An Outbreak of Giardiasis in a Group of Campers

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  • Field Services Division, Bureau of Epidemiology, Center for Disease Control, Public Health Service, U. S. Department of Health, Education, and Welfare, Bureau of Disease Prevention, Utah State Division of Health, Atlanta, Georgia 30333

Thirty-four of 54 campers on a 2-week trip in mountains of Utah had diarrhea during and after their trip. Twenty-two (79%) of 28 symptomatic campers' stools examined contained Giardia lamblia cysts, whereas 4 (29%) of 14 asymptomatic campers' stools had cysts. The temporal distribution of cases and the absence of clustering among food preparation subgroups suggested a common source exposure. Although the epidemiologic data and fecal coliform counts implicated the remote mountain stream used as water source by the group as the vehicle of transmission, Giardia lamblia cysts were not recovered from stream water nor were they found in intestines or feces of sampled mammals living in the drainage area. Twenty-five other campers had stools examined before and after a subsequent hiking trip in another area of Utah; none had Giardia cysts before, but 6 (24%) had them after return. Questionnaires returned by 133 other campers showed that 5% had an illness compatible with giardiasis within 2 weeks after their trip. These surveys show that campers exposed to mountain stream water are at risk of acquiring giardiasis.