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Can N95 Respirators Be Reused after Disinfection? How Many Times?

  • Lei Liao
    Lei Liao
    4C Air, Inc., Sunnyvale, California 94089, United States
    More by Lei Liao
  • , 
  • Wang Xiao
    Wang Xiao
    4C Air, Inc., Sunnyvale, California 94089, United States
    More by Wang Xiao
  • , 
  • Mervin Zhao
    Mervin Zhao
    4C Air, Inc., Sunnyvale, California 94089, United States
    More by Mervin Zhao
    Orcidhttp://orcid.org/0000-0002-7313-7150
  • , 
  • Xuanze Yu
    Xuanze Yu
    4C Air, Inc., Sunnyvale, California 94089, United States
    More by Xuanze Yu
  • , 
  • Haotian Wang
    Haotian Wang
    4C Air, Inc., Sunnyvale, California 94089, United States
    More by Haotian Wang
  • , 
  • Qiqi Wang
    Qiqi Wang
    4C Air, Inc., Sunnyvale, California 94089, United States
    More by Qiqi Wang
  • , 
  • Steven Chu
    Steven Chu
    Department of Physics, Stanford University, Stanford, California 94305, United States
    Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, United States
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  • , and 
  • Yi Cui*
    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
    *Email: [email protected]
    More by Yi Cui
    Orcidhttp://orcid.org/0000-0002-6103-6352
Cite this: ACS Nano 2020, 14, 5, 6348–6356
Publication Date (Web):May 5, 2020
https://doi.org/10.1021/acsnano.0c03597
Copyright © 2020 American Chemical Society
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Abstract

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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 determine 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 solution 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, temperatures up to 100 °C were not found to alter the filtration efficiency significantly within 20 cycles of treatment. Ultraviolet (UV) irradiation was a secondary choice, which was able to withstand 10 cycles of treatment and showed small degradation by 20 cycles. However, UV can potentially impact the material strength and subsequent sealing of respirators. Finally, treatments involving liquids and vapors require caution, as steam, alcohol, and household bleach all may lead to degradation of the filtration efficiency, leaving the user vulnerable to the viral aerosols.

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  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 pandemic with over three million confirmed cases and new cases increasing by ∼10% per day (at the time of writing) (1) that has caused major disruptions to nearly all facets of everyday life around the world. The disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was first detected in Wuhan, China. (2,3) The virus is likely of zoonotic origin and, like the SARS-CoV, enters human cells via the angiotensin-converting enzyme 2 (ACE2). ACE2 is a membrane protein that is responsible for regulating vasoconstriction and blood pressure and serves as an entry point for coronaviruses found in the lungs, heart, kidneys, and intestines. SARS-CoV-2 utilizes ACE2 more efficiently than does SARS-CoV, which may explain why the human-to-human transmissibility of COVID-19 is so high. (4)
Once infected, the patient exhibits flu-like symptoms such as fever, chest tightness, dry cough, and, in some cases, severe pneumonia and acute respiratory distress syndrome (ARDS) develops. (5−8) Because the incubation period is ca. 3–4 days but can be as long as 20 days, along with the presence of asymptomatic carriers, the virus has been extremely difficult to contain. (9) Although the initial mortality rate was estimated to be ca. 3.5% in China, compounding the longer incubation period and testing delays has led to new global estimates of ca. 5.7%. (10)
Although the precise mode SARS-CoV-2’s viral transmission is not known, a primary transmission mode in viruses such as SARS and influenza is through short-range aerosols and droplets. (11) When a person infected with a virus breathes, speaks, sings, coughs, or sneezes, micron-sized aerosols containing the virus are released into the air. Data gathered from influenza patients suggest that these aerosols are typically fine (<5 μm) or coarse (>5 μm). (11−13) Coarse particles can settle due to gravity within 1 h. Fine particles, however, especially those smaller than 1 μm, can essentially stay in the air nearly indefinitely. Droplets, or particles >10 μm, settle rapidly and are not typically deposited in the respiratory tract through means of aerosol inhalation. Particles larger than 5 μm typically only reach the upper respiratory tract, whereas fine particles <5 μm are critically able to reach the lower respiratory tract, similar to harmful particulate matter pollution (Figure 1). Although coughing and sneezing provide many aerosols, the size distribution and number of particles emitted during normal speech serve as a significant viral transmitter. (12) Singing has been found to be comparable to continuous coughing in the transmission of airborne pathogens, (14) which was demonstrated during a choir practice on March 10, 2020 in Washington state. Although the choir members did not touch each other or share music during the rehearsal, 45 out of the 60 members of the Skagit Valley Choir were diagnosed with the virus 3 weeks later, and two had died.

Figure 1

Figure 1. Transmission of SARS-CoV-2 through viral aerosols. Image of SARS-CoV-2 courtesy of the CDC.

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For dangerous airborne particulates, including viral aerosols during the current COVID-19 pandemic, the United States Centers for Disease Control and Prevention (CDC) recommends the usage of N95 filtering facepiece respirators (FFR) as personal protective equipment for healthcare professionals. (15−17) The N95 grade is determined by the CDC’s National Institute of Occupational Safety and Health (NIOSH) (document 42 CFR Part 84), which designates a minimum filtration efficiency of 95% for 0.3 μm (aerodynamic mass mean diameter) of sodium chloride aerosols. In addition to N95, there are N99 and N100 standards, which correspond to filtration efficiencies of 99% and 99.97%, respectively. For oil-based aerosols (DOP), NIOSH also has created grades R and P (with filtration efficiencies 95–99.97%). Elsewhere around the globe, the equivalent filtration grades to N95 are FFP2 (European Union), KN95 (China), DS/DL2 (Japan), and KF94 (South Korea). Although the actual SARS-CoV-2 virus is ca. 150 nm, (18) commonly found N95 respirators can offer protection against particles as small as 80 nm with 95% filtration efficiency (initial testing, not loaded). (19) With the actual viral aerosols in the ∼1 μm range, the N95 FFRs’ filtration efficiency should be sufficient for personal protection.
The N95 FFR is composed of multiple layers of, typically, polypropylene nonwoven fabrics (Figure 2A). (20) Among these layers, the most critical is that which is produced by the meltblown process. In typical FFRs, the meltblown layer is 100–1000 μm in thickness and composed of polypropylene microfibers with diameters in the range of ∼1–10 μm, as seen in the scanning electron microscope (SEM) images in Figure 2B,C. Due to the production method, meltblown fibers produce a lofty nonwoven material where the fibers can stack and create a three-dimensional network that has a porosity of 90%, (21) leading to high air permeability.

Figure 2

Figure 2. Meltblown fabrics in N95 FFRs. (A) Peeling apart a representative N95 FFR reveals multiple layers of nonwoven materials. (B) Scanning electron microscope (SEM) cross-section image reveals the middle meltblown layer has thinner fibers with thickness around 300 μm. (C) SEM image of meltblown fibers reveals a complicated randomly oriented network of fibers, with diameters in the range of ∼1–10 μm. (D) Schematic illustration of meltblown fibers (left) without and (right) with electret charging. In the left figure, smaller particles are able to pass through to the user, but particles are electrostatically captured in the case of an electret (right).

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However, given that the fiber diameters are relatively small and the filters’ void space is large, the filtration efficiencies of meltblown fabrics by themselves should not be adequate for fine particle filtration (Figure 2D). To improve the filtration efficiency while keeping the same high air permeability, these fibers are charged through corona discharge and/or triboelectric means into quasi-permanent dipoles called electrets. (22,23) Once they are charged, the filter can significantly increase its filtration efficiency without adding any mass or density to the structure. In addition, whereas other filter media may decrease in efficiency when loading the filter with more aerosol (NaCl, DOP), the meltblown electrets are able to keep a relatively consistent efficiency throughout the test. (24)
The COVID-19 pandemic has led to a significant shortage of N95 FFRs, (25) especially among healthcare providers. Although the virus will eventually become inactive on the mask surface and it is unlikely to penetrate fully to the user’s intake side, a recent study shows that 72 h were required for the concentration of SARS-CoV-1 and SARS-CoV-2 viruses on plastic surfaces (40% RH and 21–23 °C) to be reduced by 3 orders of magnitude (from 103.7 to 100.6 TCID50 per mL of medium). (26) Assuming a similar longevity on FFR surfaces, it is important to develop procedures for the safe and frequent reuse of FFRs without reducing the filtration efficiency. The CDC has recommended many disinfection or sterilization methods, typically involving chemical, radiative, or temperature treatments. (27) In brief, the mechanisms of disinfection or sterilization of bacteria and viruses include protein denaturation (alcohols, heat), DNA/RNA disruption (UV, peroxides, oxidizers), and cellular disruption (phenolics, chlorides, aldehydes). Although none of these methods have been extensively evaluated for SARS-CoV-2 inactivation specifically, we tested methods that can be easily deployed within a hospital setting, and possibly accessible for the general population, with relatively high throughput for FFR reuse.

