At least 32 outbreaks caused by Cryptosporidium linked to swimming pools or water playgrounds in the United States were reported in 2016, compared with only 16 reported outbreaks in 2014, according to preliminary data published in the CDC’s Morbidity and Mortality Weekly Report. The parasite can spread when people swallow something that has come into with the feces of a sick person, such as pool water contaminated with diarrhea.
While the number of reports has doubled, it remains unclear whether the number of outbreaks has increased or whether better surveillance and laboratory methods are leading to better outbreak detection, CDC researchers wrote in the reports.
According to the report, in 2016, Alabama, Arizona, Ohio, and other states investigated and controlled Crypto outbreaks linked to swimming pools or water playgrounds. Those outbreaks highlight the ongoing challenges that treated recreational water venues have with Crypto due to how difficult it is to kill and the small number of germs that can make people sick. Arizona identified 352 people sick with Crypto for July–October 2016, compared with no more than 62 cases for any one year in 2011–2015. Ohio identified 1,940 people sick with Crypto in 2016, compared with no more than 571 cases for any one year in 2012–2015.
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. Swallowing just a mouthful of water contaminated with Crypto can make otherwise healthy people sick for up to 3 weeks with watery diarrhea, stomach cramps, nausea, or vomiting, and can lead to dehydration.
CDC officials recommend closing pools and treating the water with high levels of chlorine when responding to a diarrheal incident in the water or an outbreak.
The best way to help protect yourself and patients from germs that cause diarrhea is to follow these steps:
- Don’t swim or let children swim if sick with diarrhea.
- 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.
The CDC's report on Cryptopsporidum started Healthy and Safe Swimming Week, which began today, May 22. CDC officials encourages swimmers to help protect themselves, family, and friends from Cryptosporidium and other germs in the water we swim in. For more information and other healthy and safe swimming steps, visit .
- Hlavsa MC, Roellig DM, Seabolt MH, et al. Using molecular characterization to support investigations of aquatic facility–associated outbreaks of cryptosporidiosis—Alabama, Arizona, and Ohio, 2016. MMWR Morb Mortal Wkly Rep. 2017;66:493–7.