Reports of gastrointestinal illness from use of public pools and water parks have risen sharply in recent years, according to the Centers for Disease Control and Prevention. The leading culprit is a microscopic organism that lives in human feces.
Called cryptosporidium, it is a parasite transmitted in an egglike shell that can survive as long as 10 days even in chlorinated water. In 2007, the last year for which statistics are available, it was responsible for 31 recreational water outbreaks involving 3,726 people, according to the disease centers — up from 7 outbreaks and 567 people in 2004.