Results

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Among the CDC forms of disinfection, we chose five commonly used and potentially scalable, user-friendly methods: (1) heat under various humidities (heat denaturation inactivates SARS-CoV with temperatures >65 °C in solution, and possibly SARS-CoV-2 with temperatures >70 °C for 5 min); (28−30) (2) steam (100 °C heat-based denature); (3) 75% alcohol (denaturing of the virus, based on the CDC); (4) household diluted chlorine-based solution (oxidative or chemical damage, based on the CDC); and (5) ultraviolet germicidal irradiation (UVGI was able to inactivate the SARS-CoV in solution with UV–C light at a fluence of ∼3.6 J/cm2). (28) An oven, a UV–C sterilizer cabinet (found in barbershops or salons), steam, or liquid sprays can all realistically be deployed in the modern hospital setting and potentially in homes if needed. We did not consider some other common but more inaccessible techniques (equipment such as electron beam irradiation or plasma generators can be expensive or dangerous) or techniques known to cause damage to the FFR. (31)
Due to the shortage of FFRs, data collected were tested on a meltblown fabric (20 g/m2) with initial efficiency ≥95% (full details are listed in the Methods), unless otherwise specified. These samples are representative of how the filtration efficiency in a N95 FFR may change given exposure to these treatments in the worst-case scenario (i.e., no protective layer of the FFR). All meltblown samples were characterized using an industry standard Automated Filter Tester 8130A (TSI, Inc.) with a flow rate of 32 L/min and NaCl aerosol (0.26 μm mass median diameter). We subjected the meltblown samples to the aforementioned five disinfection methods and summarized the data in Table 1.
Table 1. One-Time Disinfection Treatment on a Meltblown Fabrica
treatmentmode of applicationtreatment time (min)filtration efficiency (%)pressure drop (Pa)
initial samples  96.52 ± 1.378.7 ± 1.0
dry heat (75 °C)static-air oven3096.67 ± 0.656.0 ± 1.0
steambeaker of boiling water1095.16 ± 0.739.0 ± 1.0
ethanol (75%)immersion and air dryuntil dry56.33 ± 3.037.7 ± 0.6
chlorine-based (2%)light spray and air dry573.11 ± 7.329.0 ± 1.0
UVGI (254 nm, 8 W)sterilization cabinet3095.50 ± 1.597.0 ± 0.0
a

The data from the initial samples displayed here are used throughout the remainder of the text and represent the mean and standard deviation from 30 samples. For all other data here, three samples were used for each initial treatment.

From the first disinfection, we can clearly note that the solution-based methods (ethanol and chlorine-based solution) drastically degraded the filtration efficiency to unacceptable levels, while the pressure drop remained comparable. As the pressure drop remained constant, this indicated that the loftiness and structure of the meltblown were unchanged, and the resultant efficiency degradation is the result of less apparent static charge on the electret (Figure S1). It is hypothesized in the literature that small molecules such as solvents can adsorb onto the fabrics’ fibers and either screen or possibly lift the frozen charges of the electret, (32) which would decrease the filtration efficiency. In the case of disinfection with ethanol-based solutions, recent preliminary work also shows that vacuum drying may be able to restore the efficiency of FFRs. (33) It is also possible that the chlorine-based solution may degrade the efficiency less than the alcohol-based solution due to the higher water content. As polypropylene is hydrophobic, the chlorine-based solution may have a more difficult time penetrating the fabric and the static charge of fibers deeper within the meltblown may be less affected.
These initial results are mostly in agreement with a NIOSH-published report regarding the decontamination of whole FFRs, (34) though it placed more focus on gas-based methods, which could be suitable to well-controlled industrial-scale disinfection. However, this may not be practical for on-site disinfection within the current hospital and clinic infrastructure. The report found that bleach (immersion in a diluted solution) resulted in less of a drop in efficiency than our results indicated, but the authors noted that there were strong odors from off-gassing, which is another reason to exclude this as a method to consider for the end-user.
We chose to focus on the three remaining treatment methods to perform multiple treatment cycles. The meltblown fabrics after 10 cycles of each treatment are summarized in Figure 3 (data provided in Table S1). After three treatments of these three methods, the meltblown fabric still has characteristics similar to the initial sample. However, after five steam treatments, the efficiency has a sharp drop which continues at cycle 10 (Table S2). Similar to the alcohol- and chlorine-solution treatments, the pressure drop can be maintained at ∼8–9 Pa, but the efficiency degrades to around ∼80%, which would be concerning in an environment with high viral aerosol concentrations. As with the solution treatments, the pressure drops remained similar, which suggests it is also due to the decay of static charge. The dwelling time and frequency may be critical for how well the static charge can be preserved. If steam treatments saturate the fibers many times and condense water droplets on the fibers, it is possible that the static charge decays after multiple treatments. Because this decay is due to the direct water molecule contact with the fibers, it may be possible to alleviate the static decay if the fibers do not come into contact with the vapor directly (sealed container, apparatus, bag, etc.) and steam only serves as the heating element.

Figure 3

Figure 3. The 10 treatment cycle evolution of filtration characteristics. (A) Efficiency evolution where it is clear that steam treatment results in a degradation of efficiency. (B) Pressure drop evolution where it is not apparent that any structure or morphology change has occurred in the meltblown fabrics.

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Given that steam also resulted in eventual efficiency degradation, we further determined the limits of temperature and humidity. We performed multiple humidity experiments (30%, 70%, and 100% RH) at 85 °C (20 min/cycle) and observed no appreciable degradation of efficiency at any humidity level (Figure 4A,B). At 85 °C, 30% RH, we observed no efficiency degradation over 50 cycles on a meltblown fabric (Figure 4C,D). Using less harsh conditions (75 °C, dry heat), the results are expectedly in agreement (Figure S2). These results are further confirmed when testing multiple N95-level FFRs from various countries (listed in Methods) at 85 °C, 30% and 100% RH for 20 cycles (Figure 4E,F). Testing conditions for the FFRs were under a flow rate of 85 L/min. From all the FFRs, we observed little change in the filtration properties, as all FFRs with filtration efficiency >95% were able to retain filtration efficiencies >95% after 20 cycles of heat treatment, even in a humid environment.

Figure 4

Figure 4. Temperature and humidity evolution of meltblown and FFR filtration characteristics. (A, B) Evolution of meltblown fabrics’ filtration characteristics at 85 °C under different humidities, efficiency (A) and pressure drop (B). (C, D) Evolution of filtration characteristics on a meltblown fabric under 85 °C, 30% RH, efficiency (C) and pressure drop (D). (E, F) Evolution of the filtration characteristics on an N95-level FFRs with 85 °C, under 30% and 100% RH (measured at a flow rate of 85 L/min), efficiency (E) and pressure drop (F). The left-to-right of all FFR brands is as follows: (1) initial (leftmost, solid pattern, tested in ambient conditions), (2) 85 °C, 30% RH 10 cycles, (3) 85 °C, 30% RH 20 cycles, (4) 85 °C, 100% RH 10 cycles, and (5) 85 °C, 100% RH 20 cycles. (G, H) Temperature dependence of meltblown fabrics’ filtration characteristics over 20 cycles with RH < 30%, efficiency (G) and pressure drop (H).

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To determine the upper limit of applicable temperature, we tested low humidity conditions (≤30% RH) up to 125 °C (10 min/cycle), plotted in Figure 4G,H (data provided in Table S3), as higher temperatures should lead to a shorter minimum treatment time and an increase in the method turnover speed. There is little to no change in the filtration efficiency and pressure drop up to 100 °C in low-moisture conditions. However, at 125 °C, there is a sharp drop in the filtration efficiency while maintaining a constant pressure drop at around cycle 5. Similarly, the lack of pressure drop change indicates that the degradation is also due to the static decay. Considering the higher temperature, polypropylene’s melting point (130–170 °C), as well as the thin and fibrous nature of the media, it is possible that the higher temperature is enough to relax the microscopic charge state within the polymer, resulting in some of the quasi-stable polarization to become depolarized to their neutral state. From SEM images, we did not identify any morphological changes and did not observe any apparent physical deformations (Figure S3), which may support this conclusion. This effect is not as strong as direct solvent contact, which reduced the filtration efficiency to <80%, whereas 125 °C reduced the efficiency to ∼90%. The mechanism of efficiency degradation may differ, as the solvent may form molecular adsorption layers or possibly liberate charge traps, but higher temperatures provide energy to return some of the fibers’ polarized state to a relaxed state.
Heat was a promising scalable method that may be suitable for FFR reuse. We can conclude that the highest subjectable temperature to the FFR for repeated use with ≥95% efficiency is <100 °C. At temperatures of ≤85 °C, humidity does not seem to play a crucial role in the filtration properties, as FFRs tested at a near 100% RH at 85 °C were unaffected. However, as steam results in a decrease in efficiency, the humidity should be kept low if approaching 100 °C. The temperature range here may pose some limitations in the available equipment, but we believe the current hospital infrastructure, and possibly the general population, should be able to perform these treatments. This includes using dryers, ovens, circulators, or even hot air guns, all of which are relatively scalable and user-friendly. Although the most common method to inactivate SARS-CoV-2 in solution is 56 °C for 30 min in a laboratory setting, (35) repeated treatments at temperatures below 65 °C (30 min) is not advised, as it was the reported temperature required to inactivate SARS-CoV in solution and limit it to undetectable traces. (29) Because these prior inactivation tests occurred in solution, further study on the heat inactivation of aerosolized viruses is required.
It is important to note that the real-world use of FFRs may lead to contamination of the nonwoven layers with sweat and/or oral droplets (dirt, salts, or other chemicals/particles), which may negatively impact the efficiency (adsorption, charge degradation, or even physical damage after prolonged periods). If these contaminants impact the electrostatic ability of the respirator, the heat treatment would not be able to restore this charge and would, at best, keep the efficiency as is. Further work may be needed to test the degradation of efficiency after use and if such heating procedures on used FFRs are changed by the introduction of these usage-incurred contaminants.
Finally, we tested the effect of UVGI on meltblown samples up to 20 cycles (Figure 5). The UVGI sterilization cabinet here provides UV–C light centered at a wavelength of 254 nm with an intensity of 8 W. The UV–C light areal intensity distribution is not uniform inside the cabinet, and its exact value needs to be measured in the future for dose determination, as the necessary radiation to inactivate SARS-CoV was previously found to be above ∼3.6 J/cm2. (28) At 10 cycles, the data are in agreement with the NIOSH report, (34) but efficiency eventually decays to 93% at 20 cycles, making it unsuitable for N95-grade FFRs by itself.

Figure 5

Figure 5. Effect of UVGI on meltblown filtration characteristics. (A) Efficiency of meltblown fabric that slightly changes after 10 cycles of UVGI. (B) Pressure drop after UVGI treatments remains similar. The larger error bar in the initial data is due to the meltblown fabric originating from various locations on the roll, whereas the meltblown fabrics used in the treatment originated from a similar location on the roll.

