseases in hospitals and in the community at large. PRACTICAL IMPLICATIONS: Our study reveals that for respiratory exhalation flows, the sizes of the largest droplets that would totally evaporate before falling 2 m away are between 60 and 100 microm, and these expelled large droplets are carried more than 6 m away by exhaled air at a velocity of 50 m/s (sneezing), more than 2 m away at a velocity of 10 m/s (coughing) and less than 1 m away at a velocity of 1 m/s (breathing). These findings are useful for developing effective engineering control methods for infectious diseases, and also for exploring the basic transmission mechanisms of the infectious diseases. There is a need to examine the air distribution systems in hospital wards for controlling both airborne and droplet-borne transmitted diseases.
- 27Gralton, J.; Tovey, E.; McLaws, M.-L.; Rawlinson, W. D. The Role of Particle Size in Aerosolised Pathogen Transmission: A Review. J. Infect. 2011, 62 (1), 1– 13, DOI: 10.1016/j.jinf.2010.11.010[Crossref], [PubMed], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3M7islWksw%253D%253D&md5=eace75d8f8710c153e501d1fbea4f55fThe role of particle size in aerosolised pathogen transmission: a reviewGralton Jan; Tovey Euan; McLaws Mary-Louise; Rawlinson William DThe Journal of infection (2011), 62 (1), 1-13 ISSN:.Understanding respiratory pathogen transmission is essential for public health measures aimed at reducing pathogen spread. Particle generation and size are key determinant for pathogen carriage, aerosolisation, and transmission. Production of infectious respiratory particles is dependent on the type and frequency of respiratory activity, type and site of infection and pathogen load. Further, relative humidity, particle aggregation and mucus properties influence expelled particle size and subsequent transmission. Review of 26 studies reporting particle sizes generated from breathing, coughing, sneezing and talking showed healthy individuals generate particles between 0.01 and 500 μm, and individuals with infections produce particles between 0.05 and 500 μm. This indicates that expelled particles carrying pathogens do not exclusively disperse by airborne or droplet transmission but avail of both methods simultaneously and current dichotomous infection control precautions should be updated to include measures to contain both modes of aerosolised transmission.
- 28Kormuth, K. A.; Lin, K.; Prussin, A. J.; Vejerano, E. P.; Tiwari, A. J.; Cox, S. S.; Myerburg, M. M.; Lakdawala, S. S.; Marr, L. C. Influenza Virus Infectivity Is Retained in Aerosols and Droplets Independent of Relative Humidity. J. Infect. Dis. 2018, 218 (5), 739– 747, DOI: 10.1093/infdis/jiy221[Crossref], [PubMed], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlCntrfF&md5=2043db121617b8256bd6275904900984Influenza virus infectivity is retained in aerosols and droplets independent of relative humidityKormuth, Karen A.; Lin, Kaisen; Prussin, Aaron J., II; Vejerano, Eric P.; Tiwari, Andrea J.; Cox, Steve S.; Myerburg, Michael M.; Lakdawala, Seema S.; Marr, Linsey C.Journal of Infectious Diseases (2018), 218 (5), 739-747CODEN: JIDIAQ; ISSN:1537-6613. (Oxford University Press)Pandemic and seasonal influenza viruses can be transmitted through aerosols and droplets, in which viruses must remain stable and infectious across a wide range of environmental conditions. Using humidity-controlled chambers, we studied the impact of relative humidity on the stability of 2009 pandemic influenza A(H1N1) virus in suspended aerosols and stationary droplets. Contrary to the prevailing paradigm that humidity modulates the stability of respiratory viruses in aerosols, we found that viruses supplemented with material from the apical surface of differentiated primary human airway epithelial cells remained equally infectious for 1 h at all relative humidities tested. This sustained infectivity was obsd. in both fine aerosols and stationary droplets. Our data suggest, for the first time, that influenza viruses remain highly stable and infectious in aerosols across a wide range of relative humidities. These results have significant implications for understanding the mechanisms of transmission of influenza and its seasonality.
- 29Chen, C.; Zhao, B. Some questions on dispersion of human exhaled droplets in ventilation room: answers from numerical investigation. Indoor Air 2010, 20 (2), 95– 111, DOI: 10.1111/j.1600-0668.2009.00626.x[Crossref], [PubMed], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3c3nvVSlsQ%253D%253D&md5=649cbe46d55865ef0c4aa8cfdd151ab2Some questions on dispersion of human exhaled droplets in ventilation room: answers from numerical investigationChen C; Zhao BIndoor air (2010), 20 (2), 95-111 ISSN:.This study employs a numerical model to investigate the dispersion characteristics of human exhaled droplets in ventilation rooms. The numerical model is validated by two different experiments prior to the application for the studied cases. Some typical questions on studying dispersion of human exhaled droplets indoors are reviewed and numerical study using the normalized evaporation time and normalized gravitational sedimentation time was performed to obtain the answers. It was found that modeling the transient process from a droplet to a droplet nucleus due to evaporation can be neglected when the normalized evaporation time is <0.051. When the normalized gravitational sedimentation time is <0.005, the influence of ventilation rate could be neglected. However, the influence of ventilation pattern and initial exhaled velocity on the exhaled droplets dispersion is dominant as the airflow decides the droplets dispersion significantly. Besides, the influence of temperature and relative humidity on the dispersion of droplets can be neglected for the droplet with initial diameter <200 microm; while droplet nuclei size plays an important role only for the droplets with initial diameter within the range of 10 microm-100 microm. Practical Implications Dispersion of human exhaled droplets indoor is a key issue when evaluating human exposure to infectious droplets. Results from detailed numerical studies in this study reveal how the evaporation of droplets, ventilation rate, airflow pattern, initial exhaled velocity, and particle component decide the droplet dispersion indoor. The detailed analysis of these main influencing factors on droplet dispersion in ventilation rooms may help to guide (1) the selection of numerical approach, e.g., if the transient process from a droplet to a droplet nucleus due to evaporation should be incorporated to study droplet dispersion, and (2) the selection of ventilation system to minimize the spread of pathogen-laden droplets in an indoor environment.
- 30Mui, K. W.; Wong, L. T.; Wu, C. L.; Lai, A. C. Numerical modeling of exhaled droplet nuclei dispersion and mixing in indoor environments. J. Hazard. Mater. 2009, 167 (1–3), 736– 744, DOI: 10.1016/j.jhazmat.2009.01.041[Crossref], [PubMed], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmt1Giu7c%253D&md5=1bd81bc9fbcceb99b0513120bfb2e779Numerical modeling of exhaled droplet nuclei dispersion and mixing in indoor environmentsMui, K. W.; Wong, L. T.; Wu, C. L.; Lai, Alvin C. K.Journal of Hazardous Materials (2009), 167 (1-3), 736-744CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)The increasing incidence of indoor airborne infections has prompted attention upon the investigation of expiratory droplet dispersion and transport in built environments. In this study, a source (i.e. a patient who generates droplets) and a receiver (i.e. a susceptible object other than the source) are modeled in a mech. ventilated room. The receiver's exposure to the droplet nuclei is analyzed under two orientations relative to the source. Two droplet nuclei, 0.1 and 10 μm, with different emission velocities, are selected to represent large expiratory droplets which can still be inhaled into the human respiratory tracts. The droplet dispersion and mixing characteristics under well-mixed and displacement ventilation schemes are evaluated and compared numerically. Results show that the droplet dispersion and mixing under displacement ventilation is consistently poorer. Very low concn. regions are also obsd. in the displacement scheme. For both ventilation schemes, the intake dose will be reduced substantially if the droplets are emitted under the face-to-wall orientation rather than the face-to-face orientation. Implications of using engineering strategies for reducing exposure are briefly discussed.
- 31Ai, Z. T.; Melikov, A. K. Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review. Indoor Air 2018, 28 (4), 500– 524, DOI: 10.1111/ina.12465[Crossref], [PubMed], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MjlsVOqtQ%253D%253D&md5=1d3c98a32cd8da6fcac847964f281201Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A reviewAi Z T; Melikov A KIndoor air (2018), 28 (4), 500-524 ISSN:.This article reviews past studies of airborne transmission between occupants in indoor environments, focusing on the spread of expiratory droplet nuclei from mouth/nose to mouth/nose for non-specific diseases. Special attention is paid to summarizing what is known about the influential factors, the inappropriate simplifications of the thermofluid boundary conditions of thermal manikins, the challenges facing the available experimental techniques, and the limitations of available evaluation methods. Secondary issues are highlighted, and some new ways to improve our understanding of airborne transmission indoors are provided. The characteristics of airborne spread of expiratory droplet nuclei between occupants, which are influenced correlatively by both environmental and personal factors, were widely revealed under steady-state conditions. Owing to the different boundary conditions used, some inconsistent findings on specific influential factors have been published. The available instrumentation was too slow to provide accurate concentration profiles for time-dependent evaluations of events with obvious time characteristics, while computational fluid dynamics (CFD) studies were mainly performed in the framework of inherently steady Reynolds-averaged Navier-Stokes modeling. Future research needs in 3 areas are identified: the importance of the direction of indoor airflow patterns, the dynamics of airborne transmission, and the application of CFD simulations.
- 32Nicas, M.; Best, D. A Study Quantifying the Hand-to-Face Contact Rate and Its Potential Application to Predicting Respiratory Tract Infection. J. Occup. Environ. Hyg. 2008, 5 (6), 347– 352, DOI: 10.1080/15459620802003896[Crossref], [PubMed], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD1c7pvVerug%253D%253D&md5=e32c53a0e57143adad9efb2d449f5ed0A study quantifying the hand-to-face contact rate and its potential application to predicting respiratory tract infectionNicas Mark; Best DanielJournal of occupational and environmental hygiene (2008), 5 (6), 347-52 ISSN:.A substantial portion of human respiratory tract infection is thought to be transmitted via contaminated hand contact with the mouth, eyes, and/or nostrils. Thus, a key risk factor for infection transmission should be the rate of hand contact with these areas termed target facial membranes. A study was conducted in which 10 subjects were each videotaped for 3 hr while performing office-type work in isolation from other persons. The number of contacts to the eyes, nostrils, and lips was scored during subsequent viewing of the tapes. The total contacts per subject had sample mean x = 47 and sample standard deviation s = 34. The average total contact rate per hour was 15.7. The authors developed a relatively simple algebraic model for estimating the dose of pathogens transferred to target facial membranes during a defined exposure period. The model considers the rate of pathogen transfer to the hands via contact with contaminated environmental surfaces, and the rate of pathogen loss from the hands due to pathogen die-off and transfer from the hands to environmental surfaces and to target facial membranes during touching. The estimation of infection risk due to this dose also is discussed. A hypothetical but plausible example involving influenza A virus transmission is presented to illustrate the model.
- 33Nicas, M.; Sun, G. An Integrated Model of Infection Risk in a Health-Care Environment. Risk Anal 2006, 26 (4), 1085– 1096, DOI: 10.1111/j.1539-6924.2006.00802.x[Crossref], [PubMed], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD28rislaqsw%253D%253D&md5=0ab91b4ffc0c419d60891cea1d00bf38An integrated model of infection risk in a health-care environmentNicas Mark; Sun GangRisk analysis : an official publication of the Society for Risk Analysis (2006), 26 (4), 1085-96 ISSN:0272-4332.Certain respiratory tract infections can be transmitted by hand-to-mucous-membrane contact, inhalation, and/or direct respiratory droplet spray. In a room occupied by a patient with such a transmissible infection, pathogens present on textile and nontextile surfaces, and pathogens present in the air, provide sources of exposure for an attending health-care worker (HCW); in addition, close contact with the patient when the latter coughs allows for droplet spray exposure. We present an integrated model of pertinent source-environment-receptor pathways, and represent physical elements in these pathways as "states" in a discrete-time Markov chain model. We estimate the rates of transfer at various steps in the pathways, and their relationship to the probability that a pathogen in one state has moved to another state by the end of a specified time interval. Given initial pathogen loads on textile and nontextile surfaces and in room air, we use the model to estimate the expected pathogen dose to a HCW's mucous membranes and respiratory tract. In turn, using a nonthreshold infectious dose model, we relate the expected dose to infection risk. The system is illustrated with a hypothetical but plausible scenario involving a viral pathogen emitted via coughing. We also use the model to show that a biocidal finish on textile surfaces has the potential to substantially reduce infection risk via the hand-to-mucous-membrane exposure pathway.
- 34Tellier, R. Aerosol Transmission of Influenza A Virus: A Review of New Studies. J. R. Soc., Interface 2009, 6, S783– S790, DOI: 10.1098/rsif.2009.0302.focus
- 35Wells, W. On Air-Borne Infection: Study II. Droplets and Droplet Nuclei. Am. J. Epidemiol. 1934, 20 (3), 611– 618, DOI: 10.1093/oxfordjournals.aje.a118097
- 36Kukkonen, J.; Vesala, T.; Kulmala, M. The Interdependence of Evaporation and Settling for Airborne Freely Falling Droplets. J. Aerosol Sci. 1989, 20 (7), 749– 763, DOI: 10.1016/0021-8502(89)90087-6[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXmtFOiurY%253D&md5=72d34039a0bc8188d34ceca2d30ce645The interdependence of evaporation and settling for airborne freely falling dropletsKukkonen, J.; Vesala, T.; Kulmala, M.Journal of Aerosol Science (1989), 20 (7), 749-63CODEN: JALSB7; ISSN:0021-8502.The results are presented of theor. investigations concerning the quasistationary evapn. of freely falling droplets in the continuum regime. The math. model is based on the simultaneous numerical soln. of the equations governing mass and heat transfer from the droplet surfaces. The model includes a description of forced convective mass and heat transfer due to free fall. The investigation were focused on estg. the effect of the competing evapn. and settling processes on the deposition of a population of monodisperse droplets. The model was applied to predict the evolution of water and NH3 droplets in gas mixts. contg. air and the vapor of evapg. species.
- 37World Health Organization. Infection Prevention and Control of Epidemic-and Pandemic-Prone Acute Respiratory Infections in Health Care. https://www.who.int/csr/bioriskreduction/infection_control/publication/en/ (accessed 2020-05-05).Google ScholarThere is no corresponding record for this reference.
- 38Alsved, M.; Bourouiba, L.; Duchaine, C.; Löndahl, J.; Marr, L. C.; Parker, S. T.; Prussin, A. J.; Thomas, R. J. Natural Sources and Experimental Generation of Bioaerosols: Challenges and Perspectives. Aerosol Sci. Technol. 2020, 54 (5), 547– 571, DOI: 10.1080/02786826.2019.1682509[Crossref], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFamsLjE&md5=eefcc3a6edf17af5858082a473da133cNatural sources and experimental generation of bioaerosols: Challenges and perspectivesAlsved, Malin; Bourouiba, Lydia; Duchaine, Caroline; Loendahl, Jakob; Marr, Linsey C.; Parker, Simon T.; Prussin, Aaron J. II; Thomas, Richard J.Aerosol Science and Technology (2020), 54 (5), 547-571CODEN: ASTYDQ; ISSN:0278-6826. (Taylor & Francis, Inc.)A review. Exptl. aerosol generation methods aim to represent natural processes; however, the complexity is not always captured and unforeseen variability may be introduced into the data. The current practices for natural and exptl. aerosol generation techniques are reviewed here. Recommendations for best practice are presented, and include characterization of starting material and spray fluid, rational selection of appropriate aerosol generators, and phys. and biol. characterization of the output aerosol. Reporting of bioaerosol research should capture sufficient detail to aid data interpretation, reduce variation, and facilitate comparison between research labs. Finally, future directions and challenges in bioaerosol generation are discussed.
