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A Fecal Parasite Is Causing More Disease Outbreaks, and Swimming Pools May Be to Blame, CDC Says

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A recent announcement from the U.S. Centers for Disease Control and Prevention (CDC) may put a damper on summer fun. A fecal parasite often spread by swimming is causing an increasing number of illness outbreaks, the agency says.

The number of disease outbreaks involving the parasite Cryptosporidium, also known as Crypto, increased by about 13% each year from 2009 to 2017, according to a new report from the CDC. People can become ill with cryptosporidiosis after exposure to contaminated human or animal fecal matter, developing symptoms including nausea, cramps and diarrhea that can last weeks and lead to serious malnutrition and dehydration.

Crypto outbreaks are still fairly uncommon in U.S. states and Puerto Rico: 444 were reported from 2009 to 2017, resulting in about 7,500 illnesses, almost 300 hospitalizations and one death. In the U.S., more than half of all recent Crypto-related illnesses could be traced back to swimming pools, water playgrounds and other treated-water recreation areas, since people may swallow contaminated water in these places. As such, infections are most common in July and August, the CDC says. (Untreated swimming waters, such as lakes and rivers, may also be a breeding ground for bacteria that cause illnesses such as E. coli, norovirus and Shigella, the CDC warned last summer.)

Other Crypto outbreaks have been traced back to cattle farms, childcare centers and consumption of unpasteurized milk and apple cider, according to the CDC.

With known outbreaks on the rise—and even more likely going unreported—the CDC emphasizes that no one should swim or allow kids to swim if they are sick with diarrhea. Swimmers should also take care not to swallow water, the CDC says. In addition, sick children should be kept home from school or childcare; people who are in contact with animals should wash their hands, clothes and shoes often; and people shouldn’t drink unpasteurized milk or apple cider.

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Write to Jamie Ducharme at jamie.ducharme@time.com