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Although UV radiation may possess enough energy to break the chemical bonds and degrade polypropylene, the dosage of the sterilization chamber is relatively low, and the material degrades slowly. This finding is supported by previous experiments that showed UV–C doses up to 950 J/cm2 did not appreciably change the filtration efficiency. (36) A possible concern regarding UVGI disinfection for FFRs relates to the UV penetration depth. Because UV–C has a wavelength around 250 nm and polypropylene is a UV absorber, it is difficult to conclude if smaller viral particles deep within the filter can be deactivated through UVGI. If the particles are of a larger size and remain localized on the surface, UVGI may be a candidate for FFR reuse. Furthermore, this means that UVGI requires FFRs not to be stacked, as the incident radiation will only be absorbed by the topmost surface. Another disadvantage is that UVGI was reported to significantly impact the mechanical strength of some FFRs with doses of around 1000 J/cm2. (36)
Therefore, UVGI may be a useful disinfection technique, but the exact exposure or intensity of the UV–C light fluence on the mask surface would need to be verified. The variation in UVGI intensity has been the cause of discrepancies in the literature, as 3M’s own internal reports recently showed that their UVGI treatments damaged particular FFRs, (37) whereas other reports show that UVGI cycling on multiple N95 FFRs had minimal or no impact. (31)
Most of our tests were performed on meltblown fabrics with an initial efficiency of >95% due to the current shortage of FFRs, leaving concern over whether other FFR components (straps, valves, nosepiece, foam, etc.) can change in these treatment environments. These components can impact the fit and sealing of the FFR, which is equally important as the FFR efficiency itself. From our experiments, we also used typical N95-grade FFRs to test the strap elasticity and structural integrity after heat treatments. We noted no apparent or qualitative change in the strap elasticity or fit compared with the untreated model for the heat treatments, and quantitative studies confirmed this finding. (38) Although no qualitative damage was observed on the UV-treated FFRs, quantitative tests revealed that UVGI treatments at this dosage can lead to improper fitting. (38)
Because actually donning and using the respirator impacts the structural stability of such components, particular care needs to be taken in the interpretation of these results. Previous reports indicated that FFRs can safely be worn up to five times, but beyond five times may result in a less-than-adequate fit. (39) During this crisis, users have to make sure that the fit of the FFRs after treatment is adequate and that they are not left vulnerable due to leakage. Mask producers or users may need to consider straps that are more robust for reuse or that can withstand treatment conditions.

Conclusions

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In conclusion, COVID-19 is an extremely contagious disease that requires healthcare professionals to take caution with necessary protective equipment. The current shortage of N95 FFRs during this time of rapidly spreading infection may be mitigated by methods that will enable their safe reuse. We tested methods that may be suitable for the reuse of particulate respirators and hope our results will be useful in helping hospitals, health care facilities, and the public in formulating safe standard operating procedures so that virus inactivation is assured while not compromising mask protection. We reiterate that although these methods were not tested on FFRs that have been exposed to SARS-CoV-2, these methods use disinfection precedents set by either SARS-CoV or recent data based on inactivation of SARS-CoV-2 in solution. We found that of commonly deployable methods, heating (dry or in the presence humidity) <100 °C can preserve the filtration characteristics of a pristine N95 respirator. The UVGI (254 nm, 8 W) sterilizer cabinet used in these tests does not have enough dose to impact the filtration properties within a reasonable number of treatment cycles and may be considered for disinfection, however the exact dose output of the cabinet would need to be determined such that it is suitable for inactivation of SARS-CoV-2 with minimal FFR damage. Using steam to disinfect requires caution, as the treatments may seem to be suitable, but prolonged treatment may leave the user with unsuitable protection. Finally, we advise against liquid contact, such as alcohol solutions, chlorine-based solutions, or soaps to clean the respirator, as this will lead to a degradation in the static charge that is necessary for the FFR to meet the N95 standard.

Methods

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Sample Preparation

Meltblown fabric was procured from Guangdong Meltblown Technology Co., Ltd. under the sample name TM95 with a 20 g/m2 basis weight and initial filtration efficiency of ≥95%. All of the meltblown samples used were from this source. Each sample was cut to approximately 15 cm × 15 cm. All sample testing was performed on an Automated Filter Tester 8130A (TSI, Inc.) using a flow rate of 32 L/min and NaCl as the aerosol (0.26 μm mass median diameter). Each average measurement contains at least three individual sample measurements.
We chose disposable N95-grade FFRs for testing: 3M 8210 (NIOSH N95), 4C Air, Inc. (GB2626 KN95), ESound (GB2626 KN95), and Onnuriplan (KFDA KF94). These FFRs are referred to as “3M”, “4C”, “ES”, and “OP”, respectively, in figures. Full FFR testing used a flow rate of 85 L/min.
Scanning electron microscope images were recorded using a Phenom Pro SEM, at 10 kV.

Heat Treatment

Samples were loaded into a preheated five-sided heating chamber (Across International, LLC or SH-642, ESPEC) at the temperatures and times given in the main text. Dry heat was applied using the Across International vacuum heating oven under ambient conditions. In the case of the SH-642, the humidity was set to the lowest value (30% RH up to 85 °C; above 85 °C, the humidity is <30% but cannot be controlled). High humidity (100% RH) was simulated via sealing meltblown fabrics, or FFRs, inside a polyethylene bag with 0.3 mL of water and placing them inside the SH-642 chamber. The resting time between cycles was 10 min for the 75 and 85 °C treatments and 5 min for the 100 and 125 °C treatments. After resting, the samples were returned to the chamber to begin the next cycle. We initially chose 75 °C due to the presence of blanket warming ovens in hospital environments that can reach ∼80 °C. Further experiments used 85 °C, in the event that 75 °C is insufficient to inactivate SARS-CoV-2. Microwaving was not considered as many FFRs contain metals which may spark and melt the fabric.

Steam Treatment

Three samples were stacked on top of a beaker with boiling water inside (at around 15 cm above the water). The samples were left on top of the beaker and steamed for 10 min, and afterward they were left to air-dry completely (to touch). Samples were either tested or placed back on top of the beaker to continue the next treatment cycle.

Alcohol Treatment

Samples were immersed into a solution of 75% ethanol and left to air-dry (hanging) and subsequently tested.

Chlorine Solution Treatment

Samples were sprayed with approximately 0.3–0.5 mL of household chlorine-based disinfectant (∼2% NaClO). Samples were left to air-dry and off-gas completely,while hanging. Samples were tested.

UVGI

Samples were placed into a UV sterilizer cabinet (CHS-208A), with a 254 nm, 8 W lamp, and 475 cm2 internal area. Samples were irradiated for 30 min and left to stand under ambient conditions for 10 min per cycle. Samples were either returned to the chamber for the next cycle or tested.

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsnano.0c03597.

  • Additional SEM images, plots, and tables with compiled data (PDF)

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Author Information

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  • Corresponding Author
    • 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;  Orcidhttp://orcid.org/0000-0002-6103-6352;  Email: [email protected]
  • Authors
    • Lei Liao - 4C Air, Inc., Sunnyvale, California 94089, United States
    • Wang Xiao - 4C Air, Inc., Sunnyvale, California 94089, United States
    • Mervin Zhao - 4C Air, Inc., Sunnyvale, California 94089, United States;  Orcidhttp://orcid.org/0000-0002-7313-7150
    • Xuanze Yu - 4C Air, Inc., Sunnyvale, California 94089, United States
    • Haotian Wang - 4C Air, Inc., Sunnyvale, California 94089, United States
    • Qiqi Wang - 4C Air, Inc., Sunnyvale, California 94089, United States
    • Steven Chu - Department of Physics, Stanford University, Stanford, California 94305, United States;  Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, United States
  • Notes
    The authors declare the following competing financial interest(s): Professors Steven Chu and Yi Cui are founders and shareholders of the company 4C Air, Inc. They are inventors on patent PCT /US2015/065608. All other authors are employees of 4C Air, Inc.

Acknowledgments

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We would like to thank L. Chu and A. Price at Stanford Medicine for the helpful discussion.

References

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This article references 39 other publications.

