Giardia: Risk for Children and Infants

Factors, and Section 6 Risk Assessment. Section 7 is a summary of the information and research recommendations. Section 8 lists references used to prepare the addendum. Primary references are provided except in instances where information about Giardia and giardiasis has already been summarized in EPA's current Drinking Water Criteria Document on Giardia (U.S. EPA, 1998) or previous criteria document (ICAIR, 1984). In some instances (e.g., foreign language scientific journals), abstracts are referenced. Giardiasis in infants and children can present as (1) asymptomatic infection; (2) acute diarrhea; (3) chronic diarrhea. Giardia infection is often asymptomatic for children. It is not clear whether the initial infection is acquired without producing symptoms, as infection may result in a transient, mild, diarrheal illness that passes without notice. Chronic giardiasis appears to be infrequent, but when it occurs, may persist for years, sometimes with asymptomatic periods. Giardia infection tends to be more common in children than adults. The prevalence of infection among children worldwide has been found to range from 1% to 36% and occasionally may be as high as 72% depending on the age group and country. In many developing countries, Giardia infections are acquired in early childhood, and by the age of 5 most children have been infected at least once. This may be related to frequent opportunities for exposure. In the United States, the highest incidence and prevalence of infection is found among children under 5 years of age, especially for those attending day-care centers. In two counties of Washington State, a prevalence of 7.1% was found among children aged 1 to 3 years. Bartlett et al. (1991) found that 11% of infants and toddlers tested for admission to day care centers in Arizona were already infected. In Vermont, children aged one to four years had the highest incidence rate of any age group for symptomatic Giardia infection. In nine outpatient clinics in the United States, Giardia was detected in 15% of children (2-11 5 years of age) with acute diarrhea. In British Columbia, the majority of Giardia-positive patients were also in the 1-5 year age group. Most prevalence studies have been conducted in developing countries, and additional data are needed to better assess the current prevalence of Giardia infection among children in the United States. There is no evidence that Giardia is transmitted from mother to fetus, but infants can acquire infections at an early age suggesting that mothers can infect …