An outbreak of amebiasis in an institution for the mentally retarded in Japan.

The results of an epidemiological survey in a 190-patient institution for mentally retarded were reported. Twenty percent of the patients had either cysts or trophozoites of Entamoeba histolytica in their stools, and 38% were positive serologically. The amebic outbreak revealed a sex-independent but age-dependent distribution; younger patients had more serious symptoms in cases invasive amebiasis. A high prevalence of amebic infection was found in the heavily retarded patients, and the positive cases tended to concentrate in certain training classes. Further demographic analysis suggests that the amebic infection was possibly caused by abnormal behavior of heavily retarded patients.