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    Dong, E.; Du, H.; Gardner, L. An Interactive Web-Based Dashboard to Track COVID-19 in Real Time. Lancet Infect. Dis. 2020, 20, 533– 534,  DOI: 10.1016/S1473-3099(20)30120-1
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    An interactive web-based dashboard to track COVID-19 in real time
    Dong, Ensheng; Du, Hongru; Gardner, Lauren
    Lancet 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.
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  2. 2
    Zhou, P.; Yang, X.-L.; Wang, X.-G.; Hu, B.; Zhang, L.; Zhang, W.; Si, H.-R.; Zhu, Y.; Li, B.; Huang, C.-L.; Chen, H.-D.; Chen, J.; Luo, Y.; Guo, H.; Jiang, R.-D.; Liu, M.-Q.; Chen, Y.; Shen, X.-R.; Wang, X.; Zheng, X.-S. A Pneumonia Outbreak Associated with a New Coronavirus of Probable Bat Origin. Nature 2020, 579, 270– 273,  DOI: 10.1038/s41586-020-2012-7
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    A pneumonia outbreak associated with a new coronavirus of probable bat origin
    Zhou, 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-Li
    Nature (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.
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  3. 3
    Wu, F.; Zhao, S.; Yu, B.; Chen, Y.-M.; Wang, W.; Song, Z.-G.; Hu, Y.; Tao, Z.-W.; Tian, J.-H.; Pei, Y.-Y.; Yuan, M.-L.; Zhang, Y.-L.; Dai, F.-H.; Liu, Y.; Wang, Q.-M.; Zheng, J.-J.; Xu, L.; Holmes, E. C.; Zhang, Y.-Z. A New Coronavirus Associated with Human Respiratory Disease in China. Nature 2020, 579, 265– 269,  DOI: 10.1038/s41586-020-2008-3
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    3
    A new coronavirus associated with human respiratory disease in China
    Wu, 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-Zhen
    Nature (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.
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    Letko, 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, 562– 569,  DOI: 10.1038/s41564-020-0688-y
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    Functional assessment of cell entry and receptor usage for SARS-CoV-2 and other lineage B betacoronaviruses
    Letko, Michael; Marzi, Andrea; Munster, Vincent
    Nature 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.
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  5. 5
    Guan, W.-J.; Ni, Z.-Y.; Hu, Y.; Liang, W.-H.; Ou, C.-Q.; He, J.-X.; Liu, L.; Shan, H.; Lei, C.-L.; Hui, D. S. C.; Du, B.; Li, L.-J.; Zeng, G.; Yuen, K.-Y.; Chen, R.-C.; Tang, C.-L.; Wang, T.; Chen, P.-Y.; Xiang, J.; Li, S.-Y. Clinical Characteristics of Coronavirus Disease 2019 in China. N. Engl. J. Med. 2020, 382, 1708– 1720,  DOI: 10.1056/NEJMoa2002032
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    Clinical characteristics of coronavirus disease 2019 in China
    Guan, 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.
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  6. 6
    Holshue, M. L.; DeBolt, C.; Lindquist, S.; Lofy, K. H.; Wiesman, J.; Bruce, H.; Spitters, C.; Ericson, K.; Wilkerson, S.; Tural, A.; Diaz, G.; Cohn, A.; Fox, L. A.; Patel, A.; Gerber, S. I.; Kim, L.; Tong, S.; Lu, X.; Lindstrom, S.; Pallansch, M. A. First Case of 2019 Novel Coronavirus in the United States. N. Engl. J. Med. 2020, 382, 929– 936,  DOI: 10.1056/NEJMoa2001191
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    First case of 2019 novel coronavirus in the United States
    Holshue, Michelle L.; DeBolt, Chas; Lindquist, Scott; Lofy, Kathy H.; Wiesman, John; Bruce, Hollianne; Spitters, Christopher; Ericson, Keith; Wilkerson, Sara; Tural, Ahmet; Diaz, George; Cohn, Amanda; Fox, LeAnne; Patel, Anita; Gerber, Susan I.; Kim, Lindsay; Tong, Suxiang; Lu, Xiaoyan; Lindstrom, Steve; Pallansch, Mark A.; Weldon, William C.; Biggs, Holly M.; Uyeki, Timothy M.; Pillai, Satish K.
    New England Journal of Medicine (2020), 382 (10), 929-936CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)
    An outbreak of novel coronavirus (2019-nCoV) that began in Wuhan, China, has spread rapidly, with cases now confirmed in multiple countries. We report the first case of 2019-nCoV infection confirmed in the United States and describe the identification, diagnosis, clin. course, and management of the case, including the patient's initial mild symptoms at presentation with progression to pneumonia on day 9 of illness. This case highlights the importance of close coordination between clinicians and public health authorities at the local, state, and federal levels, as well as the need for rapid dissemination of clin. information related to the care of patients with this emerging infection.
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  7. 7
    Zhu, N.; Zhang, D.; Wang, W.; Li, X.; Yang, B.; Song, J.; Zhao, X.; Huang, B.; Shi, W.; Lu, R.; Niu, P.; Zhan, F.; Ma, X.; Wang, D.; Xu, W.; Wu, G.; Gao, G. F.; Tan, W. A Novel Coronavirus from Patients with Pneumonia in China, 2019. N. Engl. J. Med. 2020, 382, 727– 733,  DOI: 10.1056/NEJMoa2001017
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    A novel coronavirus from patients with pneumonia in China, 2019
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    New England Journal of Medicine (2020), 382 (8), 727-733CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)
    In Dec. 2019, a cluster of patients with pneumonia of unknown cause was linked to a seafood wholesale market in Wuhan, China. A previously unknown betacoronavirus was discovered through the use of unbiased sequencing in samples from patients with pneumonia. Human airway epithelial cells were used to isolate a novel coronavirus, named 2019-nCoV, which formed a clade within the subgenus sarbecovirus, Orthocoronavirinae subfamily. Different from both MERS-CoV and SARS-CoV, 2019-nCoV is the seventh member of the family of coronaviruses that infect humans. Enhanced surveillance and further investigation are ongoing. Complete genome sequences of the three novel coronaviruses were submitted to GISAID (BetaCoV/Wuhan/ IVDC-HB-01/2019, accession ID: EPI_ISL_402119; BetaCoV/Wuhan/IVDC-HB-04/2020, accession ID: EPI_ISL_402120; BetaCoV/Wuhan/IVDC-HB-05/2019, accession ID: EPI_ISL_402121).
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    Wang, F. S.; Zhang, C. What to Do Next to Control the 2019-NCoV Epidemic?. Lancet 2020, 395, 391– 393,  DOI: 10.1016/S0140-6736(20)30300-7
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    What to do next to control the 2019-nCoV epidemic?
    Wang, Fu-Sheng; Zhang, Chao
    Lancet (2020), 395 (10222), 391-393CODEN: LANCAO; ISSN:0140-6736. (Elsevier Ltd.)
    A review on COVID-19 epidemic.
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    The authors report the potential person-to-person transmission of SARSCoV-2 from an asymptomatic carrier with normal chest computed tomog. (CT) findings.
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    Proceedings of the National Academy of Sciences of the United States of America (2018), 115 (5), 1081-1086CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    Little is known about the amt. and infectiousness of influenza virus shed into exhaled breath. This contributes to uncertainty about the importance of airborne influenza transmission. We screened 355 symptomatic volunteers with acute respiratory illness and report 142 cases with confirmed influenza infection who provided 218 paired nasopharyngeal (NP) and 30-min breath samples (coarse >5-μm and fine ≤5-μm fractions) on days 1-3 after symptom onset. We assessed viral RNA copy no. for all samples and cultured NP swabs and fine aerosols. We recovered infectious virus from 52 (39%) of the fine aerosols and 150 (89%) of the NP swabs with valid cultures. The geometric mean RNA copy nos. were 3.8 × 104/30-min fine-, 1.2 × 104/30-min coarse-aerosol sample, and 8.2 × 108 per NP swab. Fine- and coarse-aerosol viral RNA were pos. assocd. with body mass index and no. of coughs and neg. assocd. with increasing days since symptom onset in adjusted models. Fine-aerosol viral RNA was also pos. assocd. with having influenza vaccination for both the current and prior season. NP swab viral RNA was pos. assocd. with upper respiratory symptoms and neg. assocd. with age but was not significantly assocd. with fine- or coarse-aerosol viral RNA or their predictors. Sneezing was rare, and sneezing and coughing were not necessary for infectious aerosol generation. Our observations suggest that influenza infection in the upper and lower airways are compartmentalized and independent.
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    Measurements of airborne influenza virus in aerosol particles from human coughs
    Lindsley, William G.; Blachere, Francoise M.; Thewlis, Robert E.; Vishnu, Abhishek; Davis, Kristina A.; Cao, Gang; Palmer, Jan E.; Clark, Karen E.; Fisher, Melanie A.; Khakoo, Rashida; Beezhold, Donald H.
    PLoS One (2010), 5 (11), e15100CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
    Influenza is thought to be communicated from person to person by multiple pathways. However, the relative importance of different routes of influenza transmission is unclear. To better understand the potential for the airborne spread of influenza, we measured the amt. and size of aerosol particles contg. influenza virus that were produced by coughing. Subjects were recruited from patients presenting at a student health clinic with influenza-like symptoms. Nasopharyngeal swabs were collected from the volunteers and they were asked to cough three times into a spirometer. After each cough, the cough-generated aerosol was collected using a NIOSH two-stage bioaerosol cyclone sampler or an SKC BioSampler. The amt. of influenza viral RNA contained in the samplers was analyzed using quant. real-time reverse-transcription PCR (qPCR) targeting the matrix gene M1. For half of the subjects, viral plaque assays were performed on the nasopharyngeal swabs and cough aerosol samples to det. if viable virus was present. 58 Subjects were tested, of whom 47 were pos. for influenza virus by qPCR. Influenza viral RNA was detected in coughs from 38 of these subjects (81%). 35% Of the influenza RNA was contained in particles >4 μm in aerodynamic diam., while 23% was in particles 1 to 4 μm and 42% in particles <1 μm. Viable influenza virus was detected in the cough aerosols from 2 of 21 subjects with influenza. These results show that coughing by influenza patients emits aerosol particles contg. influenza virus and that much of the viral RNA is contained within particles in the respirable size range. The results support the idea that the airborne route may be a pathway for influenza transmission, esp. in the immediate vicinity of an influenza patient. Further research is needed on the viability of airborne influenza viruses and the risk of transmission.
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    Matsuyama, S.; Nao, N.; Shirato, K.; Kawase, M.; Saito, S.; Takayama, I.; Nagata, N.; Sekizuka, T.; Katoh, H.; Kato, F.; Sakata, M.; Tahara, M.; Kutsuna, S.; Ohmagari, N.; Kuroda, M.; Suzuki, T.; Kageyama, T.; Takeda, M. Enhanced Isolation of SARS-CoV-2 by TMPRSS2- Expressing Cells. Proc. Natl. Acad. Sci. U. S. A. 2020, 117, 7001– 7003,  DOI: 10.1073/pnas.2002589117
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    Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells
    Matsuyama, Shutoku; Nao, Naganori; Shirato, Kazuya; Kawase, Miyuki; Saito, Shinji; Takayama, Ikuyo; Nagata, Noriyo; Sekizuka, Tsuyoshi; Katoh, Hiroshi; Kato, Fumihiro; Sakata, Masafumi; Tahara, Maino; Kutsuna, Satoshi; Ohmagari, Norio; Kuroda, Makoto; Suzuki, Tadaki; Kageyama, Tsutomu; Takeda, Makoto
    Proceedings of the National Academy of Sciences of the United States of America (2020), 117 (13), 7001-7003CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
    A novel betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which caused a large respiratory outbreak in Wuhan, China in Dec. 2019, is currently spreading across many countries globally. Here, we show that a TMPRSS2-expressing VeroE6 cell line is highly susceptible to SARS-CoV-2 infection, making it useful for isolating and propagating SARS-CoV-2. Our results reveal that, in common with SARS- and Middle East respiratory syndrome-CoV, SARS-CoV-2 infection is enhanced by TMPRSS2.
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    Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?
