Cryptosporidiosis outbreaks associated with recreational water use--five states, 2006.

Cryptosporidiosis is a gastrointestinal illness caused by parasitic protozoa of the genus Cryptosporidium and can produce watery diarrhea lasting 1-3 weeks; one or two cases per 100,000 population are reported annually in the United States. Fecal-oral transmission of Cryptosporidium oocysts occurs through ingestion of contaminated drinking or recreational water, consumption of contaminated food, and contact with infected persons or animals (e.g., cattle or sheep). Unlike bacterial pathogens, Cryptosporidium oocysts are resistant to chlorine disinfection and can survive for days in treated recreational water venues (e.g., public and residential swimming pools and community and commercial water parks) despite adherence to recommended residual chlorine levels (1-3 ppm). For 2006, a total of 18 cryptosporidiosis outbreaks have been reported (as of July 24, 2007) to CDC's U.S. Waterborne Disease and Outbreak Surveillance System, compared with five outbreaks reported for 2003 and seven for 2004; data for 2005 and 2006 are not yet final. This report describes five laboratory-confirmed cryptosporidiosis outbreaks in 2006 that involved public recreational water use. The popularity of recreational water venues, the number and geographic distribution of recent cryptosporidiosis outbreaks, and the resistance of Cryptosporidium to chlorination suggest that treatment strategies for recreational water facilities need to be improved.