Outbreaks of a parasitic infection linked to swimming pools and water playgrounds are increasingly being reported to CDC, with twice as many outbreaks in 2016 as in 2014.

At least 32 outbreaks caused by Cryptosporidium, or Crypto linked to swimming pools or water playgrounds in the United States were reported in 2016, compared with 16 outbreaks in 2014, according to preliminary data published today in CDC’s Morbidity and Mortality Weekly Report. The parasite can spread when people swallow something that has come into contact with the feces (poop) of a sick person, such as pool water contaminated with diarrhea.

In comparison, 20 Crypto outbreaks linked to swimming were reported in 2011, 16 in 2012, and 13 in 2013. It is not clear whether the number of outbreaks has increased or whether better surveillance and laboratory methods are leading to better outbreak detection.


Crypto is the most common cause of diarrheal illness and outbreaks linked to swimming pools or water playgrounds because it is not easily killed by chlorine and can survive up to 10 days in properly treated water.

Standard levels of chlorine and other pool disinfectants kill most germs within a few minutes. However, Crypto is extremely hard to kill at standard levels of pool disinfectants.

Swallowing just a mouthful of water contaminated with Crypto can make otherwise healthy people sick for up to three weeks with watery diarrhea, stomach cramps, nausea, or vomiting, and can lead to dehydration.

“To help protect your family and friends from Crypto and other diarrhea-causing germs, do not swim or let your kids swim if sick with diarrhea,” said Michele Hlavsa, R.N., M.P.H., chief of CDC’s Healthy Swimming Program. “Protect yourself from getting sick by not swallowing the water in which you swim.”

Ohio is one example of a large increase in Crypto. 1,940 people were sickened with Crypto in 2016, with more than 1000 cases reported in three Central Ohio counties. This compares with no more than 571 cases for any one year in 2012–2015.

The best way to help protect yourself and others from germs that cause diarrhea is to follow these steps:

·         Don’t swim or let your kids swim if sick with diarrhea.

o   If diarrhea is caused by Crypto, wait until two weeks after diarrhea has stopped to go swimming.

·         Don’t swallow the water in which you swim.

·         Rinse off in the shower before getting in the water to help remove any germs on your body that could contaminate the water.

·         Take kids on bathroom breaks often, and check diapers in a diaper-changing area and not right next to the pool.

CDC recommends closing pools and treating the water with high levels of chlorine, called hyperchlorination, when responding to a diarrheal incident in the water or a Crypto outbreak.