The Sprayground at Seneca Lake State Park closed Aug. 15, and officials continue to investigate how cryptosporidium ended up in two storage tanks that supply water for the park near Geneva.
According to the Centers for Disease Control and Prevention, the last time a similar outbreak affected more people - nearly 5,500 - was in 1995 in Georgia. Contaminated drinking water in the Milwaukee area sickened more than 400,000 people in 1993.
"We recognize this is a significant outbreak and our priority is to continue working with counties to increase public awareness about the precautions everyone should take to stop further spread of illness," said state Health Department spokesman Jeffrey Hammond.
Dr. Andrew Doniger, Monroe County's health director, said more reported illnesses are coming from those who had contact with sick children. He said caregivers must wash their hands thoroughly and disinfect children's toys.
Cryptosporidiosis is very contagious and can cause symptoms including diarrhea, nausea, vomiting and fever. The disease usually goes away without treatment in healthy individuals. Food service workers experiencing symptoms should stay home, as should children in day care.
Geneva is 38 miles southeast of Rochester.