An Outbreak of Waterborne Cryptosporidiosis in Kanagawa, Japan

An outbreak of diarrhea due to infection with Cryptosporidium occurred among the staff members and customers who visited one of the 10 public houses or a dancing school in a building in Hiratsuka, Kanagawa Prefecture, at the end of summer in 1994. The epidemiological surveys by a questionnaire revealed that 461 out of 736 persons investigated complained of cholera-like or flu-like illness. The clinical manifestations included mucous and/or watery diarrhea (96.7%), abdominal pain (61.6%), fever (54.2%: lower than 39°C= 84.1%, higher than 39°C= 15.9%), malaise (37.1%), nausea (32.8%) and headache (29.3%). The polluted drinking water was strongly suspected to be the immediate cause of infection. Although several species of pathogenic bacteria were isolated both from stool and water samples, they were not supposed to be linked to the outbreak. No known enteropathogenic virus was found in either of the samples. Oocysts of Cryptosporidium parvum were identified in 12 (48.0%) of the 25 stool samples. The oocysts were also found in tap water and other water samples from a receiving tank which was directly connected with the public waterworks, and an elevated tank on the roof, a wastewater pits, a soil pit and artesianspring water tank. These tanks and pits except for the elevated tank were built adjucent to each other on an underground floor of the building. These tanks and pits were connected with openings in the upperpart of the tank walls. These openings might have functioned to discharge excess of drinking water in the receiving tank to the wastewater pit. The water level of the wastewater pit is kept down below the openings by pumping out the sanitary sewage to the public drain. According to the declaration of the owner of the building, however, the wastewater pump was broken at the time of outbreak. Accidental malfunction of the drainage system caused contamination of drinking water with sanitary sewage through the connecting pipes.