Giardiasis as a threat to backpackers in the United States: a survey of state health departments.

Forty-eight of the 50 state health departments in the United States responded to a questionnaire about giardiasis in their jurisdictions. The agencies had reports of 34348 cases during 1991 and studied 80 outbreaks in the same period. Nineteen of these outbreaks were attributed to consumption of contaminated drinking water; only two outbreaks were reported among individuals identified as campers or backpackers. Only two departments considered water-associated giardiasis to be a problem for backpackers in their jurisdiction, and neither had any data to support this concern. The surveillance data of health departments indicate that giardiasis is a common communicable disease in the United States. They do not, however, provide any evidence that wilderness water is an important cause of the disease in this country.