Giardiasis and other intestinal parasitic infections in a Manitoba residential school for the mentally retarded.

A case of severely symptomatic giardiasis in a school for the mentally retarded prompted an epidemiologic survey of the institution. The rate of parasitic infection in the children were just under 50%. Multiple infections were common and one child harboured five different protozoa. The yield included known pathogens (Giardia lamblia, Metorchis conjunctus and Diphyllobothrium sp.), protozoa of potential pathogenicity (Dientamoeba fragilis) and other protozoa, the significance of which has yet to be determined. The prevalence of G. lamblia in the index ward was significantly higher than in a control ward matched for age and mobility of the children. The epidemiologic data suggested person-to-person transmission of G. lamblia within the institution. Recommendations for the control of protozoal intestinal infections in custodial institutions are presented.