The number of cases of Cryptosporidium in central Ohio topped 600 this week, following the holiday weekend and the unofficial end of summer and swimming pool season. Cases of cryptosporidiosis in Franklin and Delaware counties had reached 511 as of 2 Sep 2016, according to Franklin County Public Health.

Health officials had reached out to pool operators, physicians, schools and day-care centers about the outbreak. Many local pools have been “hyper-chlorinated” to flush out traces of the disease before the pools closed for the season.

Health officials say people who are sick should stay home from school or day care and avoid pools and water parks, where cryptosporidiosis and other diseases easily pass from person to person. An infected person can spread the disease long after diarrhea subsides and should avoid swimming for at least 2 weeks.