- 39Poulain, S.; Bourouiba, L. Disease Transmission via Drops and Bubbles. Phys. Today 2019, 72 (5), 70– 71, DOI: 10.1063/PT.3.4211
- 40Kwon, S.-B.; Park, J.; Jang, J.; Cho, Y.; Park, D.-S.; Kim, C.; Bae, G.-N.; Jang, A. Study on the Initial Velocity Distribution of Exhaled Air from Coughing and Speaking. Chemosphere 2012, 87 (11), 1260– 1264, DOI: 10.1016/j.chemosphere.2012.01.032[Crossref], [PubMed], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XisFKitr8%253D&md5=52ca235530f50921480dd7426f2cceb7Study on the initial velocity distribution of exhaled air from coughing and speakingKwon, Soon-Bark; Park, Jaehyung; Jang, Jaeyoun; Cho, Youngmin; Park, Duck-Shin; Kim, Changsoo; Bae, Gwi-Nam; Jang, AmChemosphere (2012), 87 (11), 1260-1264CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)Increasing concerns about the spread of airborne pathogens such as severe acute respiratory syndrome (SARS) and novel swine-origin influenza A (H1N1) have attracted public attention to bioaerosols and protection against them. The airborne pathogens are likely to be expelled from coughing or speaking, so the phys. data of the exhaled particles plays a key role in analyzing the pathway of airborne viruses. The objective of this study was to analyze the initial velocity and the angle of the exhaled airflow from coughing and speaking of 17 males and 9 females using Particle Image Velocimetry (PIV) and acrylic indoor chamber. The results showed that the av. initial coughing velocity was 15.3 m/s for the males and 10.6 m/s for the females, while the av. initial speaking velocity was 4.07 m/s and 2.31 m/s resp. The angle of the exhaled air from coughing was around 38° for the males and 32° for the females, while that of the exhaled air from speaking was around 49° and 78° resp. Also, the linear relation between the tested subject's height and their coughing and speaking velocity was shown in this study.
- 41Duguid, J. P. The Size and the Duration of Air-Carriage of Respiratory Droplets and Droplet-Nuclei. Epidemiol. Infect. 1946, 44 (6), 471– 479, DOI: 10.1017/S0022172400019288
- 42Höppe, P. Temperatures of Expired Air under Varying Climatic Conditions. Int. J. Biometeorol. 1981, 25 (2), 127– 132, DOI: 10.1007/BF02184460[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADyaL3M3jvVyjsA%253D%253D&md5=fb9629dca876a9dafbfdec9da9b48774Temperatures of expired air under varying climate conditionsHoppe PInternational journal of biometeorology (1981), 25 (2), 127-32 ISSN:0020-7128.There is no expanded citation for this reference.
- 43Baldwin, P. E.; Maynard, A. D. A Survey of Wind Speeds in Indoor Workplaces. Ann. Occup. Hyg. 1998, 42 (5), 303– 313, DOI: 10.1016/S0003-4878(98)00031-3[Crossref], [PubMed], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXmtVOqsbo%253D&md5=c7830bfc22fe5491cc905c25bb3fe3d2A survey of wind speeds in indoor workplacesBaldwin, Peter E. J.; Maynard, Andrew D.Annals of Occupational Hygiene (1998), 42 (5), 303-313CODEN: AOHYA3; ISSN:0003-4878. (Elsevier Science Ltd.)The applicability of the inhalable convention for sampling aerosols relies on its being a valid model for typical sampling environments. The current convention is based on measurements carried out in external wind speeds between 1 and 4 m·s-1. However these measurements show a degree of wind speed dependence, and it is uncertain at present how valid the convention is for describing human aspiration efficiency outside these wind speed limits. Following concerns that wind speeds in many indoor workplaces may be significantly below this range, measurements have been made in 55 work areas covering a wide range of workplaces. Measurements have concd. on "background" wind speeds where the influence of specific air movement sources is minimized. The pooled wind speed measurements show a highly skewed distribution with an arithmetic mean of approx. 0.3 m·s-1. Approx. 85% of all individual measurements were below this mean value. No obvious correlation was found between wind speed distribution parameters and industry type, room size or ventilation type. A limited no. of comparisons were made between static anemometers and devices mounted on workers. It was found that modal wind speeds experience by workers were typically 0.05 m·s-1 higher than those measured using a static anemometer. These measurements agreed well with previously published data for similar workplaces as well as houses.
- 44Hoyt, T.; Arens, E.; Zhang, H. Extending air temperature setpoints: Simulated energy savings and design considerations for new and retrofit buildings. Build. Environ. 2015, 88, 89– 96, DOI: 10.1016/j.buildenv.2014.09.010
- 45Vejerano, E. P.; Marr, L. C. Physico-Chemical Characteristics of Evaporating Respiratory Fluid Droplets. J. R. Soc., Interface 2018, 15 (139), 20170939, DOI: 10.1098/rsif.2017.0939[Crossref], [PubMed], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFyksrbJ&md5=de2a7595c5481ed9943716c8d53c475aPhysico-chemical characteristics of evaporating respiratory fluid dropletsVejerano, Eric P.; Marr, Linsey C.Journal of the Royal Society, Interface (2018), 15 (139), 20170939/1-20170939/10CODEN: JRSICU; ISSN:1742-5662. (Royal Society)The detailed physico-chem. characteristics of respiratory droplets in ambient air, where they are subject to evapn., are poorly understood. Changes in the concn. and phase of major components in a droplet-salt (NaCl), protein (mucin) and surfactant (dipalmitoylphosphatidylcholine)-may affect the viability of any pathogens contained within it and thus may affect the efficiency of transmission of infectious disease by droplets and aerosols. The objective of this study is to investigate the effect of relative humidity (RH) on the physico-chem. characteristics of evapg. droplets of model respiratory fluids. We labeled these components in model respiratory fluids and obsd. evapg. droplets suspended on a superhydrophobic surface using optical and fluorescence microscopy. When exposed to continuously decreasing RH, droplets of different model respiratory fluids assumed different morphologies. Loss of water induced phase sepn. as well as indication of a decrease in pH. The presence of surfactant inhibited the rapid rehydration of the non-volatile components. An enveloped virus, φ6, that has been proposed as a surrogate for influenza virus appeared to be homogeneously distributed throughout the dried droplet. We hypothesize that the increasing acidity and salinity in evapg. respiratory droplets may affect the structure of the virus, although at low enough RH, crystn. of the droplet components may eliminate their harmful effects.
- 46Bahl, P.; Doolan, C.; de Silva, C.; Chughtai, A. A.; Bourouiba, L.; MacIntyre, C. R. Airborne or Droplet Precautions for Health Workers Treating COVID-19?. J. Infect. Dis. 2020, DOI: 10.1093/infdis/jiaa189
- 47Shakya, K. M.; Noyes, A.; Kallin, R.; Peltier, R. E. Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure. J. Exposure Sci. Environ. Epidemiol. 2017, 27 (3), 352– 357, DOI: 10.1038/jes.2016.42[Crossref], [PubMed], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtl2mt7bO&md5=fc3dbb5a4b0b5b5e7985c9917e889140Evaluating the efficacy of cloth facemasks in reducing particulate matter exposureShakya, Kabindra M.; Noyes, Alyssa; Kallin, Randa; Peltier, Richard E.Journal of Exposure Science & Environmental Epidemiology (2017), 27 (3), 352-357CODEN: JESEBS; ISSN:1559-0631. (Nature Publishing Group)Inexpensive cloth masks are widely used in developing countries to protect from particulate pollution albeit limited data on their efficacy exists. This study examd. the efficiency of four types of masks (three types of cloth masks and one type of surgical mask) commonly worn in the developing world. Five monodispersed aerosol sphere size (30, 100, and 500 nm, and 1 and 2.5 μm) and dild. whole diesel exhaust was used to assess facemask performance. Among the three cloth mask types, a cloth mask with an exhaust valve performed best with filtration efficiency of 80-90% for the measured polystyrene latex (PSL) particle sizes. Two styles of com. available fabric masks were the least effective with a filtration efficiency of 39-65% for PSL particles, and they performed better as the particle size increased. When the cloth masks were tested against lab-generated whole diesel particles, the filtration efficiency for three particle sizes (30, 100, and 500 nm) ranged from 15% to 57%. Std. N95 mask performance was used as a control to compare the results with cloth masks, and our results suggest that cloth masks are only marginally beneficial in protecting individuals from particles <2.5 μm. Compared with cloth masks, disposable surgical masks are more effective in reducing particulate exposure.
- 48Wolfel, R.; Corman, V. M.; Guggemos, W.; Seilmaier, M.; Zange, S.; Muller, M. A.; Niemeyer, D.; Jones, T. C.; Vollmar, P.; Rothe, C. Virological assessment of hospitalized patients with COVID-2019. Nature 2020, 581, 465– 469, DOI: 10.1038/s41586-020-2196-x[Crossref], [PubMed], [CAS], Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383pvVSjtQ%253D%253D&md5=c07f8994b50fb04df3fa21473c1be494Virological assessment of hospitalized patients with COVID-2019Wolfel Roman; Zange Sabine; Vollmar Patrick; Ehmann Rosina; Zwirglmaier Katrin; Corman Victor M; Muller Marcel A; Niemeyer Daniela; Jones Terry C; Bleicker Tobias; Brunink Sebastian; Schneider Julia; Drosten Christian; Guggemos Wolfgang; Seilmaier Michael; Wendtner Clemens; Jones Terry C; Rothe Camilla; Hoelscher MichaelNature (2020), 581 (7809), 465-469 ISSN:.Coronavirus disease 2019 (COVID-19) is an acute infection of the respiratory tract that emerged in late 2019(1,2). Initial outbreaks in China involved 13.8% of cases with severe courses, and 6.1% of cases with critical courses(3). This severe presentation may result from the virus using a virus receptor that is expressed predominantly in the lung(2,4); the same receptor tropism is thought to have determined the pathogenicity-but also aided in the control-of severe acute respiratory syndrome (SARS) in 2003(5). However, there are reports of cases of COVID-19 in which the patient shows mild upper respiratory tract symptoms, which suggests the potential for pre- or oligosymptomatic transmission(6-8). There is an urgent need for information on virus replication, immunity and infectivity in specific sites of the body. Here we report a detailed virological analysis of nine cases of COVID-19 that provides proof of active virus replication in tissues of the upper respiratory tract. Pharyngeal virus shedding was very high during the first week of symptoms, with a peak at 7.11 × 10(8) RNA copies per throat swab on day 4. Infectious virus was readily isolated from samples derived from the throat or lung, but not from stool samples-in spite of high concentrations of virus RNA. Blood and urine samples never yielded virus. Active replication in the throat was confirmed by the presence of viral replicative RNA intermediates in the throat samples. We consistently detected sequence-distinct virus populations in throat and lung samples from one patient, proving independent replication. The shedding of viral RNA from sputum outlasted the end of symptoms. Seroconversion occurred after 7 days in 50% of patients (and by day 14 in all patients), but was not followed by a rapid decline in viral load. COVID-19 can present as a mild illness of the upper respiratory tract. The confirmation of active virus replication in the upper respiratory tract has implications for the containment of COVID-19.
- 49Bar-On, Y. M.; Flamholz, A.; Phillips, R.; Milo, R. Science Forum: SARS-CoV-2 (COVID-19) by the numbers. eLife 2020, 9, e57309 DOI: 10.7554/eLife.57309
- 50Xing, Y.-F.; Xu, Y.-H.; Shi, M.-H.; Lian, Y.-X. The Impact of PM2. 5 on the Human Respiratory System. J. Thorac. Dis. 2016, 8 (1), E69 DOI: 10.3978/j.issn.2072-1439.2016.01.19
- 51Asadi, S.; Wexler, A. S.; Cappa, C. D.; Barreda, S.; Bouvier, N. M.; Ristenpart, W. D. Aerosol emission and superemission during human speech increase with voice loudness. Sci. Rep. 2019, 9 (1), 1– 10, DOI: 10.1038/s41598-019-38808-z[Crossref], [PubMed], [CAS], Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitVKrsrvL&md5=d1e10ff6dc9dbd100c2212be66338c0aThermo-mechanical contact problems and elastic behaviour of single and double sides functionally graded brake disks with temperature-dependent material propertiesBayat, Mehdi; Alarifi, Ibrahim M.; Khalili, Ali Akbar; El-Bagory, Tarek M. A. A.; Nguyen, Hoang Minh; Asadi, AminScientific Reports (2019), 9 (1), 1-16CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)A thermo-elastic contact problem of functionally graded materials (FGMs) rotating brake disk with different pure brake pad areas under temp. dependent material properties is solved by Finite Element Method (FEM). The properties of brake disk change gradually from metal to ceramic by power-law distribution along the radial direction from the inner to the outer surface. Areas of the pure pad are changing while the vertical force is const. The ratio of brake pad thickness to FGMs brake disk thickness is assumed 0.66. Two sources of thermal loads are considered: (1) Heat generation between the pad and brake disk due to contact friction, and (2) External thermal load due to a const. temp. at inner and outer surfaces. Mech. responses of FGMs disk are compared with several pad contact areas. The results for temp.-dependent and temp.-independent material properties are investigated and presented. The results show that the abs. value of the shear stress in temp.-dependent material can be greater than that for temp.-independent material. The radial stress for some specific grading index (n = 1.5) is compressive near the inner surface for double contact while it is tensile for a single contact. It is concluded that the radial strain for some specific value of grading index (n = 1) is lower than other FGMs and pure double side contact brake disks.
- 52Cedeño-Laurent, J. G.; Williams, A.; MacNaughton, P.; Cao, X.; Eitland, E.; Spengler, J.; Allen, J. Building Evidence for Health: Green Buildings, Current Science, and Future Challenges. Annu. Rev. Public Health 2018, 39 (1), 291– 308, DOI: 10.1146/annurev-publhealth-031816-044420[Crossref], [PubMed], [CAS], Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1Mvgt1ajug%253D%253D&md5=f9f4460df6f0e48e922131cf25c5db72Building Evidence for Health: Green Buildings, Current Science, and Future ChallengesCedeno-Laurent J G; Williams A; MacNaughton P; Cao X; Eitland E; Spengler J; Allen JAnnual review of public health (2018), 39 (), 291-308 ISSN:.Civilizational challenges have questioned the status quo of energy and material consumption by humans. From the built environment perspective, a response to these challenges was the creation of green buildings. Although the revolutionary capacity of the green building movement has elevated the expectations of new commercial construction, its rate of implementation has secluded the majority of the population from its benefits. Beyond reductions in energy usage and increases in market value, the main strength of green buildings may be the procurement of healthier building environments. Further pursuing the right to healthy indoor environments could help the green building movement to attain its full potential as a transformational public health tool. On the basis of 40 years of research on indoor environmental quality, we present a summary of nine environment elements that are foundational to human health. We posit the role of green buildings as a critical research platform within a novel sustainability framework based on social-environmental capital assets.