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    American journal of infection control (2006), 34 (2), 51-7 ISSN:0196-6553.
    BACKGROUND: Respiratory protection devices are used to protect the wearers from inhaling particles suspended in the air. Filtering face piece respirators are usually tested utilizing nonbiologic particles, whereas their use often aims at reducing exposure to biologic aerosols, including infectious agents such as viruses and bacteria. METHODS: The performance of 2 types of N95 half-mask, filtering face piece respirators and 2 types of surgical masks were determined. The collection efficiency of these respiratory protection devices was investigated using MS2 virus (a nonharmful simulant of several pathogens). The virions were detected in the particle size range of 10 to 80 nm. RESULTS: The results indicate that the penetration of virions through the National Institute for Occupational Safety and Health (NIOSH)-certified N95 respirators can exceed an expected level of 5%. As anticipated, the tested surgical masks showed a much higher particle penetration because they are known to be less efficient than the N95 respirators. The 2 surgical masks, which originated from the same manufacturer, showed tremendously different penetration levels of the MS2 virions: 20.5% and 84.5%, respectively, at an inhalation flow rate of 85 L/min. CONCLUSION: The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm. It should be noted that the surgical masks are primarily designed to protect the environment from the wearer, whereas the respirators are supposed to protect the wearer from the environment.
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    The SARS-coronavirus (SARS-CoV) is a newly emerged, highly pathogenic agent that caused over 8,000 human infections with nearly 800 deaths between November 2002 and September 2003. While direct person-to-person transmission via respiratory droplets accounted for most cases, other modes have not been ruled out. Faecal shedding is common and prolonged and has caused an outbreak in Hong Kong. We studied the stability of SARS-CoV under different conditions, both in suspension and dried on surfaces, in comparison with other human-pathogenic viruses, including human coronavirus HCoV-229E. In suspension, HCoV-229E gradually lost its infectivity completely while SARS-CoV retained its infectivity for up to 9 days; in the dried state, survival times were 24 h versus 6 days. Thermal inactivation at 56 degrees C was highly effective in the absence of protein, reducing the virus titre to below detectability; however, the addition of 20% protein exerted a protective effect resulting in residual infectivity. If protein-containing solutions are to be inactivated, heat treatment at 60 degrees C for at least 30 min must be used. Different fixation procedures, e.g. for the preparation of immunofluorescence slides, as well as chemical means of virus inactivation commonly used in hospital and laboratory settings were generally found to be effective. Our investigations confirm that it is possible to care for SARS patients and to conduct laboratory scientific studies on SARS-CoV safely. Nevertheless, the agents tenacity is considerably higher than that of HCoV-229E, and should SARS re-emerge, increased efforts need to be devoted to questions of environmental hygiene.
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    Disposable N95 filtering facepiece respirators (FFRs) certified by the National Institute for Occupational Safety and Health (NIOSH) are widely used by healthcare workers to reduce exposures to infectious biol. aerosols. There is currently major concern among public health officials about a possible shortage of N95 FFRs during an influenza pandemic. Decontamination and reuse of FFRs is a possible strategy for extending FFR supplies in an emergency; however, the NIOSH respirator certification process does not currently include provisions for decontamination and reuse. Recent studies have investigated the lab. performance (filter aerosol penetration and filter airflow resistance) and phys. integrity of FFRs following one-cycle (1X) processing of various decontamination treatments. The studies found that a single application of some methods did not adversely affect lab. performance. In the event that healthcare facilities experience dramatic shortages of FFR supplies, multiple decontamination processing may become necessary. This study investigates three-cycle (3X) processing of eight different methods: UV germicidal irradn., ethylene oxide, hydrogen peroxide gas plasma, hydrogen peroxide vapor, microwave-oven-generated steam, bleach, liq. hydrogen peroxide, and moist heat incubation (pasteurization). A four-hour 3X submersion of FFR in deionized water was performed for comparison (control). Following 3X treatment by each decontamination and control method, FFRs were evaluated for changes in phys. appearance, odor, and lab. filtration performance. Only the hydrogen peroxide gas plasma treatment resulted in mean penetration levels > 5% for four of the six FFR models; FFRs treated by the seven other methods and the control samples had expected levels of filter aerosol penetration (< 5%) and filter airflow resistance. Phys. damage varied by treatment method. Further research is still needed before any specific decontamination methods can be recommended.
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    Evaluation of Five Decontamination Methods for Filtering Facepiece Respirators
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    Concerns have been raised regarding the availability of National Institute for Occupational Safety and Health (NIOSH)-certified N95 filtering facepiece respirators (FFRs) during an influenza pandemic. One possible strategy to mitigate a respirator shortage is to reuse FFRs following a biol. decontamination process to render infectious material on the FFR inactive. However, little data exist on the effects of decontamination methods on respirator integrity and performance. This study evaluated five decontamination methods [UV germicidal irradn. (UVGI), ethylene oxide, vaporized hydrogen peroxide (VHP), microwave oven irradn., and bleach] using nine models of NIOSH-certified respirators (three models each of N95 FFRs, surgical N95 respirators, and P100 FFRs) to det. which methods should be considered for future research studies. Following treatment by each decontamination method, the FFRs were evaluated for changes in phys. appearance, odor, and lab. performance (filter aerosol penetration and filter airflow resistance). Addnl. expts. (dry heat lab. oven exposures, off-gassing, and FFR hydrophobicity) were subsequently conducted to better understand material properties and possible health risks to the respirator user following decontamination. However, this study did not assess the efficiency of the decontamination methods to inactivate viable microorganisms. Microwave oven irradn. melted samples from two FFR models. The remainder of the FFR samples that had been decontaminated had expected levels of filter aerosol penetration and filter airflow resistance. The scent of bleach remained noticeable following overnight drying and low levels of chlorine gas were found to off-gas from bleach-decontaminated FFRs when rehydrated with deionized water. UVGI, ethylene oxide (EtO), and VHP were found to be the most promising decontamination methods; however, concerns remain about the throughput capabilities for EtO and VHP. Further research is needed before any specific decontamination methods can be recommended.
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    A review and discussion of prevention, control, diagnosis, and treatment of COVID-19. Topics include: the etiol. of SARS-CoV-2 coronavirus; pathogenicity of SARS-CoV-2; COVID-19 detection and diagnosis; COVID-19 prevention and control; and COVID-19 clin. treatment. Vaccines in development for COVID-19 are discussed, as well as the use of traditional Chinese and Western medicines.
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    Lindsley, W. G.; Martin, S. B.; Thewlis, R. E.; Sarkisian, K.; Nwoko, J. O.; Mead, K. R.; Noti, J. D. Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity. J. Occup. Environ. Hyg. 2015, 12, 509– 517,  DOI: 10.1080/15459624.2015.1018518
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    Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity
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    Journal of Occupational and Environmental Hygiene (2015), 12 (8), 509-517CODEN: JOEHA2; ISSN:1545-9624. (Taylor & Francis, Inc.)
    The ability to disinfect and reuse disposable N95 filtering facepiece respirators (FFRs) may be needed during a pandemic of an infectious respiratory disease such as influenza. UV germicidal irradn. (UVGI) is one possible method for respirator disinfection. However, UV radiation degrades polymers, which presents the possibility that UVGI exposure could degrade the ability of a disposable respirator to protect the worker. To study this, we exposed both sides of material coupons and respirator straps from four models of N95 FFRs to UVGI doses from 120-950 J/cm2. We then tested the particle penetration, flow resistance, and bursting strengths of the individual respirator coupon layers, and the breaking strength of the respirator straps. We found that UVGI exposure led to a small increase in particle penetration (up to 1.25%) and had little effect on the flow resistance. UVGI exposure had a more pronounced effect on the strengths of the respirator materials. At the higher UVGI doses, the strength of the layers of respirator material was substantially reduced (in some cases, by >90%). The changes in the strengths of the respirator materials varied considerably among the different models of respirators. UVGI had less of an effect on the respirator straps; a dose of 2360 J/cm2 reduced the breaking strength of the straps by 20-51%. Our results suggest that UVGI could be used to effectively disinfect disposable respirators for reuse, but the max. no. of disinfection cycles will be limited by the respirator model and the UVGI dose required to inactivate the pathogen.
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    Price, A. Dp.; Cui, Y.; Liao, L.; Xiao, W.; Yu, X.; Wang, H.; Zhao, M.; Wang, Q.; Chu, S.; Chu, L. F. Is the Fit of N95 Facial Masks Effected by Disinfection? A Study of Heat and UV Disinfection Methods Using the OSHA Protocol Fit Test. medRxiv, 2020. https://www.medrxiv.org/content/10.1101/2020.04.14.20062810v1 (accessed 2020/04/28).
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    Bergman, M. S.; Viscusi, D. J.; Zhuang, Z.; Palmiero, A. J.; Powell, J. B.; Shaffer, R. E. Impact of Multiple Consecutive Donnings on Filtering Facepiece Respirator Fit. Am. J. Infect. Control 2012, 40, 375– 380,  DOI: 10.1016/j.ajic.2011.05.003
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    Impact of multiple consecutive donnings on filtering facepiece respirator fit
    Bergman Michael S; Viscusi Dennis J; Zhuang Ziqing; Palmiero Andrew J; Powell Jeffrey B; Shaffer Ronald E
    American journal of infection control (2012), 40 (4), 375-80 ISSN:.
    BACKGROUND: A concern with reuse of National Institute for Occupational Safety and Health-certified N95 filtering facepiece respirators (FFRs) is that multiple donnings could stress FFR components, impairing fit. This study investigated the impact of multiple donnings on the facepiece fit of 6 N95 FFR models using a group of 10 experienced test subjects per model. METHODS: The TSI PORTACOUNT Plus and N95 Companion accessory were used for all tests. After qualifying by passing a standard Occupational Safety and Health Administration fit test, subjects performed up to 20 consecutive tests on an individual FFR sample using a modified protocol. Regression analyses were performed for the percentage of donnings resulting in fit factors (FFs) ≥100 for all 6 FFR models combined. RESULTS: Regression analyses showed statistical significance for donning groups 1-10, 1-15, and 1-20. The mean percentage of donnings with an FF ≥100 was 81%-93% for donning group 1-5, but dropped to 53%-75% for donning group 16-20. CONCLUSIONS: Our results show that multiple donnings had a model-dependent impact on fit for the 6 N95 models evaluated. The data suggest that 5 consecutive donnings can be performed before FFs consistently drop below 100.
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  • Abstract

