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Asymptomatic infection with either Entamoeba histolytica or Giardia lamblia was found in 60 per cent of the residents in an institution for the mentally retarded one year after eradication of these parasites. The residents were then segregated into infected and noninfected groups and drug therapy was again successfully undertaken. The two groups remained separated except during periods of play. A one-year follow-up showed that both study and control groups were equally infected. The failure of segregation was confounded by patient age and infection with nonpathogenic parasites.

Asymptomatic infection with either Entameba histolytica or Giardia lamblia was found in 61 per cent of the residents of a dormitory in an institution for the mentally retarded; two other dormitories had rates of 20 per cent and 22 per cent. Drug therapy was successfully undertaken in all three dormitories, and environmental improvements were introduced in the heavily infected dormitory. A one-year follow-up showed a reduction in parasitic disease in two dormitories but, in the most heavily infected dormitory, infection had returned to pretreatment levels.

A passive disease report card (DRC) surveillance system failed to detect an epidemic of diarrheal disease caused by a newly identified drug-resistant strain of Shigella sonnei. The DRC system inaccurately described both the population at risk and the geographic location of cases. Specific limitations of the DRC system, including problems of underreporting and ascertainment bias, were complicated by the absence of timely data analysis and feedback to providers.