- 53Li, Y.; Leung, G. M.; Tang, J. W.; Yang, X.; Chao, C. Y.; Lin, J. Z.; Lu, J. W.; Nielsen, P. V.; Niu, J.; Qian, H. Role of Ventilation in Airborne Transmission of Infectious Agents in the Built Environment-a Multidisciplinary Systematic Review. Indoor Air 2007, 17 (1), 2– 18, DOI: 10.1111/j.1600-0668.2006.00445.x[Crossref], [PubMed], [CAS], Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2s%252FlsVajtw%253D%253D&md5=5b3cf1b64261320f3f32226ba12a161bRole of ventilation in airborne transmission of infectious agents in the built environment - a multidisciplinary systematic reviewLi Y; Leung G M; Tang J W; Yang X; Chao C Y H; Lin J Z; Lu J W; Nielsen P V; Niu J; Qian H; Sleigh A C; Su H-J J; Sundell J; Wong T W; Yuen P LIndoor air (2007), 17 (1), 2-18 ISSN:0905-6947.There have been few recent studies demonstrating a definitive association between the transmission of airborne infections and the ventilation of buildings. The severe acute respiratory syndrome (SARS) epidemic in 2003 and current concerns about the risk of an avian influenza (H5N1) pandemic, have made a review of this area timely. We searched the major literature databases between 1960 and 2005, and then screened titles and abstracts, and finally selected 40 original studies based on a set of criteria. We established a review panel comprising medical and engineering experts in the fields of microbiology, medicine, epidemiology, indoor air quality, building ventilation, etc. Most panel members had experience with research into the 2003 SARS epidemic. The panel systematically assessed 40 original studies through both individual assessment and a 2-day face-to-face consensus meeting. Ten of 40 studies reviewed were considered to be conclusive with regard to the association between building ventilation and the transmission of airborne infection. There is strong and sufficient evidence to demonstrate the association between ventilation, air movements in buildings and the transmission/spread of infectious diseases such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS. There is insufficient data to specify and quantify the minimum ventilation requirements in hospitals, schools, offices, homes and isolation rooms in relation to spread of infectious diseases via the airborne route. PRACTICAL IMPLICATION: The strong and sufficient evidence of the association between ventilation, the control of airflow direction in buildings, and the transmission and spread of infectious diseases supports the use of negatively pressurized isolation rooms for patients with these diseases in hospitals, in addition to the use of other engineering control methods. However, the lack of sufficient data on the specification and quantification of the minimum ventilation requirements in hospitals, schools and offices in relation to the spread of airborne infectious diseases, suggest the existence of a knowledge gap. Our study reveals a strong need for a multidisciplinary study in investigating disease outbreaks, and the impact of indoor air environments on the spread of airborne infectious diseases.
- 54Ai, Z. T.; Huang, T.; Melikov, A. K. Airborne Transmission of Exhaled Droplet Nuclei between Occupants in a Room with Horizontal Air Distribution. Build. Environ. 2019, 163, 106328, DOI: 10.1016/j.buildenv.2019.106328
- 55Li, Y.; Nielsen, P. V. CFD and ventilation research. Indoor Air 2011, 21 (6), 442– 453, DOI: 10.1111/j.1600-0668.2011.00723.x[Crossref], [PubMed], [CAS], Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3MbjsFWktQ%253D%253D&md5=f240d6e1a739c5c0b882e27f2997b915CFD and ventilation researchLi Y; Nielsen P VIndoor air (2011), 21 (6), 442-53 ISSN:.UNLABELLED: There has been a rapid growth of scientific literature on the application of computational fluid dynamics (CFD) in the research of ventilation and indoor air science. With a 1000-10,000 times increase in computer hardware capability in the past 20 years, CFD has become an integral part of scientific research and engineering development of complex air distribution and ventilation systems in buildings. This review discusses the major and specific challenges of CFD in terms of turbulence modelling, numerical approximation, and boundary conditions relevant to building ventilation. We emphasize the growing need for CFD verification and validation, suggest ongoing needs for analytical and experimental methods to support the numerical solutions, and discuss the growing capacity of CFD in opening up new research areas. We suggest that CFD has not become a replacement for experiment and theoretical analysis in ventilation research, rather it has become an increasingly important partner. PRACTICAL IMPLICATIONS: We believe that an effective scientific approach for ventilation studies is still to combine experiments, theory, and CFD. We argue that CFD verification and validation are becoming more crucial than ever as more complex ventilation problems are solved. It is anticipated that ventilation problems at the city scale will be tackled by CFD in the next 10 years.
- 56Ramponi, R.; Blocken, B. CFD simulation of cross-ventilation for a generic isolated building: impact of computational parameters. Build. Sci. 2012, 53, 34– 48, DOI: 10.1016/j.buildenv.2012.01.004
- 57Owen, M. S. ASHRAE Handbook: HVAC Systems and Equipment; American Society of Heating, Refrigerating and Air-Conditioning Engineers: Atlanta, 2004.Google ScholarThere is no corresponding record for this reference.
- 58Weather Averages for the United States.https://www.currentresults.com/Weather/US/weather-averages-index.php (accessed 2020-05-07).Google ScholarThere is no corresponding record for this reference.
- 59Liao, L.; Xiao, W.; Zhao, M.; Yu, X.; Wang, H.; Wang, Q.; Chu, S.; Cui, Y. Can N95 Respirators Be Reused after Disinfection? How Many Times?. ACS Nano 2020, 14 (5), 6348– 6356, DOI: 10.1021/acsnano.0c03597[ACS Full Text
], [CAS], Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXosVCmt7o%253D&md5=5fc1b3a9b67826faa66784801f5cf1d8Can N95 Respirators Be Reused after Disinfection? How Many Times?Liao, Lei; Xiao, Wang; Zhao, Mervin; Yu, Xuanze; Wang, Haotian; Wang, Qiqi; Chu, Steven; Cui, YiACS Nano (2020), 14 (5), 6348-6356CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The coronavirus disease 2019 (COVID-19) pandemic has led to a major shortage of N95 respirators, which are essential for protecting healthcare professionals and the general public who may come into contact with the virus. Thus, it is essential to det. how we can reuse respirators and other personal protective equipment in these urgent times. We investigated multiple commonly used disinfection schemes on media with particle filtration efficiency of 95%. Heating was recently found to inactivate the virus in soln. within 5 min at 70°C and is among the most scalable, user-friendly methods for viral disinfection. We found that heat (≤85°C) under various humidities (≤100% relative humidity, RH) was the most promising, nondestructive method for the preservation of filtration properties in meltblown fabrics as well as N95-grade respirators. At 85°C, 30% RH, we were able to perform 50 cycles of heat treatment without significant changes in the filtration efficiency. At low humidity or dry conditions, temps. up to 100°C were not found to alter the filtration efficiency significantly within 20 cycles of treatment. UV irradn. was a secondary choice, which was able to withstand 10 cycles of treatment and showed small degrdn. by 20 cycles. However, UV can potentially impact the material strength and subsequent sealing of respirators. Finally, treatments involving liqs. and vapors require caution, as steam, alc., and household bleach all may lead to degrdn. of the filtration efficiency, leaving the user vulnerable to the viral aerosols. - 60Zhao, M.; Liao, L.; Xiao, W.; Yu, X.; Wang, H.; Wang, Q.; Lin, Y. L.; Kilinc-Balci, F. S.; Price, A.; Chu, L.; Chu, M. C.; Chu, S.; Cui, Y. Household materials selection for homemade cloth face coverings and their filtration efficiency enhancement with triboelectric charging. Nano Lett. 2020, 20 (7), 5544– 5552, DOI: 10.1021/acs.nanolett.0c02211[ACS Full Text], [CAS], Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVOmtLbJ&md5=27921343d002cc18bed5f34b01f0c29fHousehold Materials Selection for Homemade Cloth Face Coverings and Their Filtration Efficiency Enhancement with Triboelectric ChargingZhao, Mervin; Liao, Lei; Xiao, Wang; Yu, Xuanze; Wang, Haotian; Wang, Qiqi; Lin, Ying Ling; Kilinc-Balci, F. Selcen; Price, Amy; Chu, Larry; Chu, May C.; Chu, Steven; Cui, YiNano Letters (2020), 20 (7), 5544-5552CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The COVID-19 pandemic is currently causing a severe disruption and shortage in the global supply chain of necessary personal protective equipment (e.g., N95 respirators). The U.S. CDC has recommended use of household cloth by the general public to make cloth face coverings as a method of source control. We evaluated the filtration properties of natural and synthetic materials using a modified procedure for N95 respirator approval. Common fabrics of cotton, polyester, nylon, and silk had filtration efficiency of 5-25%, polypropylene spunbond had filtration efficiency 6-10%, and paper-based products had filtration efficiency of 10-20%. An advantage of polypropylene spunbond is that it can be simply triboelec. charged to enhance the filtration efficiency (from 6 to >10%) without any increase in pressure (stable overnight and in humid environments). Using the filtration quality factor, fabric microstructure, and charging ability, we are able to provide an assessment of suggested fabric materials for homemade facial coverings.
- 61Konda, A.; Prakash, A.; Moss, G. A.; Schmoldt, M.; Grant, G. D.; Guha, S. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS Nano 2020, 14 (5), 6339– 6347, DOI: 10.1021/acsnano.0c03252[ACS Full Text], [CAS], Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnslChsr4%253D&md5=961b798525395cbb0bc53e325418e39dAerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth MasksKonda, Abhiteja; Prakash, Abhinav; Moss, Gregory A.; Schmoldt, Michael; Grant, Gregory D.; Guha, SupratikACS Nano (2020), 14 (5), 6339-6347CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, resp., the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton-silk, cotton-chiffon, cotton-flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mech. and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (i.e., thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of "fit" and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.
Cited By
This article is cited by 8 publications.
- Longyi Shao, Shuoyi Ge, Tim Jones, M. Santosh, Luis F.O. Silva, Yaxin Cao, Marcos L.S. Oliveira, Mengyuan Zhang, Kelly BéruBé. The role of airborne particles and environmental considerations in the transmission of SARS-CoV-2. Geoscience Frontiers 2021, 12 (5) , 101189. https://doi.org/10.1016/j.gsf.2021.101189
- Luise N. Nottmeyer, Francesco Sera. Influence of temperature, and of relative and absolute humidity on COVID-19 incidence in England - A multi-city time-series study. Environmental Research 2021, 196 , 110977. https://doi.org/10.1016/j.envres.2021.110977
- Al-Ekram Elahee Hridoy, Md. Abdul Mohiman, Shekh Md. Shajid Hasan Tusher, Sayed Ziaul Amin Nowraj, Mohammad Atiqur Rahman. Impact of meteorological parameters on COVID-19 transmission in Bangladesh: a spatiotemporal approach. Theoretical and Applied Climatology 2021, 144 (1-2) , 273-285. https://doi.org/10.1007/s00704-021-03535-x
- Tahl Zimmerman, Shahida Anusha Siddiqui, Werner Bischoff, Salam A. Ibrahim. Tackling Airborne Virus Threats in the Food Industry: A Proactive Approach. International Journal of Environmental Research and Public Health 2021, 18 (8) , 4335. https://doi.org/10.3390/ijerph18084335
- Jialei Shen, Meng Kong, Bing Dong, Michael J. Birnkrant, Jianshun Zhang. A systematic approach to estimating the effectiveness of multi-scale IAQ strategies for reducing the risk of airborne infection of SARS-CoV-2. Building and Environment 2021, vols. 1–3 , 107926. https://doi.org/10.1016/j.buildenv.2021.107926
- Daniel M. Campagne. The problem with communication stress from face masks. Journal of Affective Disorders Reports 2021, 3 , 100069. https://doi.org/10.1016/j.jadr.2020.100069
- X. Sophie Zhang, Caroline Duchaine. SARS-CoV-2 and Health Care Worker Protection in Low-Risk Settings: a Review of Modes of Transmission and a Novel Airborne Model Involving Inhalable Particles. Clinical Microbiology Reviews 2020, 34 (1) https://doi.org/10.1128/CMR.00184-20
- Purnamita Dasgupta, Kavitha Srikanth. Reduced air pollution during COVID-19: Learnings for sustainability from Indian Cities. Global Transitions 2020, 2 , 271-282. https://doi.org/10.1016/j.glt.2020.10.002
Abstract
Figure 1
Figure 1. Transmission of COVID-19 through droplets and aerosol particles. After being exhaled by a patient, respiratory droplets with various sizes will travel and simultaneously evaporate in the ambient environment. Small-sized droplets dry immediately to form a cloud of aerosol particles. These particles will suspend in the air for a significant amount of time. Large-sized droplets can reach a limited distance and fall to the ground due to gravity. We define Lmax as the maximum horizontal distance that droplets can travel before they either become dry aerosol particles or descend below the level of another person’s hands, i.e., H/2 from the ground, where H is the height of another person.
Figure 2
Figure 2. Effect of environmental factors on the transmission of COVID-19 via means of droplet contact and exposure to aerosol particles, respectively. (a) Maximum droplet traveling distance Lmax under different weather conditions in terms of temperature and relative humidity. Droplets can reach a longer distance in a cool and humid environment. (b) Aerosolization rate φa, defined as the percentage of respiratory droplets turning into aerosol particles that can potentially travel beyond Lmax, under different weather conditions in terms of temperature and humidity. (c) Average diameter of completely dry aerosol particles, under different weather conditions. (d) Total mass of PM2.5 floating in air that are produced by respiratory droplets per person at steady state in an enclosed space.
Figure 3
Figure 3. Effect of a horizontal, constant background airflow. Droplet spreading distance Lmax as a function of a horizontal, constant air speed.
Figure 4
Figure 4. Geographical distribution of droplet spreading distance and aerosolization rate across the United States. (a) Spreading distance Lmax and (b) aerosolization rate φa in each U.S. state based on its monthly average weather condition in August. County-by-county distribution of (c) spreading distance Lmax and (d) aerosolization rate φa in California based on their monthly average weather conditions for August afternoons. (e) Safe distance Lmax and (f) aerosolization rate φa in major U.S. cities in summer and winter. Indoor wind speed is assumed (Vair = 0.3 m/s).
References
ARTICLE SECTIONSThis article references 61 other publications.
- 1Dong, E.; Du, H.; Gardner, L. An Interactive Web-Based Dashboard to Track COVID-19 in Real Time. Lancet Infect. Dis. 2020, 20 (5), 533– 534, DOI: 10.1016/S1473-3099(20)30120-1[Crossref], [PubMed], [CAS], Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksVaisbs%253D&md5=7f528642a4d2b2fcc3575e37085819a8An interactive web-based dashboard to track COVID-19 in real timeDong, Ensheng; Du, Hongru; Gardner, LaurenLancet Infectious Diseases (2020), 20 (5), 533-534CODEN: LIDABP; ISSN:1473-3099. (Elsevier Ltd.)The authors describe the development of an online interactive dashboard, hosted by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University, Baltimore, MD, USA, to visualize and track reported cases of coronavirus disease 2019 (COVID-19) in real time. The dashboard, first shared publicly on Jan 22, illustrates the location and no. of confirmed COVID-19 cases, deaths, and recoveries for all affected countries. It was developed to provide researchers, public health authorities, and the general public with a user-friendly tool to track the outbreak as it unfolds. All data collected and displayed are made freely available, initially through Google Sheets and now through a GitHub repository, along with the feature layers of the dashboard, which are now included in the Esri Living Atlas.
