With public pools opening up for the summer season, the time has come once again for the Centers for Disease Control and Prevention to issue its yearly plea: Please, if you have diarrhea or aren’t feeling well, don’t go swimming.

According to the CDC’s most recent Morbidity and Mortality Weekly Report, outbreaks of Cryptosporidium — a parasite that can spread when people swallow pool water contaminated with feces — are on the rise, with twice as many outbreaks in 2016 as in 2014.

There were at at least 32 outbreaks of Crypto linked to swimming pools or water playgrounds in 2016, and only 16 in 2014. In 2011, there were 20 Crypto outbreaks, 16 in 2012, and 13 in 2013. What isn’t clear is whether outbreaks have actually increased, or whether better surveillance and lab methods are leading to better outbreak detection.

Crypto is especially tough to get rid of because it isn’t killed easily by chlorine. That, and it can survive up to 10 days even in properly treated water.

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

There are some very easy steps you can take to prevent this from ruining your summer vacation, but everyone has to pitch in. Here’s what the CDC recommends:

• Don’t swim or let your kids 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 the swimming pool or hot tub.
• 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.

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