Exposure to crypto in pools and water playgrounds caused 4,232 illnesses between 2009-2017. The parasite is typically spread by people, children in particular, who swim too soon after having a case of diarrhea. Leading causes include swallowing contaminated water in hot tubs, pools or water parks, contact with infected cattle, and contact with infected persons in child care settings, according to the CDC.

Image of microscopic parasite Cryptosporidium

Unlike most germs that are killed within minutes by disinfectants like chlorine or bromine, Crypto can survive in chlorinated water for more than a week. And when someone gets sick, they can suffer with diarrhea for up to three weeks.

In addition to watery diarrhea, common symptoms of Crypto include stomach cramps or pain, dehydration, nausea, vomiting, fever and weight loss.

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For some with weakened immune systems, Crypto may lead to life-threatening malnutrition and wasting.

"We want people to go to pools and have a happy, good time," Michele Hlavsa, chief of the CDC's Healthy Swimming Program, told The AJC in May. "We just want to make sure people are doing it in a safe, healthy way."

Even a single mouthful of contaminated water can lead to a Crypto illness, she said.

To prevent Crypto, the CDC recommends practicing good hygiene, following local drinking water advisories and preventing contact and contamination with feces during sex.

More tips at cdc.gov.