- 2Zhou, P.; Yang, X.-L.; Wang, X.-G.; Hu, B.; Zhang, L.; Zhang, W.; Si, H.-R.; Zhu, Y.; Li, B.; Huang, C.-L.; others A Pneumonia Outbreak Associated with a New Coronavirus of Probable Bat Origin. Nature 2020, 579 (7798), 270– 273, DOI: 10.1038/s41586-020-2012-7[Crossref], [PubMed], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksFKlsLg%253D&md5=236f17d4d3c7978d72513e5e0258f1b3A pneumonia outbreak associated with a new coronavirus of probable bat originZhou, Peng; Yang, Xing-Lou; Wang, Xian-Guang; Hu, Ben; Zhang, Lei; Zhang, Wei; Si, Hao-Rui; Zhu, Yan; Li, Bei; Huang, Chao-Lin; Chen, Hui-Dong; Chen, Jing; Luo, Yun; Guo, Hua; Jiang, Ren-Di; Liu, Mei-Qin; Chen, Ying; Shen, Xu-Rui; Wang, Xi; Zheng, Xiao-Shuang; Zhao, Kai; Chen, Quan-Jiao; Deng, Fei; Liu, Lin-Lin; Yan, Bing; Zhan, Fa-Xian; Wang, Yan-Yi; Xiao, Geng-Fu; Shi, Zheng-LiNature (London, United Kingdom) (2020), 579 (7798), 270-273CODEN: NATUAS; ISSN:0028-0836. (Nature Research)Abstr.: Since the outbreak of severe acute respiratory syndrome (SARS) 18 years ago, a large no. of SARS-related coronaviruses (SARSr-CoVs) have been discovered in their natural reservoir host, bats1-4. Previous studies have shown that some bat SARSr-CoVs have the potential to infect humans5-7. Here we report the identification and characterization of a new coronavirus (2019-nCoV), which caused an epidemic of acute respiratory syndrome in humans in Wuhan, China. The epidemic, which started on 12 Dec. 2019, had caused 2,794 lab.-confirmed infections including 80 deaths by 26 Jan. 2020. Full-length genome sequences were obtained from five patients at an early stage of the outbreak. The sequences are almost identical and share 79.6% sequence identity to SARS-CoV. Furthermore, we show that 2019-nCoV is 96% identical at the whole-genome level to a bat coronavirus. Pairwise protein sequence anal. of seven conserved non-structural proteins domains show that this virus belongs to the species of SARSr-CoV. In addn., 2019-nCoV virus isolated from the bronchoalveolar lavage fluid of a critically ill patient could be neutralized by sera from several patients. Notably, we confirmed that 2019-nCoV uses the same cell entry receptor-angiotensin converting enzyme II (ACE2)-as SARS-CoV.
- 3Wu, F.; Zhao, S.; Yu, B.; Chen, Y.-M.; Wang, W.; Song, Z.-G.; Hu, Y.; Tao, Z.-W.; Tian, J.-H.; Pei, Y.-Y.; others A New Coronavirus Associated with Human Respiratory Disease in China. Nature 2020, 579 (7798), 265– 269, DOI: 10.1038/s41586-020-2008-3[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXksFKlsLc%253D&md5=0163a684829e880a0c3347e19f0ce52aA new coronavirus associated with human respiratory disease in ChinaWu, Fan; Zhao, Su; Yu, Bin; Chen, Yan-Mei; Wang, Wen; Song, Zhi-Gang; Hu, Yi; Tao, Zhao-Wu; Tian, Jun-Hua; Pei, Yuan-Yuan; Yuan, Ming-Li; Zhang, Yu-Ling; Dai, Fa-Hui; Liu, Yi; Wang, Qi-Min; Zheng, Jiao-Jiao; Xu, Lin; Holmes, Edward C.; Zhang, Yong-ZhenNature (London, United Kingdom) (2020), 579 (7798), 265-269CODEN: NATUAS; ISSN:0028-0836. (Nature Research)Emerging infectious diseases, such as severe acute respiratory syndrome (SARS) and Zika virus disease, present a major threat to public health. Despite intense research efforts, how, when and where new diseases appear are still a source of considerable uncertainty. A severe respiratory disease was recently reported in Wuhan, Hubei province, China. As of 25 Jan. 2020, at least 1,975 cases had been reported since the first patient was hospitalized on 12 Dec. 2019. Epidemiol. investigations have suggested that the outbreak was assocd. with a seafood market in Wuhan. Here we study a single patient who was a worker at the market and who was admitted to the Central Hospital of Wuhan on 26 Dec. 2019 while experiencing a severe respiratory syndrome that included fever, dizziness and a cough. Metagenomic RNA sequencing of a sample of bronchoalveolar lavage fluid from the patient identified a new RNA virus strain from the family Coronaviridae, which is designated here 'WH-Human 1' coronavirus (and has also been referred to as '2019-nCoV'). Phylogenetic anal. of the complete viral genome (29,903 nucleotides) revealed that the virus was most closely related (89.1% nucleotide similarity) to a group of SARS-like coronaviruses (genus Betacoronavirus, subgenus Sarbecovirus) that had previously been found in bats in China. This outbreak highlights the ongoing ability of viral spill-over from animals to cause severe disease in humans.
- 4Guan, W.; Ni, Z.; Hu, Y.; Liang, W.; Ou, C.; He, J.; Liu, L.; Shan, H.; Lei, C.; Hui, D. S.; others Clinical Characteristics of Coronavirus Disease 2019 in China. N. Engl. J. Med. 2020, 382 (18), 1708– 1720, DOI: 10.1056/NEJMoa2002032[Crossref], [PubMed], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXovVSjsb8%253D&md5=db6fa99e647c6ba6862ad1d795118ab1Clinical characteristics of coronavirus disease 2019 in ChinaGuan, W.; Ni, Z.; Hu, Yu; Liang, W.; Ou, C.; He, J.; Liu, L.; Shan, H.; Lei, C.; Hui, D. S. C.; Du, B.; Li, L.; Zeng, G.; Yuen, K.-Y.; Chen, R.; Tang, C.; Wang, T.; Chen, P.; Xiang, J.; Li, S.; Wang, Jin-lin; Liang, Z.; Peng, Y.; Wei, L.; Liu, Y.; Hu, Ya-hua; Peng, P.; Wang, Jian-ming; Liu, J.; Chen, Z.; Li, G.; Zheng, Z.; Qiu, S.; Luo, J.; Ye, C.; Zhu, S.; Zhong, N.New England Journal of Medicine (2020), 382 (18), 1708-1720CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)Background: Since Dec. 2019, when coronavirus disease 2019 (Covid-19) emerged in Wuhan city and rapidly spread throughout China, data have been needed on the clin. characteristics of the affected patients. Methods: We extd. data regarding 1099 patients with lab.-confirmed Covid-19 from 552 hospitals in 30 provinces, autonomous regions, and municipalities in mainland China through Jan. 29, 2020. The primary composite end point was admission to an intensive care unit (ICU), the use of mech. ventilation, or death. results The median age of the patients was 47 years; 41.9% of the patients were female. The primary composite end point occurred in 67 patients (6.1%), including 5.0% who were admitted to the ICU, 2.3% who underwent invasive mech. ventilation, and 1.4% who died. Only 1.9% of the patients had a history of direct contact with wildlife. Among nonresidents of Wuhan, 72.3% had contact with residents of Wuhan, including 31.3% who had visited the city. The most common symptoms were fever (43.8% on admission and 88.7% during hospitalization) and cough (67.8%). Diarrhea was uncommon (3.8%). The median incubation period was 4 days (interquartile range, 2 to 7). On admission, ground-glass opacity was the most common radiol. finding on chest computed tomog. (CT) (56.4%). No radiog. or CT abnormality was found in 157 of 877 patients (17.9%) with nonsevere disease and in 5 of 173 patients (2.9%) with severe disease. Lymphocytopenia was present in 83.2% of the patients on admission.hCt scan. Conclusions: During the first 2 mo of the current outbreak, Covid-19 spread rapidly throughout China and caused varying degrees of illness. Patients often presented without fever, and many did not have abnormal radiol. findings.
- 5Letko, M.; Marzi, A.; Munster, V. Functional Assessment of Cell Entry and Receptor Usage for SARS-CoV-2 and Other Lineage B Betacoronaviruses. Nat. Microbiol. 2020, 5 (4), 562– 569, DOI: 10.1038/s41564-020-0688-y[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXjvFyitL0%253D&md5=98931812734d0f364d4d0c5f88a9d165Functional assessment of cell entry and receptor usage for SARS-CoV-2 and other lineage B betacoronavirusesLetko, Michael; Marzi, Andrea; Munster, VincentNature Microbiology (2020), 5 (4), 562-569CODEN: NMAICH; ISSN:2058-5276. (Nature Research)Over the past 20 years, several coronaviruses have crossed the species barrier into humans, causing outbreaks of severe, and often fatal, respiratory illness. Since SARS-CoV was first identified in animal markets, global viromics projects have discovered thousands of coronavirus sequences in diverse animals and geog. regions. Unfortunately, there are few tools available to functionally test these viruses for their ability to infect humans, which has severely hampered efforts to predict the next zoonotic viral outbreak. Here, we developed an approach to rapidly screen lineage B betacoronaviruses, such as SARS-CoV and the recent SARS-CoV-2, for receptor usage and their ability to infect cell types from different species. We show that host protease processing during viral entry is a significant barrier for several lineage B viruses and that bypassing this barrier allows several lineage B viruses to enter human cells through an unknown receptor. We also demonstrate how different lineage B viruses can recombine to gain entry into human cells, and confirm that human ACE2 is the receptor for the recently emerging SARS-CoV-2.
- 6Leung, K.; Wu, J. T.; Liu, D.; Leung, G. M. First-Wave COVID-19 Transmissibility and Severity in China Outside Hubei after Control Measures, and Second-Wave Scenario Planning: A Modelling Impact Assessment. Lancet 2020, 395 (10233), 1382– 1393, DOI: 10.1016/S0140-6736(20)30746-7[Crossref], [PubMed], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXntFSmurg%253D&md5=424307813486dc45252b6f235fd9de52First-wave COVID-19 transmissibility and severity in China outside Hubei after control measures, and second-wave scenario planning: a modelling impact assessmentLeung, Kathy; Wu, Joseph T.; Liu, Di; Leung, Gabriel M.Lancet (2020), 395 (10233), 1382-1393CODEN: LANCAO; ISSN:0140-6736. (Elsevier Ltd.)As of March 18, 2020, 13 415 confirmed cases and 120 deaths related to coronavirus disease 2019 (COVID-19) in mainland China, outside Hubei province-the epicentre of the outbreak-had been reported. Since late Jan., massive public health interventions have been implemented nationwide to contain the outbreak. We provide an impact assessment of the transmissibility and severity of COVID-19 during the first wave in mainland Chinese locations outside Hubei. We estd. the instantaneous reprodn. no. (Rt) of COVID-19 in Beijing, Shanghai, Shenzhen, Wenzhou, and the ten Chinese provinces that had the highest no. of confirmed COVID-19 cases; and the confirmed case-fatality risk (cCFR) in Beijing, Shanghai, Shenzhen, and Wenzhou, and all 31 Chinese provinces. We used a susceptible-infectious-recovered model to show the potential effects of relaxing containment measures after the first wave of infection, in anticipation of a possible second wave. In all selected cities and provinces, the Rt decreased substantially since Jan 23, when control measures were implemented, and have since remained below 1. The cCFR outside Hubei was 0·98% (95% CI 0·82-1·16), which was almost five times lower than that in Hubei (5·91%, 5·73-6·09). Relaxing the interventions (resulting in Rt >1) when the epidemic size was still small would increase the cumulative case count exponentially as a function of relaxation duration, even if aggressive interventions could subsequently push disease prevalence back to the baseline level. The first wave of COVID-19 outside of Hubei has abated because of aggressive non-pharmaceutical interventions. However, given the substantial risk of viral reintroduction, particularly from overseas importation, close monitoring of Rt and cCFR is needed to inform strategies against a potential second wave to achieve an optimal balance between health and economic protection. Health and Medical Research Fund, Hong Kong, China.
- 7Arons, M. M.; Hatfield, K. M.; Reddy, S. C. Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility. N. Engl. J. Med. 2020, 382, 2081– 2090, DOI: 10.1056/NEJMoa2008457[Crossref], [PubMed], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVGqsrfE&md5=2b91e64e3768320452df1608735568b5Presymptomatic SARS-CoV-2 infections and transmission in a skilled nursing facilityArons, M. M.; Hatfield, K. M.; Reddy, S. C.; Kimball, A.; James, A.; Jacobs, J. R.; Taylor, J.; Spicer, K.; Bardossy, A. C.; Oakley, L. P.; Tanwar, S.; Dyal, J. W.; Harney, J.; Chisty, Z.; Bell, J. M.; Methner, M.; Paul, P.; Carlson, C. M.; McLaughlin, H. P.; Thornburg, N.; Tong, S.; Tamin, A.; Tao, Y.; Uehara, A.; Harcourt, J.; Clark, S.; Brostrom-Smith, C.; Page, L. C.; Kay, M.; Lewis, J.; Montgomery, P.; Stone, N. D.; Clark, T. A.; Honein, M. A.; Duchin, J. S.; Jernigan, J. A.New England Journal of Medicine (2020), 382 (22), 2081-2090CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can spread rapidly within skilled nursing facilities. After identification of a case of Covid-19 in a skilled nursing facility, we assessed transmission and evaluated the adequacy of symptom-based screening to identify infections in residents. Methods: We conducted two serial point-prevalence surveys, 1 wk apart, in which assenting residents of the facility underwent nasopharyngeal and oropharyngeal testing for SARS-CoV-2, including real-time reverse-transcriptase polymerase chain reaction (rRT-PCR), viral culture, and sequencing. Symptoms that had been present during the preceding 14 days were recorded. Asymptomatic residents who tested pos. were reassessed 7 days later. Residents with SARS-CoV-2 infection were categorized as symptomatic with typical symptoms (fever, cough, or shortness of breath), symptomatic with only atypical symptoms, presymptomatic, or asymptomatic. Results: Twenty-three days after the first pos. test result in a resident at this skilled nursing facility, 57 of 89 residents (64%) tested pos. for SARS-CoV-2. Among 76 residents who participated in point-prevalence surveys, 48 (63%) tested pos. Of these 48 residents, 27 (56%) were asymptomatic at the time of testing; 24 subsequently developed symptoms (median time to onset, 4 days). Samples from these 24 presymptomatic residents had a median rRT-PCR cycle threshold value of 23.1, and viable virus was recovered from 17 residents. As of Apr. 3, of the 57 residents with SARS-CoV-2 infection, 11 had been hospitalized (3 in the intensive care unit) and 15 had died (mortality, 26%). Of the 34 residents whose specimens were sequenced, 27 (79%) had sequences that fit into two clusters with a difference of one nucleotide. Conclusions: Rapid and widespread transmission of SARS-CoV-2 was demonstrated in this skilled nursing facility. More than half of residents with pos. test results were asymptomatic at the time of testing and most likely contributed to transmission. Infection-control strategies focused solely on symptomatic residents were not sufficient to prevent transmission after SARS-CoV-2 introduction into this facility.