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    Figure 1

    Figure 1. Transmission of SARS-CoV-2 through viral aerosols. Image of SARS-CoV-2 courtesy of the CDC.

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    Figure 2

    Figure 2. Meltblown fabrics in N95 FFRs. (A) Peeling apart a representative N95 FFR reveals multiple layers of nonwoven materials. (B) Scanning electron microscope (SEM) cross-section image reveals the middle meltblown layer has thinner fibers with thickness around 300 μm. (C) SEM image of meltblown fibers reveals a complicated randomly oriented network of fibers, with diameters in the range of ∼1–10 μm. (D) Schematic illustration of meltblown fibers (left) without and (right) with electret charging. In the left figure, smaller particles are able to pass through to the user, but particles are electrostatically captured in the case of an electret (right).

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    Figure 3

    Figure 3. The 10 treatment cycle evolution of filtration characteristics. (A) Efficiency evolution where it is clear that steam treatment results in a degradation of efficiency. (B) Pressure drop evolution where it is not apparent that any structure or morphology change has occurred in the meltblown fabrics.

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    Figure 4

    Figure 4. Temperature and humidity evolution of meltblown and FFR filtration characteristics. (A, B) Evolution of meltblown fabrics’ filtration characteristics at 85 °C under different humidities, efficiency (A) and pressure drop (B). (C, D) Evolution of filtration characteristics on a meltblown fabric under 85 °C, 30% RH, efficiency (C) and pressure drop (D). (E, F) Evolution of the filtration characteristics on an N95-level FFRs with 85 °C, under 30% and 100% RH (measured at a flow rate of 85 L/min), efficiency (E) and pressure drop (F). The left-to-right of all FFR brands is as follows: (1) initial (leftmost, solid pattern, tested in ambient conditions), (2) 85 °C, 30% RH 10 cycles, (3) 85 °C, 30% RH 20 cycles, (4) 85 °C, 100% RH 10 cycles, and (5) 85 °C, 100% RH 20 cycles. (G, H) Temperature dependence of meltblown fabrics’ filtration characteristics over 20 cycles with RH < 30%, efficiency (G) and pressure drop (H).

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    Figure 5

    Figure 5. Effect of UVGI on meltblown filtration characteristics. (A) Efficiency of meltblown fabric that slightly changes after 10 cycles of UVGI. (B) Pressure drop after UVGI treatments remains similar. The larger error bar in the initial data is due to the meltblown fabric originating from various locations on the roll, whereas the meltblown fabrics used in the treatment originated from a similar location on the roll.

