[An outbreak of cryptosporidiosis associated with swimming pools].

A waterborne outbreak of cryptosporidiosis occurred among visitors at a hotel with a swimming pool, gymnasium, and other sports facilities, in northern Nagano Prefecture. The outbreak began in late August, peaked on August 27 and 28, and tapered off at the beginning of September 2004. On August 30, 288 clinical cases with digestive symptoms, including watery diarrhea, vomiting, abdominal cramps and tenesmus, were reported to local authorities. Among case-patients who submitted stool samples, 74 were positive for Cryptosporidium. Descriptive epidemiology, environmental investigations, and laboratory tests suggested that a fecal accident in the swimming pool by swimmers infected before attending the summer training camp was thought to be the source of contamination, and case-patients were mostly among swimmers. Some other clinical-cases had no history of swimming in the pool during their stay and likely were infected through drinking contaminated self-made sports drinks dissolved in water from contaminated faucets and/or sinks nearby the gymnasium toilet. The sink was used to deal with the aftermath of a toilet accident at the entrance of the toilet by a swimming school attendee on August 21. This report is, to our knowledge, the first of a cryptosporidiosis outbreak associated with swimming pools in Japan.