- 8Booth, T. F.; Kournikakis, B.; Bastien, N.; Ho, J.; Kobasa, D.; Stadnyk, L.; Li, Y.; Spence, M.; Paton, S.; Henry, B. Detection of Airborne Severe Acute Respiratory Syndrome (SARS) Coronavirus and Environmental Contamination in SARS Outbreak Units. J. Infect. Dis. 2005, 191 (9), 1472– 1477, DOI: 10.1086/429634[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2M7ns1Gqug%253D%253D&md5=6314670743c6b810394a8a6073242bc0Detection of airborne severe acute respiratory syndrome (SARS) coronavirus and environmental contamination in SARS outbreak unitsBooth Timothy F; Kournikakis Bill; Bastien Nathalie; Ho Jim; Kobasa Darwyn; Stadnyk Laurie; Li Yan; Spence Mel; Paton Shirley; Henry Bonnie; Mederski Barbara; White Diane; Low Donald E; McGeer Allison; Simor Andrew; Vearncombe Mary; Downey James; Jamieson Frances B; Tang Patrick; Plummer FrankThe Journal of infectious diseases (2005), 191 (9), 1472-7 ISSN:0022-1899.Severe acute respiratory syndrome (SARS) is characterized by a risk of nosocomial transmission; however, the risk of airborne transmission of SARS is unknown. During the Toronto outbreaks of SARS, we investigated environmental contamination in SARS units, by employing novel air sampling and conventional surface swabbing. Two polymerase chain reaction (PCR)-positive air samples were obtained from a room occupied by a patient with SARS, indicating the presence of the virus in the air of the room. In addition, several PCR-positive swab samples were recovered from frequently touched surfaces in rooms occupied by patients with SARS (a bed table and a television remote control) and in a nurses' station used by staff (a medication refrigerator door). These data provide the first experimental confirmation of viral aerosol generation by a patient with SARS, indicating the possibility of airborne droplet transmission, which emphasizes the need for adequate respiratory protection, as well as for strict surface hygiene practices.
- 9Herfst, S.; Schrauwen, E. J.; Linster, M. Airborne Transmission of Influenza A/H5N1 Virus between Ferrets. Science 2012, 336 (6088), 1534– 1541, DOI: 10.1126/science.1213362[Crossref], [PubMed], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xoslaksbw%253D&md5=19a11c8baf401ca29fade4b35b1c582dAirborne transmission of influenza A/H5N1 virus between ferretsHerfst, Sander; Schrauwen, Eefje J. A.; Linster, Martin; Chutinimitkul, Salin; de Wit, Emmie; Munster, Vincent J.; Sorrell, Erin M.; Bestebroer, Theo M.; Burke, David F.; Smith, Derek J.; Rimmelzwaan, Guus F.; Osterhaus, Albert D. M. E.; Fouchier, Ron A. M.Science (Washington, DC, United States) (2012), 336 (6088), 1534-1541CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Highly pathogenic avian influenza A/H5N1 virus can cause morbidity and mortality in humans but thus far has not acquired the ability to be transmitted by aerosol or respiratory droplet ("airborne transmission") between humans. To address the concern that the virus could acquire this ability under natural conditions, we genetically modified A/H5N1 virus by site-directed mutagenesis and subsequent serial passage in ferrets. The genetically modified A/H5N1 virus acquired mutations during passage in ferrets, ultimately becoming airborne transmissible in ferrets. None of the recipient ferrets died after airborne infection with the mutant A/H5N1 viruses. Four amino acid substitutions in the host receptor-binding protein hemagglutinin, and one in the polymerase complex protein basic polymerase 2, were consistently present in airborne-transmitted viruses. The transmissible viruses were sensitive to the antiviral drug oseltamivir and reacted well with antisera raised against H5 influenza vaccine strains. Thus, avian A/H5N1 influenza viruses can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host and therefore constitute a risk for human pandemic influenza.
- 10Ye, C.; Zhu, W.; Yu, J. Understanding the complex seasonality of seasonal influenza A and B virus transmission: Evidence from six years of surveillance data in Shanghai, China. Int. J. Infect. Dis. 2019, 81, 57– 65, DOI: 10.1016/j.ijid.2019.01.027[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB3cjlsFKgsw%253D%253D&md5=6f7da0e513d37f909fbc8c826022559aUnderstanding the complex seasonality of seasonal influenza A and B virus transmission: Evidence from six years of surveillance data in Shanghai, ChinaYe Chuchu; Zhu Weiping; Wang Yuanping; Gu Huozheng; Zou Wenwei; Yu Jianxing; Li Zhongjie; Zhang Yuzhou; Hao Lipeng; Hu WenbiaoInternational journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases (2019), 81 (), 57-65 ISSN:.OBJECTIVES: Understanding the complexity of influenza subtype seasonality is critical to promoting a suitable vaccination program. The aim of this study was to identify and compare the seasonality and epidemiological features of seasonal influenza subtypes after the 2009 A/H1N1 pandemic and to lay a foundation for further investigation into the social and environmental factors affecting seasonal influenza virus transmission. METHODS: Influenza-like illness (ILI) case surveillance was conducted in two sentinel hospitals in Pudong New Area, Shanghai between 2012 and 2018. Weekly data on ILI cases were analyzed. A time-series seasonal decomposition analysis was used to reveal the seasonality of influenza and epidemiological features among different subtypes. RESULTS: In total, 10977 ILI patients were enrolled of whom 2385 (21.7%) had laboratory-confirmed influenza. Compared to influenza A (16.3%), influenza B (5.4%) was less frequently detected among the ILI patients (p<0.001). Semiannual epidemic peaks were identified in four of the years during the 6-year study period, while only one annual epidemic peak was found in the other two years. An epidemic peak occurred in each winter season, and a secondary peak also occasionally occurred in summer or spring. A/H3N2 predominated in both summer and winter, while A/H1N1, B/Yamagata, and B/Victoria circulated almost exclusively in winter or spring. Two lineages of influenza B seemed to predominate in alternating years. CONCLUSIONS: This study highlights the complexity of seasonal influenza virus activity in a subtropical region of China, presenting both semiannual and annual epidemic peaks in different years. The results of this study may provide further insight into possible improvements in the timing of influenza vaccination in Shanghai, China.
- 11Lofgren, E.; Fefferman, N. H.; Naumov, Y. N.; Gorski, J.; Naumova, E. N. Influenza seasonality: underlying causes and modeling theories. J. Virol. 2007, 81 (11), 5429– 5436, DOI: 10.1128/JVI.01680-06[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmtFGlt7g%253D&md5=4df6ce502bada95908fcc738c9f24921Influenza seasonality: underlying causes and modeling theoriesLofgren, Eric; Fefferman, N. H.; Naumov, Y. N.; Gorski, J.; Naumova, E. N.Journal of Virology (2007), 81 (11), 5429-5436CODEN: JOVIAM; ISSN:0022-538X. (American Society for Microbiology)There is no expanded citation for this reference.
- 12Likhacheva, A. SARS Revisited. AMA J. Ethics 2006, 8 (4), 219– 222
- 13Lipsitch, M. Seasonality of SARS-CoV-2: Will COVID-19 go away on its own in warmer weather? https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-own-in-warmer-weather/ (accessed 2020-05-03).Google ScholarThere is no corresponding record for this reference.
- 14Lowen, A. C.; Steel, J. Roles of humidity and temperature in shaping influenza seasonality. J. Virol. 2014, 88 (14), 7692– 7695, DOI: 10.1128/JVI.03544-13[Crossref], [PubMed], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsVKjtbbK&md5=f3c79f190ec631fddb3b7d788cf7f4f9Roles of humidity and temperature in shaping influenza seasonalityLowen, Anice C.; Steel, JohnJournal of Virology (2014), 88 (14), 7692-7695, 5 pp.CODEN: JOVIAM; ISSN:1098-5514. (American Society for Microbiology)Exptl. studies in guinea pigs demonstrated that influenza virus transmission is strongly modulated by temp. and humidity. A no. of epidemiol. studies have followed up on these findings and revealed robust assocns. between influenza incidence in temperate regions and local conditions of humidity and temp., offering a long-awaited explanation for the wintertime seasonality of influenza in these locales. Despite recent progress, important questions remain as to the mechanism(s) by which humidity and/or temp. affects transmission.
- 15Chan, K. H.; Peiris, J. S. M.; Lam, S. Y.; Poon, L. L. M.; Yuen, K. Y.; Seto, W. H. The effects of temperature and relative humidity on the viability of the SARS coronavirus. Adv. Virol. 2011, 2011 (734690), 1– 7, DOI: 10.1155/2011/734690
- 16Bourouiba, L. Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19. JAMA 2020, 323 (18), 1837– 1838, DOI: 10.1001/jama.2020.4756[Crossref], [PubMed], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383nslKqtg%253D%253D&md5=e240ace69fbf2eebd3446aa623e9c556Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19Bourouiba LydiaJAMA (2020), 323 (18), 1837-1838 ISSN:.There is no expanded citation for this reference.
- 17Mittal, R.; Ni, R.; Seo, J.-H. The Flow Physics of COVID-19. J. Fluid Mech. 2020, 894, 894, DOI: 10.1017/jfm.2020.330
- 18Scharfman, B. E.; Techet, A. H.; Bush, J. W. M.; Bourouiba, L. Visualization of Sneeze Ejecta: Steps of Fluid Fragmentation Leading to Respiratory Droplets. Exp. Fluids 2016, 57 (2), 24, DOI: 10.1007/s00348-015-2078-4[Crossref], [PubMed], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383ns1Olsg%253D%253D&md5=d1ff8e6d9059aec4895a3799c47b0959Visualization of sneeze ejecta: steps of fluid fragmentation leading to respiratory dropletsScharfman B E; Techet A H; Bush J W M; Bourouiba LExperiments in fluids (2016), 57 (2), 24 ISSN:0723-4864.Coughs and sneezes feature turbulent, multiphase flows that may contain pathogen-bearing droplets of mucosalivary fluid. As such, they can contribute to the spread of numerous infectious diseases, including influenza and SARS. The range of contamination of the droplets is largely determined by their size. However, major uncertainties on the drop size distributions persist. Here, we report direct observation of the physical mechanisms of droplet formation at the exit of the mouth during sneezing. Specifically, we use high-speed imaging to directly examine the fluid fragmentation at the exit of the mouths of healthy subjects. We reveal for the first time that the breakup of the fluid into droplets continues to occur outside of the respiratory tract during violent exhalations. We show that such breakup involves a complex cascade of events from sheets, to bag bursts, to ligaments, which finally break into droplets. Finally, we reveal that the viscoelasticity of the mucosalivary fluid plays an important role in delaying fragmentation by causing the merger of the droplet precursors that form along stretched filaments; thereby affecting the final drop size distribution farther downstream.
- 19Chin, A.; Chu, J.; Perera, M.; Hui, K.; Yen, H.-L.; Chan, M.; Peiris, M.; Poon, L. Stability of SARS-CoV-2 in Different Environmental Conditions. Lancet Microbe 2020, 1 (1), e10 DOI: 10.1016/S2666-5247(20)30003-3[Crossref], [PubMed], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXit1Kms7%252FJ&md5=933fd5dff634c6f2bd88095b1ef316fcStability of SARS-CoV-2 in different environmental conditionsChin, Alex W. H.; Chu, Julie T. S.; Perera, Mahen R. A.; Hui, Kenrie P. Y.; Yen, Hui-Ling; Chan, Michael C. W.; Peiris, Malik; Poon, Leo L. M.Lancet Microbe (2020), 1 (1), e10CODEN: LMAIAR; ISSN:2666-5247. (Elsevier Ltd.)There is no expanded citation for this reference.
- 20van Doremalen, N.; Bushmaker, T.; Morris, D. H.; Holbrook, M. G.; Gamble, A.; Williamson, B. N.; Tamin, A.; Harcourt, J. L.; Thornburg, N. J.; Gerber, S. I. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N. Engl. J. Med. 2020, 382 (16), 1564– 1567, DOI: 10.1056/NEJMc2004973[Crossref], [PubMed], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383ksVKktw%253D%253D&md5=9803ae46c83b19c312f0d810c975378eAerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1van Doremalen Neeltje; Bushmaker Trenton; Holbrook Myndi G; Williamson Brandi N; de Wit Emmie; Munster Vincent J; Morris Dylan H; Gamble Amandine; Tamin Azaibi; Harcourt Jennifer L; Thornburg Natalie J; Gerber Susan I; Lloyd-Smith James OThe New England journal of medicine (2020), 382 (16), 1564-1567 ISSN:.There is no expanded citation for this reference.
- 21Fears, A. C.; Klimstra, W. B.; Duprex, P.; Hartman, A. Comparative Dynamic Aerosol Efficiencies of Three Emergent Coronaviruses and the Unusual Persistence of SARS-CoV-2 in Aerosol Suspensions. medRxiv, 2020, 2020.04.13.20063784. DOI: 10.1101/2020.04.13.20063784v1 (accessed 2020-05-04).
- 22Stadnytskyi, V.; Bax, C. E.; Bax, A.; Anfinrud, P. The Airborne Lifetime of Small Speech Droplets and Their Potential Importance in SARS-CoV-2 Transmission. Proc. Natl. Acad. Sci. U. S. A. 2020, 117 (22), 11875– 11877, DOI: 10.1073/pnas.2006874117[Crossref], [PubMed], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtlSltrzI&md5=e553c69851fc1afc32e617ccd7be00f9The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmissionStadnytskyi, Valentyn; Bax, Christina E.; Bax, AdriaanProceedings of the National Academy of Sciences of the United States of America (2020), 117 (22), 11875-11877CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)Speech droplets generated by asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are increasingly considered to be a likely mode of disease transmission. Highly sensitive laser light scattering observations have revealed that loud speech can emit thousands of oral fluid droplets per s. In a closed, stagnant air environment, they disappear from the window of view with time consts. in the range of 8 to 14 min, which corresponds to droplet nuclei of ca. 4μm diam., or 12- to 21-μm droplets prior to dehydration. These observations confirm that there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.
- 23Xie, X.; Li, Y.; Sun, H.; Liu, L. Exhaled Droplets Due to Talking and Coughing. J. R. Soc., Interface 2009, 6, S703– S714, DOI: 10.1098/rsif.2009.0388.focus
- 24Cole, E. C.; Cook, C. E. Characterization of Infectious Aerosols in Health Care Facilities: An Aid to Effective Engineering Controls and Preventive Strategies. Am. J. Infect. Control 1998, 26 (4), 453– 464, DOI: 10.1016/S0196-6553(98)70046-X[Crossref], [PubMed], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADyaK1czovVaqsg%253D%253D&md5=9cab0801c49e70f15609fa166b3640d6Characterization of infectious aerosols in health care facilities: an aid to effective engineering controls and preventive strategiesCole E C; Cook C EAmerican journal of infection control (1998), 26 (4), 453-64 ISSN:0196-6553.Assessment of strategies for engineering controls for the prevention of airborne infectious disease transmission to patients and to health care and related workers requires consideration of the factors relevant to aerosol characterization. These factors include aerosol generation, particle size and concentrations, organism viability, infectivity and virulence, airflow and climate, and environmental sampling and analysis. The major focus on attention to engineering controls comes from recent increases in tuberculosis, particularly the multidrug-resistant varieties in the general hospital population, the severely immunocompromised, and those in at-risk and confined environments such as prisons, long-term care facilities, and shelters for the homeless. Many workers are in close contact with persons who have active, undiagnosed, or insufficiently treated tuberculosis. Additionally, patients and health care workers may be exposed to a variety of pathogenic human viruses, opportunistic fungi, and bacteria. This report therefore focuses on the nature of infectious aerosol transmission in an attempt to determine which factors can be systematically addressed to result in proven, applied engineering approaches to the control of infectious aerosols in hospital and health care facility environments. The infectious aerosols of consideration are those that are generated as particles of respirable size by both human and environmental sources and that have the capability of remaining viable and airborne for extended periods in the indoor environment. This definition precludes skin and mucous membrane exposures occurring from splashes (rather than true aerosols) of blood or body fluids containing infectious disease agents. There are no epidemiologic or laboratory studies documenting the transmission of bloodborne virus by way of aerosols.
