We don't really know. If public and residential pools are properly maintained and chlorinated, the risk is thought to be low. Over the past 10 years, 150+ outbreaks have been reported, linking to small community pools and large water parks.

Many outbreaks go ignored because people do not think the pool water as a possible source of illness. It may take up to a number of weeks for some germs to cause symptoms of illness. The longer the time period between swimming and development of illness, the less likely people are to correlate their illness with swimming activity. As a result, the number of actual outbreaks is probably greater than those presently reported.