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  • References

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      Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community
      Yan, Jing; Grantham, Michael; Pantelic, Jovan; Bueno de Mesquita, P. Jacob; Albert, Barbara; Liu, Fengjie; Ehrman, Sheryl; Milton, Donald K.
      Proceedings of the National Academy of Sciences of the United States of America (2018), 115 (5), 1081-1086CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      Little is known about the amt. and infectiousness of influenza virus shed into exhaled breath. This contributes to uncertainty about the importance of airborne influenza transmission. We screened 355 symptomatic volunteers with acute respiratory illness and report 142 cases with confirmed influenza infection who provided 218 paired nasopharyngeal (NP) and 30-min breath samples (coarse >5-μm and fine ≤5-μm fractions) on days 1-3 after symptom onset. We assessed viral RNA copy no. for all samples and cultured NP swabs and fine aerosols. We recovered infectious virus from 52 (39%) of the fine aerosols and 150 (89%) of the NP swabs with valid cultures. The geometric mean RNA copy nos. were 3.8 × 104/30-min fine-, 1.2 × 104/30-min coarse-aerosol sample, and 8.2 × 108 per NP swab. Fine- and coarse-aerosol viral RNA were pos. assocd. with body mass index and no. of coughs and neg. assocd. with increasing days since symptom onset in adjusted models. Fine-aerosol viral RNA was also pos. assocd. with having influenza vaccination for both the current and prior season. NP swab viral RNA was pos. assocd. with upper respiratory symptoms and neg. assocd. with age but was not significantly assocd. with fine- or coarse-aerosol viral RNA or their predictors. Sneezing was rare, and sneezing and coughing were not necessary for infectious aerosol generation. Our observations suggest that influenza infection in the upper and lower airways are compartmentalized and independent.
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    13. 13
      Lindsley, W. G.; Blachere, F. M.; Thewlis, R. E.; Vishnu, A.; Davis, K. A.; Cao, G.; Palmer, J. E.; Clark, K. E.; Fisher, M. A.; Khakoo, R.; Beezhold, D. H. Measurements of Airborne Influenza Virus in Aerosol Particles from Human Coughs. PLoS One 2010, 5 (5), e15100,  DOI: 10.1371/journal.pone.0015100
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      Measurements of airborne influenza virus in aerosol particles from human coughs
      Lindsley, William G.; Blachere, Francoise M.; Thewlis, Robert E.; Vishnu, Abhishek; Davis, Kristina A.; Cao, Gang; Palmer, Jan E.; Clark, Karen E.; Fisher, Melanie A.; Khakoo, Rashida; Beezhold, Donald H.
      PLoS One (2010), 5 (11), e15100CODEN: POLNCL; ISSN:1932-6203. (Public Library of Science)
      Influenza is thought to be communicated from person to person by multiple pathways. However, the relative importance of different routes of influenza transmission is unclear. To better understand the potential for the airborne spread of influenza, we measured the amt. and size of aerosol particles contg. influenza virus that were produced by coughing. Subjects were recruited from patients presenting at a student health clinic with influenza-like symptoms. Nasopharyngeal swabs were collected from the volunteers and they were asked to cough three times into a spirometer. After each cough, the cough-generated aerosol was collected using a NIOSH two-stage bioaerosol cyclone sampler or an SKC BioSampler. The amt. of influenza viral RNA contained in the samplers was analyzed using quant. real-time reverse-transcription PCR (qPCR) targeting the matrix gene M1. For half of the subjects, viral plaque assays were performed on the nasopharyngeal swabs and cough aerosol samples to det. if viable virus was present. 58 Subjects were tested, of whom 47 were pos. for influenza virus by qPCR. Influenza viral RNA was detected in coughs from 38 of these subjects (81%). 35% Of the influenza RNA was contained in particles >4 μm in aerodynamic diam., while 23% was in particles 1 to 4 μm and 42% in particles <1 μm. Viable influenza virus was detected in the cough aerosols from 2 of 21 subjects with influenza. These results show that coughing by influenza patients emits aerosol particles contg. influenza virus and that much of the viral RNA is contained within particles in the respirable size range. The results support the idea that the airborne route may be a pathway for influenza transmission, esp. in the immediate vicinity of an influenza patient. Further research is needed on the viability of airborne influenza viruses and the risk of transmission.
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      Singing and the dissemination of tuberculosis
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      42 CFR Part 84: Respiratory protective devices implications for tuberculosis protection
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      Matsuyama, S.; Nao, N.; Shirato, K.; Kawase, M.; Saito, S.; Takayama, I.; Nagata, N.; Sekizuka, T.; Katoh, H.; Kato, F.; Sakata, M.; Tahara, M.; Kutsuna, S.; Ohmagari, N.; Kuroda, M.; Suzuki, T.; Kageyama, T.; Takeda, M. Enhanced Isolation of SARS-CoV-2 by TMPRSS2- Expressing Cells. Proc. Natl. Acad. Sci. U. S. A. 2020, 117, 7001– 7003,  DOI: 10.1073/pnas.2002589117
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      Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells
      Matsuyama, Shutoku; Nao, Naganori; Shirato, Kazuya; Kawase, Miyuki; Saito, Shinji; Takayama, Ikuyo; Nagata, Noriyo; Sekizuka, Tsuyoshi; Katoh, Hiroshi; Kato, Fumihiro; Sakata, Masafumi; Tahara, Maino; Kutsuna, Satoshi; Ohmagari, Norio; Kuroda, Makoto; Suzuki, Tadaki; Kageyama, Tsutomu; Takeda, Makoto
      Proceedings of the National Academy of Sciences of the United States of America (2020), 117 (13), 7001-7003CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
      A novel betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which caused a large respiratory outbreak in Wuhan, China in Dec. 2019, is currently spreading across many countries globally. Here, we show that a TMPRSS2-expressing VeroE6 cell line is highly susceptible to SARS-CoV-2 infection, making it useful for isolating and propagating SARS-CoV-2. Our results reveal that, in common with SARS- and Middle East respiratory syndrome-CoV, SARS-CoV-2 infection is enhanced by TMPRSS2.
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      Bałazy, A.; Toivola, M.; Adhikari, A.; Sivasubramani, S. K.; Reponen, T.; Grinshpun, S. A. Do N95 Respirators Provide 95% Protection Level against Airborne Viruses, and How Adequate Are Surgical Masks?. Am. J. Infect. Control 2006, 34, 51– 57,  DOI: 10.1016/j.ajic.2005.08.018
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      19
      Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks?
      Balazy Anna; Toivola Mika; Adhikari Atin; Sivasubramani Satheesh K; Reponen Tiina; Grinshpun Sergey A
      American journal of infection control (2006), 34 (2), 51-7 ISSN:0196-6553.
      BACKGROUND: Respiratory protection devices are used to protect the wearers from inhaling particles suspended in the air. Filtering face piece respirators are usually tested utilizing nonbiologic particles, whereas their use often aims at reducing exposure to biologic aerosols, including infectious agents such as viruses and bacteria. METHODS: The performance of 2 types of N95 half-mask, filtering face piece respirators and 2 types of surgical masks were determined. The collection efficiency of these respiratory protection devices was investigated using MS2 virus (a nonharmful simulant of several pathogens). The virions were detected in the particle size range of 10 to 80 nm. RESULTS: The results indicate that the penetration of virions through the National Institute for Occupational Safety and Health (NIOSH)-certified N95 respirators can exceed an expected level of 5%. As anticipated, the tested surgical masks showed a much higher particle penetration because they are known to be less efficient than the N95 respirators. The 2 surgical masks, which originated from the same manufacturer, showed tremendously different penetration levels of the MS2 virions: 20.5% and 84.5%, respectively, at an inhalation flow rate of 85 L/min. CONCLUSION: The N95 filtering face piece respirators may not provide the expected protection level against small virions. Some surgical masks may let a significant fraction of airborne viruses penetrate through their filters, providing very low protection against aerosolized infectious agents in the size range of 10 to 80 nm. It should be noted that the surgical masks are primarily designed to protect the environment from the wearer, whereas the respirators are supposed to protect the wearer from the environment.
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      Wall, T. H.; Hansen, P. E. Filtering Web for Face Masks and Face Masks Made Therefrom. US3316904A, 1967.
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      Ghosal, A.; Sinha-Ray, S.; Yarin, A. L.; Pourdeyhimi, B. Numerical Prediction of the Effect of Uptake Velocity on Three-Dimensional Structure, Porosity and Permeability of Meltblown Nonwoven Laydown. Polymer 2016, 85, 19– 27,  DOI: 10.1016/j.polymer.2016.01.013
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      Numerical prediction of the effect of uptake velocity on three-dimensional structure, porosity and permeability of meltblown nonwoven laydown
      Ghosal, Arkaprovo; Sinha-Ray, Suman; Yarin, Alexander L.; Pourdeyhimi, Behnam
      Polymer (2016), 85 (), 19-27CODEN: POLMAG; ISSN:0032-3861. (Elsevier Ltd.)
      This work describes the first detailed model of meltblowing process which allows prediction of such integral laydown properties as thickness, porosity and permeability. Also, such laydown properties as the detailed three-dimensional micro-structure, fiber-size distribution and polymer mass distribution are predicted. The effects of the governing meltblowing parameters on the variation of all these laydown properties are accounted for, with the influence of the collector screen velocity being in focus. For this aim numerical solns. of the system of quasi-one-dimensional equations of the dynamics of free liq. polymer jets moving, cooling and solidifying when driven by surrounding air jet are constructed. Multiple polymer jets are considered simultaneously when they are deposited on a moving screen and forming a nonwoven laydown. The results reveal the three-dimensional configuration of the laydown and, in particular, its porosity and permeability, as well as elucidate the dependence of the laydown structure on the forming conditions, in particular, on the velocity of the screen motion. It is shown and explained how an increase in the velocity of the collector screen increases porosity and permeability of the meltblown nonwoven laydown.
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      Kubik, D. A.; Davis, C. I. Melt-Blown Fibrous Electrets. US4215682A, 1980.
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      Angadjivand, S. A.; Jones, M. E.; Meyer, D. E. Electret Filter Media. US6119691A, 1994.
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      Barrett, L. W.; Rousseau, A. D. Aerosol Loading Performance of Electret Filter Media. Am. Ind. Hyg. Assoc. J. 1998, 59, 532– 539,  DOI: 10.1080/15428119891010703
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      Ranney, M. L.; Griffeth, V.; Jha, A. K. Critical Supply Shortages — The Need for Ventilators and Personal Protective Equipment during the Covid-19 Pandemic. N. Engl. J. Med. 2020, 382, e41  DOI: 10.1056/NEJMp2006141
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      Critical supply shortages - the need for ventilators and personal protective equipment during the Covid-19 pandemic
      Ranney, Megan L.; Griffeth, Valerie; Jha, Ashish K.
      New England Journal of Medicine (2020), 382 (18), e41CODEN: NEJMAG; ISSN:1533-4406. (Massachusetts Medical Society)
      As the United States braces for a growing wave of patients with Covid-19 in our hospitals and ICUs, we must ensure that we have the key equipment needed to care for patients and to keep our health care workforce safe. Failure to act in a coordinated manner would keep many patients from getting the care they need and would lead to the situation we see in Italy, in which frontline clinicians are making difficult decisions about who will and who won't receive care. Furthermore, without adequate PPE, health care workers will get sick, endangering the functioning of the entire health care system. The human and economic costs of that scenario should not be underestimated.
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      van 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.; Lloyd-Smith, J. O.; de Wit, E.; Munster, V. J. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N. Engl. J. Med. 2020, 382, 1564– 1567,  DOI: 10.1056/NEJMc2004973
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      Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1
      van 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 O
      The New England journal of medicine (2020), 382 (16), 1564-1567 ISSN:.
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      Rutala, W. A.; Weber, D. J. Guideline for Disinfection and Sterilization in Healthcare Facilities (2008); Centers for Disease Control and Prevention: Atlanta, GA, 2008; pp 1– 163. https://www.cdc.gov/infectioncontrol/guidelines/disinfection/index.html (accessed 2020/03/28).
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      Darnell, M. E. R.; Subbarao, K.; Feinstone, S. M.; Taylor, D. R. Inactivation of the Coronavirus That Induces Severe Acute Respiratory Syndrome, SARS-CoV. J. Virol. Methods 2004, 121, 85– 91,  DOI: 10.1016/j.jviromet.2004.06.006
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      Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV
      Darnell, Miriam E. R.; Subbarao, Kanta; Feinstone, Stephen M.; Taylor, Deborah R.
      Journal of Virological Methods (2004), 121 (1), 85-91CODEN: JVMEDH; ISSN:0166-0934. (Elsevier B.V.)
      Severe acute respiratory syndrome (SARS) is a life-threatening disease caused by a novel coronavirus termed SARS-CoV. Due to the severity of this disease, the World Health Organization (WHO) recommends that manipulation of active viral cultures of SARS-CoV be performed in containment labs. at biosafety level 3 (BSL3). The virus was inactivated by UV light (UV) at 254 nm, heat treatment of 65 or greater, alk. (pH > 12) or acidic (pH < 3) conditions, formalin and glutaraldehyde treatments. We describe the kinetics of these efficient viral inactivation methods, which will allow research with SARS-CoV contg. materials, that are rendered non-infectious, to be conducted at reduced safety levels.
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      Rabenau, H. F.; Cinatl, J.; Morgenstern, B.; Bauer, G.; Preiser, W.; Doerr, H. W. Stability and Inactivation of SARS Coronavirus. Med. Microbiol. Immunol. 2005, 194, 1– 6,  DOI: 10.1007/s00430-004-0219-0