- 25Chao, C. Y. H.; Wan, M. P.; Morawska, L.; Johnson, G. R.; Ristovski, Z. D.; Hargreaves, M.; Mengersen, K.; Corbett, S.; Li, Y.; Xie, X.; Katoshevski, D. Characterization of expiration air jets and droplet size distributions immediately at the mouth opening. J. Aerosol Sci. 2009, 40 (2), 122– 133, DOI: 10.1016/j.jaerosci.2008.10.003[Crossref], [PubMed], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtFSns7Y%253D&md5=6f35010e4b5a1f48b02026c888d637a4Characterization of expiration air jets and droplet size distributions immediately at the mouth openingChao, C. Y. H.; Wan, M. P.; Morawska, L.; Johnson, G. R.; Ristovski, Z. D.; Hargreaves, M.; Mengersen, K.; Corbett, S.; Li, Y.; Xie, X.; Katoshevski, D.Journal of Aerosol Science (2009), 40 (2), 122-133CODEN: JALSB7; ISSN:0021-8502. (Elsevier Ltd.)Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The av. expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the exptl. setting, evapn. and condensation effects had negligible impact on the measured droplet size. The geometric mean diam. of droplets from coughing was 13.5 μm and it was 16.0 μm for speaking (counting 1-100). The estd. total no. of droplets expelled ranged from 947 to 2085 per cough and 112-6720 for speaking. The estd. droplet concns. for coughing ranged from 2.4 to 5.2 cm-3 per cough and 0.004-0.223 cm-3 for speaking.
- 26Xie, X.; Li, Y.; Chwang, A.; Ho, P.; Seto, W. How Far Droplets Can Move in Indoor Environments–Revisiting the Wells Evaporation-Falling Curve. Indoor Air 2007, 17 (3), 211– 225, DOI: 10.1111/j.1600-0668.2007.00469.x[Crossref], [PubMed], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2szjtFOrtw%253D%253D&md5=a751500d0142e767d36726d35204e03bHow far droplets can move in indoor environments--revisiting the Wells evaporation-falling curveXie X; Li Y; Chwang A T Y; Ho P L; Seto W HIndoor air (2007), 17 (3), 211-25 ISSN:0905-6947.UNLABELLED: A large number of infectious diseases are believed to be transmitted between people via large droplets and by airborne routes. An understanding of evaporation and dispersion of droplets and droplet nuclei is not only significant for developing effective engineering control methods for infectious diseases but also for exploring the basic transmission mechanisms of the infectious diseases. How far droplets can move is related to how far droplet-borne diseases can transmit. A simple physical model is developed and used here to investigate the evaporation and movement of droplets expelled during respiratory activities; in particular, the well-known Wells evaporation-falling curve of droplets is revisited considering the effect of relative humidity, air speed, and respiratory jets. Our simple model considers the movement of exhaled air, as well as the evaporation and movement of a single droplet. Exhaled air is treated as a steady-state non-isothermal (warm) jet horizontally issuing into stagnant surrounding air. A droplet is assumed to evaporate and move in this non-isothermal jet. Calculations are performed for both pure water droplets and droplets of sodium chloride (physiological saline) solution (0.9% w/v). We calculate the droplet lifetimes and how droplet size changes, as well as how far the droplets travel in different relative humidities. Our results indicate that a droplet's size predominately dictates its evaporation and movement after being expelled. The sizes of the largest droplets that would totally evaporate before falling 2 m away are determined under different conditions. The maximum horizontal distances that droplets can reach during different respiratory activities are also obtained. Our study is useful for developing effective prevention measures for controlling infectious diseases in hospitals and in the community at large. PRACTICAL IMPLICATIONS: Our study reveals that for respiratory exhalation flows, the sizes of the largest droplets that would totally evaporate before falling 2 m away are between 60 and 100 microm, and these expelled large droplets are carried more than 6 m away by exhaled air at a velocity of 50 m/s (sneezing), more than 2 m away at a velocity of 10 m/s (coughing) and less than 1 m away at a velocity of 1 m/s (breathing). These findings are useful for developing effective engineering control methods for infectious diseases, and also for exploring the basic transmission mechanisms of the infectious diseases. There is a need to examine the air distribution systems in hospital wards for controlling both airborne and droplet-borne transmitted diseases.
- 27Gralton, J.; Tovey, E.; McLaws, M.-L.; Rawlinson, W. D. The Role of Particle Size in Aerosolised Pathogen Transmission: A Review. J. Infect. 2011, 62 (1), 1– 13, DOI: 10.1016/j.jinf.2010.11.010[Crossref], [PubMed], [CAS], Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3M7islWksw%253D%253D&md5=eace75d8f8710c153e501d1fbea4f55fThe role of particle size in aerosolised pathogen transmission: a reviewGralton Jan; Tovey Euan; McLaws Mary-Louise; Rawlinson William DThe Journal of infection (2011), 62 (1), 1-13 ISSN:.Understanding respiratory pathogen transmission is essential for public health measures aimed at reducing pathogen spread. Particle generation and size are key determinant for pathogen carriage, aerosolisation, and transmission. Production of infectious respiratory particles is dependent on the type and frequency of respiratory activity, type and site of infection and pathogen load. Further, relative humidity, particle aggregation and mucus properties influence expelled particle size and subsequent transmission. Review of 26 studies reporting particle sizes generated from breathing, coughing, sneezing and talking showed healthy individuals generate particles between 0.01 and 500 μm, and individuals with infections produce particles between 0.05 and 500 μm. This indicates that expelled particles carrying pathogens do not exclusively disperse by airborne or droplet transmission but avail of both methods simultaneously and current dichotomous infection control precautions should be updated to include measures to contain both modes of aerosolised transmission.
- 28Kormuth, K. A.; Lin, K.; Prussin, A. J.; Vejerano, E. P.; Tiwari, A. J.; Cox, S. S.; Myerburg, M. M.; Lakdawala, S. S.; Marr, L. C. Influenza Virus Infectivity Is Retained in Aerosols and Droplets Independent of Relative Humidity. J. Infect. Dis. 2018, 218 (5), 739– 747, DOI: 10.1093/infdis/jiy221[Crossref], [PubMed], [CAS], Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtlCntrfF&md5=2043db121617b8256bd6275904900984Influenza virus infectivity is retained in aerosols and droplets independent of relative humidityKormuth, Karen A.; Lin, Kaisen; Prussin, Aaron J., II; Vejerano, Eric P.; Tiwari, Andrea J.; Cox, Steve S.; Myerburg, Michael M.; Lakdawala, Seema S.; Marr, Linsey C.Journal of Infectious Diseases (2018), 218 (5), 739-747CODEN: JIDIAQ; ISSN:1537-6613. (Oxford University Press)Pandemic and seasonal influenza viruses can be transmitted through aerosols and droplets, in which viruses must remain stable and infectious across a wide range of environmental conditions. Using humidity-controlled chambers, we studied the impact of relative humidity on the stability of 2009 pandemic influenza A(H1N1) virus in suspended aerosols and stationary droplets. Contrary to the prevailing paradigm that humidity modulates the stability of respiratory viruses in aerosols, we found that viruses supplemented with material from the apical surface of differentiated primary human airway epithelial cells remained equally infectious for 1 h at all relative humidities tested. This sustained infectivity was obsd. in both fine aerosols and stationary droplets. Our data suggest, for the first time, that influenza viruses remain highly stable and infectious in aerosols across a wide range of relative humidities. These results have significant implications for understanding the mechanisms of transmission of influenza and its seasonality.
- 29Chen, C.; Zhao, B. Some questions on dispersion of human exhaled droplets in ventilation room: answers from numerical investigation. Indoor Air 2010, 20 (2), 95– 111, DOI: 10.1111/j.1600-0668.2009.00626.x[Crossref], [PubMed], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3c3nvVSlsQ%253D%253D&md5=649cbe46d55865ef0c4aa8cfdd151ab2Some questions on dispersion of human exhaled droplets in ventilation room: answers from numerical investigationChen C; Zhao BIndoor air (2010), 20 (2), 95-111 ISSN:.This study employs a numerical model to investigate the dispersion characteristics of human exhaled droplets in ventilation rooms. The numerical model is validated by two different experiments prior to the application for the studied cases. Some typical questions on studying dispersion of human exhaled droplets indoors are reviewed and numerical study using the normalized evaporation time and normalized gravitational sedimentation time was performed to obtain the answers. It was found that modeling the transient process from a droplet to a droplet nucleus due to evaporation can be neglected when the normalized evaporation time is <0.051. When the normalized gravitational sedimentation time is <0.005, the influence of ventilation rate could be neglected. However, the influence of ventilation pattern and initial exhaled velocity on the exhaled droplets dispersion is dominant as the airflow decides the droplets dispersion significantly. Besides, the influence of temperature and relative humidity on the dispersion of droplets can be neglected for the droplet with initial diameter <200 microm; while droplet nuclei size plays an important role only for the droplets with initial diameter within the range of 10 microm-100 microm. Practical Implications Dispersion of human exhaled droplets indoor is a key issue when evaluating human exposure to infectious droplets. Results from detailed numerical studies in this study reveal how the evaporation of droplets, ventilation rate, airflow pattern, initial exhaled velocity, and particle component decide the droplet dispersion indoor. The detailed analysis of these main influencing factors on droplet dispersion in ventilation rooms may help to guide (1) the selection of numerical approach, e.g., if the transient process from a droplet to a droplet nucleus due to evaporation should be incorporated to study droplet dispersion, and (2) the selection of ventilation system to minimize the spread of pathogen-laden droplets in an indoor environment.
- 30Mui, K. W.; Wong, L. T.; Wu, C. L.; Lai, A. C. Numerical modeling of exhaled droplet nuclei dispersion and mixing in indoor environments. J. Hazard. Mater. 2009, 167 (1–3), 736– 744, DOI: 10.1016/j.jhazmat.2009.01.041[Crossref], [PubMed], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXmt1Giu7c%253D&md5=1bd81bc9fbcceb99b0513120bfb2e779Numerical modeling of exhaled droplet nuclei dispersion and mixing in indoor environmentsMui, K. W.; Wong, L. T.; Wu, C. L.; Lai, Alvin C. K.Journal of Hazardous Materials (2009), 167 (1-3), 736-744CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)The increasing incidence of indoor airborne infections has prompted attention upon the investigation of expiratory droplet dispersion and transport in built environments. In this study, a source (i.e. a patient who generates droplets) and a receiver (i.e. a susceptible object other than the source) are modeled in a mech. ventilated room. The receiver's exposure to the droplet nuclei is analyzed under two orientations relative to the source. Two droplet nuclei, 0.1 and 10 μm, with different emission velocities, are selected to represent large expiratory droplets which can still be inhaled into the human respiratory tracts. The droplet dispersion and mixing characteristics under well-mixed and displacement ventilation schemes are evaluated and compared numerically. Results show that the droplet dispersion and mixing under displacement ventilation is consistently poorer. Very low concn. regions are also obsd. in the displacement scheme. For both ventilation schemes, the intake dose will be reduced substantially if the droplets are emitted under the face-to-wall orientation rather than the face-to-face orientation. Implications of using engineering strategies for reducing exposure are briefly discussed.
- 31Ai, Z. T.; Melikov, A. K. Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A review. Indoor Air 2018, 28 (4), 500– 524, DOI: 10.1111/ina.12465[Crossref], [PubMed], [CAS], Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1MjlsVOqtQ%253D%253D&md5=1d3c98a32cd8da6fcac847964f281201Airborne spread of expiratory droplet nuclei between the occupants of indoor environments: A reviewAi Z T; Melikov A KIndoor air (2018), 28 (4), 500-524 ISSN:.This article reviews past studies of airborne transmission between occupants in indoor environments, focusing on the spread of expiratory droplet nuclei from mouth/nose to mouth/nose for non-specific diseases. Special attention is paid to summarizing what is known about the influential factors, the inappropriate simplifications of the thermofluid boundary conditions of thermal manikins, the challenges facing the available experimental techniques, and the limitations of available evaluation methods. Secondary issues are highlighted, and some new ways to improve our understanding of airborne transmission indoors are provided. The characteristics of airborne spread of expiratory droplet nuclei between occupants, which are influenced correlatively by both environmental and personal factors, were widely revealed under steady-state conditions. Owing to the different boundary conditions used, some inconsistent findings on specific influential factors have been published. The available instrumentation was too slow to provide accurate concentration profiles for time-dependent evaluations of events with obvious time characteristics, while computational fluid dynamics (CFD) studies were mainly performed in the framework of inherently steady Reynolds-averaged Navier-Stokes modeling. Future research needs in 3 areas are identified: the importance of the direction of indoor airflow patterns, the dynamics of airborne transmission, and the application of CFD simulations.
- 32Nicas, M.; Best, D. A Study Quantifying the Hand-to-Face Contact Rate and Its Potential Application to Predicting Respiratory Tract Infection. J. Occup. Environ. Hyg. 2008, 5 (6), 347– 352, DOI: 10.1080/15459620802003896[Crossref], [PubMed], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD1c7pvVerug%253D%253D&md5=e32c53a0e57143adad9efb2d449f5ed0A study quantifying the hand-to-face contact rate and its potential application to predicting respiratory tract infectionNicas Mark; Best DanielJournal of occupational and environmental hygiene (2008), 5 (6), 347-52 ISSN:.A substantial portion of human respiratory tract infection is thought to be transmitted via contaminated hand contact with the mouth, eyes, and/or nostrils. Thus, a key risk factor for infection transmission should be the rate of hand contact with these areas termed target facial membranes. A study was conducted in which 10 subjects were each videotaped for 3 hr while performing office-type work in isolation from other persons. The number of contacts to the eyes, nostrils, and lips was scored during subsequent viewing of the tapes. The total contacts per subject had sample mean x = 47 and sample standard deviation s = 34. The average total contact rate per hour was 15.7. The authors developed a relatively simple algebraic model for estimating the dose of pathogens transferred to target facial membranes during a defined exposure period. The model considers the rate of pathogen transfer to the hands via contact with contaminated environmental surfaces, and the rate of pathogen loss from the hands due to pathogen die-off and transfer from the hands to environmental surfaces and to target facial membranes during touching. The estimation of infection risk due to this dose also is discussed. A hypothetical but plausible example involving influenza A virus transmission is presented to illustrate the model.
