Epidemic Giardiasis at a Ski Resort

An outbreak of protracted, intermittent diarrhea, often associated with symptoms suggesting malabsorption, occurred in persons who vacationed in Aspen, Colorado, during the 1965–66 ski season. A survey of 1094 skiers showed that the characteristic illness had developed in at least 11.3 per cent. The association of Giardia lamblia with the illness, the absence of other pathogens, and the response to treatment suggest that G. lamblia was the agent responsible for the illness. Environmental studies carried out after the epidemic demonstrated contamination of well water by sewage leaking from defective pipes passing near wells. G. lamblia cysts were found in the sewage from the defective pipes and in stools from 6.9 per cent of the permanent residents of the city living in the area served by the defective sewage lines. The findings are consistent with a hypothesis of water-borne spread of giardiasis.