Giardiasis is the third most commonly reported disease in New Zealand. Its incidence is highest in two groups—those aged 1–4 years and those aged 30–39. The disease is caused by the ingestion of the cysts of Giardia protozoa, typically from water contaminated with human waste. Once the cysts are inside the small intestine, they transform into trophozoites and multiply. In 1–3 weeks, explosive diarrhea hits as the intestinal lining becomes too damaged to absorb food.

In 1998, Ekramul Hoque and colleagues at the New Zealand Environmental and Occupational Health Research Centre (NEOH) undertook a study of giardiasis risk factors (Lancet 2001, 357, 1017–1018). The researchers compared patients (aged 15–64 years) who were stool-positive for Giardia between July 1998 and June 1999, to age-matched controls identified from the local phone book, looking retrospectively at events leading up to diagnosis. The NEOH researchers concentrated their efforts on factors such as water use, overseas travel, child handling, bathroom habits, water sports, and occupational exposure to human waste.

Giardiasis occurred twice as often in housewives and nursing mothers as in other occupational groups. Those who had some contact with diapers showed a similar trend. Furthermore, diaper changing led to a fourfold increase in the incidence of giardiasis, regardless of reported personal hygiene practices. Perhaps not surprisingly, in people exposed to diaper-wearing children, women had a higher incidence than men.

Because 75% of giardiasis cases are symptom-free, it is suspected that these individuals are an important source of infection. Data from local sources suggested that the rate of infection is 5 times higher in preschool children (aged 1–5 years) than in all other age groups and that even in this group, the incidence increases substantially once the children attend a childcare facility.

“The high representation of women of childbearing age,” the researchers wrote, “suggests a target group for effective health promotion.”