- 33Nicas, M.; Sun, G. An Integrated Model of Infection Risk in a Health-Care Environment. Risk Anal 2006, 26 (4), 1085– 1096, DOI: 10.1111/j.1539-6924.2006.00802.x[Crossref], [PubMed], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD28rislaqsw%253D%253D&md5=0ab91b4ffc0c419d60891cea1d00bf38An integrated model of infection risk in a health-care environmentNicas Mark; Sun GangRisk analysis : an official publication of the Society for Risk Analysis (2006), 26 (4), 1085-96 ISSN:0272-4332.Certain respiratory tract infections can be transmitted by hand-to-mucous-membrane contact, inhalation, and/or direct respiratory droplet spray. In a room occupied by a patient with such a transmissible infection, pathogens present on textile and nontextile surfaces, and pathogens present in the air, provide sources of exposure for an attending health-care worker (HCW); in addition, close contact with the patient when the latter coughs allows for droplet spray exposure. We present an integrated model of pertinent source-environment-receptor pathways, and represent physical elements in these pathways as "states" in a discrete-time Markov chain model. We estimate the rates of transfer at various steps in the pathways, and their relationship to the probability that a pathogen in one state has moved to another state by the end of a specified time interval. Given initial pathogen loads on textile and nontextile surfaces and in room air, we use the model to estimate the expected pathogen dose to a HCW's mucous membranes and respiratory tract. In turn, using a nonthreshold infectious dose model, we relate the expected dose to infection risk. The system is illustrated with a hypothetical but plausible scenario involving a viral pathogen emitted via coughing. We also use the model to show that a biocidal finish on textile surfaces has the potential to substantially reduce infection risk via the hand-to-mucous-membrane exposure pathway.
- 34Tellier, R. Aerosol Transmission of Influenza A Virus: A Review of New Studies. J. R. Soc., Interface 2009, 6, S783– S790, DOI: 10.1098/rsif.2009.0302.focus
- 35Wells, W. On Air-Borne Infection: Study II. Droplets and Droplet Nuclei. Am. J. Epidemiol. 1934, 20 (3), 611– 618, DOI: 10.1093/oxfordjournals.aje.a118097
- 36Kukkonen, J.; Vesala, T.; Kulmala, M. The Interdependence of Evaporation and Settling for Airborne Freely Falling Droplets. J. Aerosol Sci. 1989, 20 (7), 749– 763, DOI: 10.1016/0021-8502(89)90087-6[Crossref], [CAS], Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3cXmtFOiurY%253D&md5=72d34039a0bc8188d34ceca2d30ce645The interdependence of evaporation and settling for airborne freely falling dropletsKukkonen, J.; Vesala, T.; Kulmala, M.Journal of Aerosol Science (1989), 20 (7), 749-63CODEN: JALSB7; ISSN:0021-8502.The results are presented of theor. investigations concerning the quasistationary evapn. of freely falling droplets in the continuum regime. The math. model is based on the simultaneous numerical soln. of the equations governing mass and heat transfer from the droplet surfaces. The model includes a description of forced convective mass and heat transfer due to free fall. The investigation were focused on estg. the effect of the competing evapn. and settling processes on the deposition of a population of monodisperse droplets. The model was applied to predict the evolution of water and NH3 droplets in gas mixts. contg. air and the vapor of evapg. species.
- 37World Health Organization. Infection Prevention and Control of Epidemic-and Pandemic-Prone Acute Respiratory Infections in Health Care. https://www.who.int/csr/bioriskreduction/infection_control/publication/en/ (accessed 2020-05-05).Google ScholarThere is no corresponding record for this reference.
- 38Alsved, M.; Bourouiba, L.; Duchaine, C.; Löndahl, J.; Marr, L. C.; Parker, S. T.; Prussin, A. J.; Thomas, R. J. Natural Sources and Experimental Generation of Bioaerosols: Challenges and Perspectives. Aerosol Sci. Technol. 2020, 54 (5), 547– 571, DOI: 10.1080/02786826.2019.1682509[Crossref], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitFamsLjE&md5=eefcc3a6edf17af5858082a473da133cNatural sources and experimental generation of bioaerosols: Challenges and perspectivesAlsved, Malin; Bourouiba, Lydia; Duchaine, Caroline; Loendahl, Jakob; Marr, Linsey C.; Parker, Simon T.; Prussin, Aaron J. II; Thomas, Richard J.Aerosol Science and Technology (2020), 54 (5), 547-571CODEN: ASTYDQ; ISSN:0278-6826. (Taylor & Francis, Inc.)A review. Exptl. aerosol generation methods aim to represent natural processes; however, the complexity is not always captured and unforeseen variability may be introduced into the data. The current practices for natural and exptl. aerosol generation techniques are reviewed here. Recommendations for best practice are presented, and include characterization of starting material and spray fluid, rational selection of appropriate aerosol generators, and phys. and biol. characterization of the output aerosol. Reporting of bioaerosol research should capture sufficient detail to aid data interpretation, reduce variation, and facilitate comparison between research labs. Finally, future directions and challenges in bioaerosol generation are discussed.
- 39Poulain, S.; Bourouiba, L. Disease Transmission via Drops and Bubbles. Phys. Today 2019, 72 (5), 70– 71, DOI: 10.1063/PT.3.4211
- 40Kwon, S.-B.; Park, J.; Jang, J.; Cho, Y.; Park, D.-S.; Kim, C.; Bae, G.-N.; Jang, A. Study on the Initial Velocity Distribution of Exhaled Air from Coughing and Speaking. Chemosphere 2012, 87 (11), 1260– 1264, DOI: 10.1016/j.chemosphere.2012.01.032[Crossref], [PubMed], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XisFKitr8%253D&md5=52ca235530f50921480dd7426f2cceb7Study on the initial velocity distribution of exhaled air from coughing and speakingKwon, Soon-Bark; Park, Jaehyung; Jang, Jaeyoun; Cho, Youngmin; Park, Duck-Shin; Kim, Changsoo; Bae, Gwi-Nam; Jang, AmChemosphere (2012), 87 (11), 1260-1264CODEN: CMSHAF; ISSN:0045-6535. (Elsevier Ltd.)Increasing concerns about the spread of airborne pathogens such as severe acute respiratory syndrome (SARS) and novel swine-origin influenza A (H1N1) have attracted public attention to bioaerosols and protection against them. The airborne pathogens are likely to be expelled from coughing or speaking, so the phys. data of the exhaled particles plays a key role in analyzing the pathway of airborne viruses. The objective of this study was to analyze the initial velocity and the angle of the exhaled airflow from coughing and speaking of 17 males and 9 females using Particle Image Velocimetry (PIV) and acrylic indoor chamber. The results showed that the av. initial coughing velocity was 15.3 m/s for the males and 10.6 m/s for the females, while the av. initial speaking velocity was 4.07 m/s and 2.31 m/s resp. The angle of the exhaled air from coughing was around 38° for the males and 32° for the females, while that of the exhaled air from speaking was around 49° and 78° resp. Also, the linear relation between the tested subject's height and their coughing and speaking velocity was shown in this study.
- 41Duguid, J. P. The Size and the Duration of Air-Carriage of Respiratory Droplets and Droplet-Nuclei. Epidemiol. Infect. 1946, 44 (6), 471– 479, DOI: 10.1017/S0022172400019288
- 42Höppe, P. Temperatures of Expired Air under Varying Climatic Conditions. Int. J. Biometeorol. 1981, 25 (2), 127– 132, DOI: 10.1007/BF02184460[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADyaL3M3jvVyjsA%253D%253D&md5=fb9629dca876a9dafbfdec9da9b48774Temperatures of expired air under varying climate conditionsHoppe PInternational journal of biometeorology (1981), 25 (2), 127-32 ISSN:0020-7128.There is no expanded citation for this reference.
- 43Baldwin, P. E.; Maynard, A. D. A Survey of Wind Speeds in Indoor Workplaces. Ann. Occup. Hyg. 1998, 42 (5), 303– 313, DOI: 10.1016/S0003-4878(98)00031-3[Crossref], [PubMed], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXmtVOqsbo%253D&md5=c7830bfc22fe5491cc905c25bb3fe3d2A survey of wind speeds in indoor workplacesBaldwin, Peter E. J.; Maynard, Andrew D.Annals of Occupational Hygiene (1998), 42 (5), 303-313CODEN: AOHYA3; ISSN:0003-4878. (Elsevier Science Ltd.)The applicability of the inhalable convention for sampling aerosols relies on its being a valid model for typical sampling environments. The current convention is based on measurements carried out in external wind speeds between 1 and 4 m·s-1. However these measurements show a degree of wind speed dependence, and it is uncertain at present how valid the convention is for describing human aspiration efficiency outside these wind speed limits. Following concerns that wind speeds in many indoor workplaces may be significantly below this range, measurements have been made in 55 work areas covering a wide range of workplaces. Measurements have concd. on "background" wind speeds where the influence of specific air movement sources is minimized. The pooled wind speed measurements show a highly skewed distribution with an arithmetic mean of approx. 0.3 m·s-1. Approx. 85% of all individual measurements were below this mean value. No obvious correlation was found between wind speed distribution parameters and industry type, room size or ventilation type. A limited no. of comparisons were made between static anemometers and devices mounted on workers. It was found that modal wind speeds experience by workers were typically 0.05 m·s-1 higher than those measured using a static anemometer. These measurements agreed well with previously published data for similar workplaces as well as houses.
- 44Hoyt, T.; Arens, E.; Zhang, H. Extending air temperature setpoints: Simulated energy savings and design considerations for new and retrofit buildings. Build. Environ. 2015, 88, 89– 96, DOI: 10.1016/j.buildenv.2014.09.010
- 45Vejerano, E. P.; Marr, L. C. Physico-Chemical Characteristics of Evaporating Respiratory Fluid Droplets. J. R. Soc., Interface 2018, 15 (139), 20170939, DOI: 10.1098/rsif.2017.0939[Crossref], [PubMed], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFyksrbJ&md5=de2a7595c5481ed9943716c8d53c475aPhysico-chemical characteristics of evaporating respiratory fluid dropletsVejerano, Eric P.; Marr, Linsey C.Journal of the Royal Society, Interface (2018), 15 (139), 20170939/1-20170939/10CODEN: JRSICU; ISSN:1742-5662. (Royal Society)The detailed physico-chem. characteristics of respiratory droplets in ambient air, where they are subject to evapn., are poorly understood. Changes in the concn. and phase of major components in a droplet-salt (NaCl), protein (mucin) and surfactant (dipalmitoylphosphatidylcholine)-may affect the viability of any pathogens contained within it and thus may affect the efficiency of transmission of infectious disease by droplets and aerosols. The objective of this study is to investigate the effect of relative humidity (RH) on the physico-chem. characteristics of evapg. droplets of model respiratory fluids. We labeled these components in model respiratory fluids and obsd. evapg. droplets suspended on a superhydrophobic surface using optical and fluorescence microscopy. When exposed to continuously decreasing RH, droplets of different model respiratory fluids assumed different morphologies. Loss of water induced phase sepn. as well as indication of a decrease in pH. The presence of surfactant inhibited the rapid rehydration of the non-volatile components. An enveloped virus, φ6, that has been proposed as a surrogate for influenza virus appeared to be homogeneously distributed throughout the dried droplet. We hypothesize that the increasing acidity and salinity in evapg. respiratory droplets may affect the structure of the virus, although at low enough RH, crystn. of the droplet components may eliminate their harmful effects.
- 46Bahl, P.; Doolan, C.; de Silva, C.; Chughtai, A. A.; Bourouiba, L.; MacIntyre, C. R. Airborne or Droplet Precautions for Health Workers Treating COVID-19?. J. Infect. Dis. 2020, DOI: 10.1093/infdis/jiaa189
- 47Shakya, K. M.; Noyes, A.; Kallin, R.; Peltier, R. E. Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure. J. Exposure Sci. Environ. Epidemiol. 2017, 27 (3), 352– 357, DOI: 10.1038/jes.2016.42[Crossref], [PubMed], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhtl2mt7bO&md5=fc3dbb5a4b0b5b5e7985c9917e889140Evaluating the efficacy of cloth facemasks in reducing particulate matter exposureShakya, Kabindra M.; Noyes, Alyssa; Kallin, Randa; Peltier, Richard E.Journal of Exposure Science & Environmental Epidemiology (2017), 27 (3), 352-357CODEN: JESEBS; ISSN:1559-0631. (Nature Publishing Group)Inexpensive cloth masks are widely used in developing countries to protect from particulate pollution albeit limited data on their efficacy exists. This study examd. the efficiency of four types of masks (three types of cloth masks and one type of surgical mask) commonly worn in the developing world. Five monodispersed aerosol sphere size (30, 100, and 500 nm, and 1 and 2.5 μm) and dild. whole diesel exhaust was used to assess facemask performance. Among the three cloth mask types, a cloth mask with an exhaust valve performed best with filtration efficiency of 80-90% for the measured polystyrene latex (PSL) particle sizes. Two styles of com. available fabric masks were the least effective with a filtration efficiency of 39-65% for PSL particles, and they performed better as the particle size increased. When the cloth masks were tested against lab-generated whole diesel particles, the filtration efficiency for three particle sizes (30, 100, and 500 nm) ranged from 15% to 57%. Std. N95 mask performance was used as a control to compare the results with cloth masks, and our results suggest that cloth masks are only marginally beneficial in protecting individuals from particles <2.5 μm. Compared with cloth masks, disposable surgical masks are more effective in reducing particulate exposure.
- 48Wolfel, R.; Corman, V. M.; Guggemos, W.; Seilmaier, M.; Zange, S.; Muller, M. A.; Niemeyer, D.; Jones, T. C.; Vollmar, P.; Rothe, C. Virological assessment of hospitalized patients with COVID-2019. Nature 2020, 581, 465– 469, DOI: 10.1038/s41586-020-2196-x[Crossref], [PubMed], [CAS], Google Scholar48https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BB383pvVSjtQ%253D%253D&md5=c07f8994b50fb04df3fa21473c1be494Virological assessment of hospitalized patients with COVID-2019Wolfel Roman; Zange Sabine; Vollmar Patrick; Ehmann Rosina; Zwirglmaier Katrin; Corman Victor M; Muller Marcel A; Niemeyer Daniela; Jones Terry C; Bleicker Tobias; Brunink Sebastian; Schneider Julia; Drosten Christian; Guggemos Wolfgang; Seilmaier Michael; Wendtner Clemens; Jones Terry C; Rothe Camilla; Hoelscher MichaelNature (2020), 581 (7809), 465-469 ISSN:.Coronavirus disease 2019 (COVID-19) is an acute infection of the respiratory tract that emerged in late 2019(1,2). Initial outbreaks in China involved 13.8% of cases with severe courses, and 6.1% of cases with critical courses(3). This severe presentation may result from the virus using a virus receptor that is expressed predominantly in the lung(2,4); the same receptor tropism is thought to have determined the pathogenicity-but also aided in the control-of severe acute respiratory syndrome (SARS) in 2003(5). However, there are reports of cases of COVID-19 in which the patient shows mild upper respiratory tract symptoms, which suggests the potential for pre- or oligosymptomatic transmission(6-8). There is an urgent need for information on virus replication, immunity and infectivity in specific sites of the body. Here we report a detailed virological analysis of nine cases of COVID-19 that provides proof of active virus replication in tissues of the upper respiratory tract. Pharyngeal virus shedding was very high during the first week of symptoms, with a peak at 7.11 × 10(8) RNA copies per throat swab on day 4. Infectious virus was readily isolated from samples derived from the throat or lung, but not from stool samples-in spite of high concentrations of virus RNA. Blood and urine samples never yielded virus. Active replication in the throat was confirmed by the presence of viral replicative RNA intermediates in the throat samples. We consistently detected sequence-distinct virus populations in throat and lung samples from one patient, proving independent replication. The shedding of viral RNA from sputum outlasted the end of symptoms. Seroconversion occurred after 7 days in 50% of patients (and by day 14 in all patients), but was not followed by a rapid decline in viral load. COVID-19 can present as a mild illness of the upper respiratory tract. The confirmation of active virus replication in the upper respiratory tract has implications for the containment of COVID-19.