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      Stability and inactivation of SARS coronavirus
      Rabenau H F; Cinatl J; Morgenstern B; Bauer G; Preiser W; Doerr H W
      Medical microbiology and immunology (2005), 194 (1-2), 1-6 ISSN:0300-8584.
      The SARS-coronavirus (SARS-CoV) is a newly emerged, highly pathogenic agent that caused over 8,000 human infections with nearly 800 deaths between November 2002 and September 2003. While direct person-to-person transmission via respiratory droplets accounted for most cases, other modes have not been ruled out. Faecal shedding is common and prolonged and has caused an outbreak in Hong Kong. We studied the stability of SARS-CoV under different conditions, both in suspension and dried on surfaces, in comparison with other human-pathogenic viruses, including human coronavirus HCoV-229E. In suspension, HCoV-229E gradually lost its infectivity completely while SARS-CoV retained its infectivity for up to 9 days; in the dried state, survival times were 24 h versus 6 days. Thermal inactivation at 56 degrees C was highly effective in the absence of protein, reducing the virus titre to below detectability; however, the addition of 20% protein exerted a protective effect resulting in residual infectivity. If protein-containing solutions are to be inactivated, heat treatment at 60 degrees C for at least 30 min must be used. Different fixation procedures, e.g. for the preparation of immunofluorescence slides, as well as chemical means of virus inactivation commonly used in hospital and laboratory settings were generally found to be effective. Our investigations confirm that it is possible to care for SARS patients and to conduct laboratory scientific studies on SARS-CoV safely. Nevertheless, the agents tenacity is considerably higher than that of HCoV-229E, and should SARS re-emerge, increased efforts need to be devoted to questions of environmental hygiene.
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      Chin, A. W. H.; Chu, J. T. S.; Perera, M. R. A.; Hui, K. P. Y.; Yen, H.-L.; Chan, M. C. W.; Peiris, M.; Poon, L. L. M. Stability of SARS-CoV-2 in Different Environmental Conditions. Lancet Microbe 2020,  DOI: 10.1016/S2666-5247(20)30003-3
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      Bergman, M. S.; Viscusi, D. J.; Heimbuch, B. K.; Wander, J. D.; Sambol, A. R.; Shaffer, R. E. Evaluation of Multiple (3-Cycle) Decontamination Processing for Filtering Facepiece Respirators. J. Eng. Fibers Fabr. 2010, 5, 33– 41,  DOI: 10.1177/155892501000500405
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      Evaluation of multiple (3-cycle) decontamination processing for filtering facepiece respirators
      Bergman, Michael S.; Viscusi, Dennis J.; Heimbuch, Brian K.; Wander, Joseph D.; Sambol, Anthony R.; Shaffer, Ronald E.
      Journal of Engineered Fibers and Fabrics (2010), 5 (4), 33-41CODEN: JEFFBY; ISSN:1558-9250. (INDA, Association of the Nonwoven Fabrics Industry)
      Disposable N95 filtering facepiece respirators (FFRs) certified by the National Institute for Occupational Safety and Health (NIOSH) are widely used by healthcare workers to reduce exposures to infectious biol. aerosols. There is currently major concern among public health officials about a possible shortage of N95 FFRs during an influenza pandemic. Decontamination and reuse of FFRs is a possible strategy for extending FFR supplies in an emergency; however, the NIOSH respirator certification process does not currently include provisions for decontamination and reuse. Recent studies have investigated the lab. performance (filter aerosol penetration and filter airflow resistance) and phys. integrity of FFRs following one-cycle (1X) processing of various decontamination treatments. The studies found that a single application of some methods did not adversely affect lab. performance. In the event that healthcare facilities experience dramatic shortages of FFR supplies, multiple decontamination processing may become necessary. This study investigates three-cycle (3X) processing of eight different methods: UV germicidal irradn., ethylene oxide, hydrogen peroxide gas plasma, hydrogen peroxide vapor, microwave-oven-generated steam, bleach, liq. hydrogen peroxide, and moist heat incubation (pasteurization). A four-hour 3X submersion of FFR in deionized water was performed for comparison (control). Following 3X treatment by each decontamination and control method, FFRs were evaluated for changes in phys. appearance, odor, and lab. filtration performance. Only the hydrogen peroxide gas plasma treatment resulted in mean penetration levels > 5% for four of the six FFR models; FFRs treated by the seven other methods and the control samples had expected levels of filter aerosol penetration (< 5%) and filter airflow resistance. Phys. damage varied by treatment method. Further research is still needed before any specific decontamination methods can be recommended.
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      Xiao, H.; Song, Y.; Chen, G. Correlation between Charge Decay and Solvent Effect for Melt-Blown Polypropylene Electret Filter Fabrics. J. Electrost. 2014, 72, 311– 314,  DOI: 10.1016/j.elstat.2014.05.006
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      Correlation between charge decay and solvent effect for melt-blown polypropylene electret filter fabrics
      Xiao, Huiming; Song, Yeping; Chen, Gangjin
      Journal of Electrostatics (2014), 72 (4), 311-314CODEN: JOELDH; ISSN:0304-3886. (Elsevier B.V.)
      Melt-blown polypropylene electret fabrics are widely used as air filter media. However, its filtration efficiency gradually decays in application process. This paper is to investigate the correlation between filtration efficiency decay and solvent effect. Exptl. results showed that filtration efficiency displays a regular decrease when polypropylene electret fabrics were exposed to solvents in the sequence of water, ethanol, isopropanol and acetone. The results can be correlated to soly. parameter difference between polypropylene and solvent according to the Flory-Huggins swelling theory. Smaller soly. parameter difference leads to greater decay of filtration efficiency owing to greater affinity between polypropylene and solvent.
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      Nazeeri, A. I.; Hilburn, I. A.; Wu, D.-A.; Mohammed, K. A.; Badal, D. Y.; Chan, M. H. W.; Kirschvink, J. L. An Efficient Ethanol-Vacuum Method for the Decontamination and Restoration of Polypropylene Microfiber Medical Masks & Respirators. medRxiv, 2020. https://www.medrxiv.org/content/10.1101/2020.04.12.20059709v1 (accessed 2020/04/28).
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      Viscusi, D. J.; Bergman, M. S.; Eimer, B. C.; Shaffer, R. E. Evaluation of Five Decontamination Methods for Filtering Facepiece Respirators. Ann. Occup. Hyg. 2009, 53, 815– 827,  DOI: 10.1093/annhyg/mep070
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      Evaluation of Five Decontamination Methods for Filtering Facepiece Respirators
      Viscusi, Dennis J.; Bergman, Michael S.; Eimer, Benjamin C.; Shaffer, Ronald E.
      Annals of Occupational Hygiene (2009), 53 (8), 815-827CODEN: AOHYA3; ISSN:0003-4878. (Oxford University Press)
      Concerns have been raised regarding the availability of National Institute for Occupational Safety and Health (NIOSH)-certified N95 filtering facepiece respirators (FFRs) during an influenza pandemic. One possible strategy to mitigate a respirator shortage is to reuse FFRs following a biol. decontamination process to render infectious material on the FFR inactive. However, little data exist on the effects of decontamination methods on respirator integrity and performance. This study evaluated five decontamination methods [UV germicidal irradn. (UVGI), ethylene oxide, vaporized hydrogen peroxide (VHP), microwave oven irradn., and bleach] using nine models of NIOSH-certified respirators (three models each of N95 FFRs, surgical N95 respirators, and P100 FFRs) to det. which methods should be considered for future research studies. Following treatment by each decontamination method, the FFRs were evaluated for changes in phys. appearance, odor, and lab. performance (filter aerosol penetration and filter airflow resistance). Addnl. expts. (dry heat lab. oven exposures, off-gassing, and FFR hydrophobicity) were subsequently conducted to better understand material properties and possible health risks to the respirator user following decontamination. However, this study did not assess the efficiency of the decontamination methods to inactivate viable microorganisms. Microwave oven irradn. melted samples from two FFR models. The remainder of the FFR samples that had been decontaminated had expected levels of filter aerosol penetration and filter airflow resistance. The scent of bleach remained noticeable following overnight drying and low levels of chlorine gas were found to off-gas from bleach-decontaminated FFRs when rehydrated with deionized water. UVGI, ethylene oxide (EtO), and VHP were found to be the most promising decontamination methods; however, concerns remain about the throughput capabilities for EtO and VHP. Further research is needed before any specific decontamination methods can be recommended.
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      Yang, P.; Wang, X. COVID-19: A New Challenge for Human Beings. Cell. Mol. Immunol. 2020, 17, 555– 557,  DOI: 10.1038/s41423-020-0407-x
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      COVID-19: a new challenge for human beings
      Yang, Penghui; Wang, Xiliang
      Cellular & Molecular Immunology (2020), 17 (5), 555-557CODEN: CMIEAO; ISSN:1672-7681. (Nature Research)
      A review and discussion of prevention, control, diagnosis, and treatment of COVID-19. Topics include: the etiol. of SARS-CoV-2 coronavirus; pathogenicity of SARS-CoV-2; COVID-19 detection and diagnosis; COVID-19 prevention and control; and COVID-19 clin. treatment. Vaccines in development for COVID-19 are discussed, as well as the use of traditional Chinese and Western medicines.
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    36. 36
      Lindsley, W. G.; Martin, S. B.; Thewlis, R. E.; Sarkisian, K.; Nwoko, J. O.; Mead, K. R.; Noti, J. D. Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity. J. Occup. Environ. Hyg. 2015, 12, 509– 517,  DOI: 10.1080/15459624.2015.1018518
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      36
      Effects of Ultraviolet Germicidal Irradiation (UVGI) on N95 Respirator Filtration Performance and Structural Integrity
      Lindsley, William G.; Martin, Stephen B., Jr.; Thewlis, Robert E.; Sarkisian, Khachatur; Nwoko, Julian O.; Mead, Kenneth R.; Noti, John D.
      Journal of Occupational and Environmental Hygiene (2015), 12 (8), 509-517CODEN: JOEHA2; ISSN:1545-9624. (Taylor & Francis, Inc.)
      The ability to disinfect and reuse disposable N95 filtering facepiece respirators (FFRs) may be needed during a pandemic of an infectious respiratory disease such as influenza. UV germicidal irradn. (UVGI) is one possible method for respirator disinfection. However, UV radiation degrades polymers, which presents the possibility that UVGI exposure could degrade the ability of a disposable respirator to protect the worker. To study this, we exposed both sides of material coupons and respirator straps from four models of N95 FFRs to UVGI doses from 120-950 J/cm2. We then tested the particle penetration, flow resistance, and bursting strengths of the individual respirator coupon layers, and the breaking strength of the respirator straps. We found that UVGI exposure led to a small increase in particle penetration (up to 1.25%) and had little effect on the flow resistance. UVGI exposure had a more pronounced effect on the strengths of the respirator materials. At the higher UVGI doses, the strength of the layers of respirator material was substantially reduced (in some cases, by >90%). The changes in the strengths of the respirator materials varied considerably among the different models of respirators. UVGI had less of an effect on the respirator straps; a dose of 2360 J/cm2 reduced the breaking strength of the straps by 20-51%. Our results suggest that UVGI could be used to effectively disinfect disposable respirators for reuse, but the max. no. of disinfection cycles will be limited by the respirator model and the UVGI dose required to inactivate the pathogen.
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      Disinfection of Filtering Facepiece Respirators; 3M: St. Paul, MN, 2020; pp 1– 3.
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      Price, A. Dp.; Cui, Y.; Liao, L.; Xiao, W.; Yu, X.; Wang, H.; Zhao, M.; Wang, Q.; Chu, S.; Chu, L. F. Is the Fit of N95 Facial Masks Effected by Disinfection? A Study of Heat and UV Disinfection Methods Using the OSHA Protocol Fit Test. medRxiv, 2020. https://www.medrxiv.org/content/10.1101/2020.04.14.20062810v1 (accessed 2020/04/28).
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      Bergman, M. S.; Viscusi, D. J.; Zhuang, Z.; Palmiero, A. J.; Powell, J. B.; Shaffer, R. E. Impact of Multiple Consecutive Donnings on Filtering Facepiece Respirator Fit. Am. J. Infect. Control 2012, 40, 375– 380,  DOI: 10.1016/j.ajic.2011.05.003
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      Impact of multiple consecutive donnings on filtering facepiece respirator fit
      Bergman Michael S; Viscusi Dennis J; Zhuang Ziqing; Palmiero Andrew J; Powell Jeffrey B; Shaffer Ronald E
      American journal of infection control (2012), 40 (4), 375-80 ISSN:.
      BACKGROUND: A concern with reuse of National Institute for Occupational Safety and Health-certified N95 filtering facepiece respirators (FFRs) is that multiple donnings could stress FFR components, impairing fit. This study investigated the impact of multiple donnings on the facepiece fit of 6 N95 FFR models using a group of 10 experienced test subjects per model. METHODS: The TSI PORTACOUNT Plus and N95 Companion accessory were used for all tests. After qualifying by passing a standard Occupational Safety and Health Administration fit test, subjects performed up to 20 consecutive tests on an individual FFR sample using a modified protocol. Regression analyses were performed for the percentage of donnings resulting in fit factors (FFs) ≥100 for all 6 FFR models combined. RESULTS: Regression analyses showed statistical significance for donning groups 1-10, 1-15, and 1-20. The mean percentage of donnings with an FF ≥100 was 81%-93% for donning group 1-5, but dropped to 53%-75% for donning group 16-20. CONCLUSIONS: Our results show that multiple donnings had a model-dependent impact on fit for the 6 N95 models evaluated. The data suggest that 5 consecutive donnings can be performed before FFs consistently drop below 100.
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