Mass infection with Entamoeba histolytica in a Japanese institution for individuals with mental retardation: Epidemiology and control measures

After two cases of amoebic colitis were detected at an institution for the mentally retarded in the Yamagata prefecture of Japan, the prevalence and epidemiology of Entamoeba histolytica infection at the institution were investigated. When the 76 residents with mental retardation were checked by serology and stool examinations, 40 (53%) showed evidence of infection with E. histolytica (i.e. E. histolytica-specific antibodies in their serum, Entamoeba cysts in their stools, and/or E. histolytica-specific antigens in their stools). The cysts were all assumed to be those of E. histolytica since all nine of the 18 cyst-positive stool samples investigated using a PCR (that distinguishes E. histolytica from E. dispar) were found positive for this species. The E. histolytica found in the institution in Yamagata appears to have been brought into the institution, from a similar institution in Kanagawa prefecture, by a mentally retarded individual who relocated from Kanagawa to Yamagata. Isolates of E. histolytica recovered during an outbreak in the institution in Kanagawa appear genotypically identical to the genotyped isolates collected in the outbreak investigated in the present study. The 40 infected individuals in Yamagata were each treated for 10 days with metronidazole or diloxanide furoate. The residents and staff of the institution were encouraged to wash their hands more frequently and more thoroughly, and the staff were asked to clip residents' fingernails and to improve the cleanliness/sterilization of the surfaces in the institution that were most likely to be contaminated with E. histolytica (lavatories, handrails, doors, doorknobs, washrooms, clothing etc). In the last 5 years of follow-up since the instigation of these and other infection-control measures, and the last treatments, no cases of E. histolytica infection have been found in the institution. This encouraging result offers hope and guidance to those attempting to control outbreaks of E. histolytica infection in other institutions.