- 49Bar-On, Y. M.; Flamholz, A.; Phillips, R.; Milo, R. Science Forum: SARS-CoV-2 (COVID-19) by the numbers. eLife 2020, 9, e57309 DOI: 10.7554/eLife.57309
- 50Xing, Y.-F.; Xu, Y.-H.; Shi, M.-H.; Lian, Y.-X. The Impact of PM2. 5 on the Human Respiratory System. J. Thorac. Dis. 2016, 8 (1), E69 DOI: 10.3978/j.issn.2072-1439.2016.01.19
- 51Asadi, S.; Wexler, A. S.; Cappa, C. D.; Barreda, S.; Bouvier, N. M.; Ristenpart, W. D. Aerosol emission and superemission during human speech increase with voice loudness. Sci. Rep. 2019, 9 (1), 1– 10, DOI: 10.1038/s41598-019-38808-z[Crossref], [PubMed], [CAS], Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitVKrsrvL&md5=d1e10ff6dc9dbd100c2212be66338c0aThermo-mechanical contact problems and elastic behaviour of single and double sides functionally graded brake disks with temperature-dependent material propertiesBayat, Mehdi; Alarifi, Ibrahim M.; Khalili, Ali Akbar; El-Bagory, Tarek M. A. A.; Nguyen, Hoang Minh; Asadi, AminScientific Reports (2019), 9 (1), 1-16CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)A thermo-elastic contact problem of functionally graded materials (FGMs) rotating brake disk with different pure brake pad areas under temp. dependent material properties is solved by Finite Element Method (FEM). The properties of brake disk change gradually from metal to ceramic by power-law distribution along the radial direction from the inner to the outer surface. Areas of the pure pad are changing while the vertical force is const. The ratio of brake pad thickness to FGMs brake disk thickness is assumed 0.66. Two sources of thermal loads are considered: (1) Heat generation between the pad and brake disk due to contact friction, and (2) External thermal load due to a const. temp. at inner and outer surfaces. Mech. responses of FGMs disk are compared with several pad contact areas. The results for temp.-dependent and temp.-independent material properties are investigated and presented. The results show that the abs. value of the shear stress in temp.-dependent material can be greater than that for temp.-independent material. The radial stress for some specific grading index (n = 1.5) is compressive near the inner surface for double contact while it is tensile for a single contact. It is concluded that the radial strain for some specific value of grading index (n = 1) is lower than other FGMs and pure double side contact brake disks.
- 52Cedeño-Laurent, J. G.; Williams, A.; MacNaughton, P.; Cao, X.; Eitland, E.; Spengler, J.; Allen, J. Building Evidence for Health: Green Buildings, Current Science, and Future Challenges. Annu. Rev. Public Health 2018, 39 (1), 291– 308, DOI: 10.1146/annurev-publhealth-031816-044420[Crossref], [PubMed], [CAS], Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1Mvgt1ajug%253D%253D&md5=f9f4460df6f0e48e922131cf25c5db72Building Evidence for Health: Green Buildings, Current Science, and Future ChallengesCedeno-Laurent J G; Williams A; MacNaughton P; Cao X; Eitland E; Spengler J; Allen JAnnual review of public health (2018), 39 (), 291-308 ISSN:.Civilizational challenges have questioned the status quo of energy and material consumption by humans. From the built environment perspective, a response to these challenges was the creation of green buildings. Although the revolutionary capacity of the green building movement has elevated the expectations of new commercial construction, its rate of implementation has secluded the majority of the population from its benefits. Beyond reductions in energy usage and increases in market value, the main strength of green buildings may be the procurement of healthier building environments. Further pursuing the right to healthy indoor environments could help the green building movement to attain its full potential as a transformational public health tool. On the basis of 40 years of research on indoor environmental quality, we present a summary of nine environment elements that are foundational to human health. We posit the role of green buildings as a critical research platform within a novel sustainability framework based on social-environmental capital assets.
- 53Li, Y.; Leung, G. M.; Tang, J. W.; Yang, X.; Chao, C. Y.; Lin, J. Z.; Lu, J. W.; Nielsen, P. V.; Niu, J.; Qian, H. Role of Ventilation in Airborne Transmission of Infectious Agents in the Built Environment-a Multidisciplinary Systematic Review. Indoor Air 2007, 17 (1), 2– 18, DOI: 10.1111/j.1600-0668.2006.00445.x[Crossref], [PubMed], [CAS], Google Scholar53https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD2s%252FlsVajtw%253D%253D&md5=5b3cf1b64261320f3f32226ba12a161bRole of ventilation in airborne transmission of infectious agents in the built environment - a multidisciplinary systematic reviewLi Y; Leung G M; Tang J W; Yang X; Chao C Y H; Lin J Z; Lu J W; Nielsen P V; Niu J; Qian H; Sleigh A C; Su H-J J; Sundell J; Wong T W; Yuen P LIndoor air (2007), 17 (1), 2-18 ISSN:0905-6947.There have been few recent studies demonstrating a definitive association between the transmission of airborne infections and the ventilation of buildings. The severe acute respiratory syndrome (SARS) epidemic in 2003 and current concerns about the risk of an avian influenza (H5N1) pandemic, have made a review of this area timely. We searched the major literature databases between 1960 and 2005, and then screened titles and abstracts, and finally selected 40 original studies based on a set of criteria. We established a review panel comprising medical and engineering experts in the fields of microbiology, medicine, epidemiology, indoor air quality, building ventilation, etc. Most panel members had experience with research into the 2003 SARS epidemic. The panel systematically assessed 40 original studies through both individual assessment and a 2-day face-to-face consensus meeting. Ten of 40 studies reviewed were considered to be conclusive with regard to the association between building ventilation and the transmission of airborne infection. There is strong and sufficient evidence to demonstrate the association between ventilation, air movements in buildings and the transmission/spread of infectious diseases such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS. There is insufficient data to specify and quantify the minimum ventilation requirements in hospitals, schools, offices, homes and isolation rooms in relation to spread of infectious diseases via the airborne route. PRACTICAL IMPLICATION: The strong and sufficient evidence of the association between ventilation, the control of airflow direction in buildings, and the transmission and spread of infectious diseases supports the use of negatively pressurized isolation rooms for patients with these diseases in hospitals, in addition to the use of other engineering control methods. However, the lack of sufficient data on the specification and quantification of the minimum ventilation requirements in hospitals, schools and offices in relation to the spread of airborne infectious diseases, suggest the existence of a knowledge gap. Our study reveals a strong need for a multidisciplinary study in investigating disease outbreaks, and the impact of indoor air environments on the spread of airborne infectious diseases.
- 54Ai, Z. T.; Huang, T.; Melikov, A. K. Airborne Transmission of Exhaled Droplet Nuclei between Occupants in a Room with Horizontal Air Distribution. Build. Environ. 2019, 163, 106328, DOI: 10.1016/j.buildenv.2019.106328
- 55Li, Y.; Nielsen, P. V. CFD and ventilation research. Indoor Air 2011, 21 (6), 442– 453, DOI: 10.1111/j.1600-0668.2011.00723.x[Crossref], [PubMed], [CAS], Google Scholar55https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3MbjsFWktQ%253D%253D&md5=f240d6e1a739c5c0b882e27f2997b915CFD and ventilation researchLi Y; Nielsen P VIndoor air (2011), 21 (6), 442-53 ISSN:.UNLABELLED: There has been a rapid growth of scientific literature on the application of computational fluid dynamics (CFD) in the research of ventilation and indoor air science. With a 1000-10,000 times increase in computer hardware capability in the past 20 years, CFD has become an integral part of scientific research and engineering development of complex air distribution and ventilation systems in buildings. This review discusses the major and specific challenges of CFD in terms of turbulence modelling, numerical approximation, and boundary conditions relevant to building ventilation. We emphasize the growing need for CFD verification and validation, suggest ongoing needs for analytical and experimental methods to support the numerical solutions, and discuss the growing capacity of CFD in opening up new research areas. We suggest that CFD has not become a replacement for experiment and theoretical analysis in ventilation research, rather it has become an increasingly important partner. PRACTICAL IMPLICATIONS: We believe that an effective scientific approach for ventilation studies is still to combine experiments, theory, and CFD. We argue that CFD verification and validation are becoming more crucial than ever as more complex ventilation problems are solved. It is anticipated that ventilation problems at the city scale will be tackled by CFD in the next 10 years.
- 56Ramponi, R.; Blocken, B. CFD simulation of cross-ventilation for a generic isolated building: impact of computational parameters. Build. Sci. 2012, 53, 34– 48, DOI: 10.1016/j.buildenv.2012.01.004
- 57Owen, M. S. ASHRAE Handbook: HVAC Systems and Equipment; American Society of Heating, Refrigerating and Air-Conditioning Engineers: Atlanta, 2004.Google ScholarThere is no corresponding record for this reference.
- 58Weather Averages for the United States.https://www.currentresults.com/Weather/US/weather-averages-index.php (accessed 2020-05-07).Google ScholarThere is no corresponding record for this reference.
- 59Liao, L.; Xiao, W.; Zhao, M.; Yu, X.; Wang, H.; Wang, Q.; Chu, S.; Cui, Y. Can N95 Respirators Be Reused after Disinfection? How Many Times?. ACS Nano 2020, 14 (5), 6348– 6356, DOI: 10.1021/acsnano.0c03597[ACS Full Text], [CAS], Google Scholar59https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXosVCmt7o%253D&md5=5fc1b3a9b67826faa66784801f5cf1d8Can N95 Respirators Be Reused after Disinfection? How Many Times?Liao, Lei; Xiao, Wang; Zhao, Mervin; Yu, Xuanze; Wang, Haotian; Wang, Qiqi; Chu, Steven; Cui, YiACS Nano (2020), 14 (5), 6348-6356CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The coronavirus disease 2019 (COVID-19) pandemic has led to a major shortage of N95 respirators, which are essential for protecting healthcare professionals and the general public who may come into contact with the virus. Thus, it is essential to det. how we can reuse respirators and other personal protective equipment in these urgent times. We investigated multiple commonly used disinfection schemes on media with particle filtration efficiency of 95%. Heating was recently found to inactivate the virus in soln. within 5 min at 70°C and is among the most scalable, user-friendly methods for viral disinfection. We found that heat (≤85°C) under various humidities (≤100% relative humidity, RH) was the most promising, nondestructive method for the preservation of filtration properties in meltblown fabrics as well as N95-grade respirators. At 85°C, 30% RH, we were able to perform 50 cycles of heat treatment without significant changes in the filtration efficiency. At low humidity or dry conditions, temps. up to 100°C were not found to alter the filtration efficiency significantly within 20 cycles of treatment. UV irradn. was a secondary choice, which was able to withstand 10 cycles of treatment and showed small degrdn. by 20 cycles. However, UV can potentially impact the material strength and subsequent sealing of respirators. Finally, treatments involving liqs. and vapors require caution, as steam, alc., and household bleach all may lead to degrdn. of the filtration efficiency, leaving the user vulnerable to the viral aerosols.
- 60Zhao, M.; Liao, L.; Xiao, W.; Yu, X.; Wang, H.; Wang, Q.; Lin, Y. L.; Kilinc-Balci, F. S.; Price, A.; Chu, L.; Chu, M. C.; Chu, S.; Cui, Y. Household materials selection for homemade cloth face coverings and their filtration efficiency enhancement with triboelectric charging. Nano Lett. 2020, 20 (7), 5544– 5552, DOI: 10.1021/acs.nanolett.0c02211[ACS Full Text], [CAS], Google Scholar60https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhtVOmtLbJ&md5=27921343d002cc18bed5f34b01f0c29fHousehold Materials Selection for Homemade Cloth Face Coverings and Their Filtration Efficiency Enhancement with Triboelectric ChargingZhao, Mervin; Liao, Lei; Xiao, Wang; Yu, Xuanze; Wang, Haotian; Wang, Qiqi; Lin, Ying Ling; Kilinc-Balci, F. Selcen; Price, Amy; Chu, Larry; Chu, May C.; Chu, Steven; Cui, YiNano Letters (2020), 20 (7), 5544-5552CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)The COVID-19 pandemic is currently causing a severe disruption and shortage in the global supply chain of necessary personal protective equipment (e.g., N95 respirators). The U.S. CDC has recommended use of household cloth by the general public to make cloth face coverings as a method of source control. We evaluated the filtration properties of natural and synthetic materials using a modified procedure for N95 respirator approval. Common fabrics of cotton, polyester, nylon, and silk had filtration efficiency of 5-25%, polypropylene spunbond had filtration efficiency 6-10%, and paper-based products had filtration efficiency of 10-20%. An advantage of polypropylene spunbond is that it can be simply triboelec. charged to enhance the filtration efficiency (from 6 to >10%) without any increase in pressure (stable overnight and in humid environments). Using the filtration quality factor, fabric microstructure, and charging ability, we are able to provide an assessment of suggested fabric materials for homemade facial coverings.
- 61Konda, A.; Prakash, A.; Moss, G. A.; Schmoldt, M.; Grant, G. D.; Guha, S. Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS Nano 2020, 14 (5), 6339– 6347, DOI: 10.1021/acsnano.0c03252[ACS Full Text], [CAS], Google Scholar61https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXnslChsr4%253D&md5=961b798525395cbb0bc53e325418e39dAerosol Filtration Efficiency of Common Fabrics Used in Respiratory Cloth MasksKonda, Abhiteja; Prakash, Abhinav; Moss, Gregory A.; Schmoldt, Michael; Grant, Gregory D.; Guha, SupratikACS Nano (2020), 14 (5), 6339-6347CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The emergence of a pandemic affecting the respiratory system can result in a significant demand for face masks. This includes the use of cloth masks by large sections of the public, as can be seen during the current global spread of COVID-19. However, there is limited knowledge available on the performance of various commonly available fabrics used in cloth masks. Importantly, there is a need to evaluate filtration efficiencies as a function of aerosol particulate sizes in the 10 nm to 10μm range, which is particularly relevant for respiratory virus transmission. We have carried out these studies for several common fabrics including cotton, silk, chiffon, flannel, various synthetics, and their combinations. Although the filtration efficiencies for various fabrics when a single layer was used ranged from 5 to 80% and 5 to 95% for particle sizes of <300 nm and >300 nm, resp., the efficiencies improved when multiple layers were used and when using a specific combination of different fabrics. Filtration efficiencies of the hybrids (such as cotton-silk, cotton-chiffon, cotton-flannel) was >80% (for particles <300 nm) and >90% (for particles >300 nm). We speculate that the enhanced performance of the hybrids is likely due to the combined effect of mech. and electrostatic-based filtration. Cotton, the most widely used material for cloth masks performs better at higher weave densities (i.e., thread count) and can make a significant difference in filtration efficiencies. Our studies also imply that gaps (as caused by an improper fit of the mask) can result in over a 60% decrease in the filtration efficiency, implying the need for future cloth mask design studies to take into account issues of "fit" and leakage, while allowing the exhaled air to vent efficiently. Overall, we find that combinations of various commonly available fabrics used in cloth masks can potentially provide significant protection against the transmission of aerosol particles.
Supporting Information
ARTICLE SECTIONSThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03331.
Detailed information about the modeling framework, analysis on the Brownian motion, size distribution and evaporation dynamics of respiratory droplets, distance-dependent viral load distribution, and calculation of suspending aerosol particles (PDF)
Terms & Conditions
Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.