Crypto in swimming pools: Swimmers’ diarrhea caused by a parasite that chlorine doesn’t kill.

The Nasty Parasite That Lives in Chlorinated Swimming Pools

The Nasty Parasite That Lives in Chlorinated Swimming Pools

Health and medicine explained.
July 2 2015 1:38 AM

Don’t Go in the Water

Why a nasty parasite is thriving in chlorinated swimming pools and water parks.

Baby learning how to swim in swimming pool
Beware that baby’s bottom.

Photo by Photobac/Shutterstock

If you’re in the pool this summer when some adorable toddler has an “accidental fecal release,” you’d better hope it’s a Baby Ruth rather than soft serve. Because as disgusting as it is to be swimming with a formed stool—it’s much worse to be swimming in diarrhea. For one thing, diarrhea goes everywhere. For another, diarrhea’s full of the germs that caused it.

And for a third, the pool’s chlorine might not kill those germs—especially if that toddler’s diarrhea was caused by a microscopic parasite nicknamed “Crypto.”

Officials at the Centers for Disease Control and Prevention and local health departments have been grappling with increasing outbreaks of swimmer’s diarrhea caused by Cryptosporidium. Crypto cases have more than doubled since 2004, with 8,008 known cases in 2012. When we think of swimming and infections, we usually think about ear infections or rashes from slimy hot tubs. And it’s this ignorance of Crypto that, ultimately, is helping Crypto spread.

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Until 1976, veterinarians knew more about Crypto than most doctors did. That’s because the parasite causes diarrhea in baby cows. Its cows-only reputation changed when a 3-year-old from Tennessee and an immunocompromised man were diagnosed with Crypto. In immunocompromised people, Crypto morphs from a weeklong bout of watery diarrhea into profuse, chronic diarrhea and even life-threatening wasting. Despite two small outbreaks from drinking and swimming water in the 1980s, most public health officials still thought of Crypto as a disease of the immunocompromised. It was particularly prevalent in people infected with HIV. By 1992, almost 1 of every 25 AIDS patients in Los Angeles were infected with Crypto. But Crypto’s reputation and victims were about to change.

In 1993, Crypto made its big public health splash when it broke out in Milwaukee. Half the city was ultimately infected—almost 403,000 people. But local health officials like Paul Biedrzycki, currently director of disease control and environmental health for Milwaukee, only learned about all this diarrhea when a doctor told them about a patient with cryptosporidiosis. “That’s weird,” Biedrzycki thought at the time. The patient had a healthy immune system, not AIDS.

When Biedrzycki and other officials looked closer, they found that local businesses had skyrocketing absentee rates and that Milwaukee retailers were running out of Imodium. It took several weeks to hunt down the source of Crypto: the public drinking water system.

But how did Crypto get into Milwaukee’s water in the first place?

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They’re still not sure, Biedrzycki says. But his best guess is that Milwaukee, which sits at the nexus of three rivers emptying into Lake Michigan, was hit with dirty runoff from upstream farms and neighborhoods. The dirty water poured into Lake Michigan and got sucked into the public water treatment plant and overwhelmed its defenses.

While he can’t pinpoint the original source of Crypto, Biedrzycki is sure about one thing. “It wasn’t because we were incompetent,” he says. The treatment plant was in full compliance with the Safe Drinking Water Act. When the plant sucked up dirty Lake Michigan water, it pulled out the big pieces of dirt, filtered out the little pieces, and then chlorinated everything that was left. A process that works against most germs—but not Crypto.

Unlike bacteria such as E. coli or parasites such as Giardia, Crypto can live for days in chlorinated water. It lurks in a protected form called an oocyst. When a swimmer swallows the oocyst, the parasite pops out and squirms into the cells lining his or her gut, where it multiplies. These new parasites then ride out the swimmer’s other end, with up to 100 million oocysts coming out in every fecal release.

In 1997, 73 people came down with diarrhea from Crypto after playing at a sprinkler fountain in Minnesota; two years later, 38 got sick from Crypto and another bacteria after visiting a badly maintained splash fountain in Florida. In 2000, more than 200 swimmers in Ohio and Nebraska got sick. In 2005, more than 1,700 were infected with Crypto after playing at a New York spray park—a massive outbreak that led to a class-action lawsuit. Then in 2007, Utah suffered an outbreak of at least 1,900 cases, prompting officials to ban kids younger than 5 from public pools.

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So what’s behind the increase in outbreaks?

For one thing, pool operators don’t often have the tools they need. Pools rely on chlorine to kill most germs, and it’s expensive and difficult to retrofit pools so their systems irradiate or add ozone to the water—methods that actually kill Crypto and are used nowadays by drinking water treatment plants.

For another, not every operator even knows how to maintain a pool or handle an accidental fecal release. Only about half the states require public pool operators to take two-day training and certification courses, says Tom Lachocki, CEO of the nonprofit National Swimming Pool Foundation. This lack of training and regulation shows: In 2008, the CDC found that 1 in 8 swimming pools had public health violations.

But it’s not just pool operators’ ignorance or the lack of oversight that’s driving these outbreaks. It’s the ignorance of us 61 million American swimmers. Ignorance and some, well, improper behavior.

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“It’s about common courtesy,” says Michael Beach, associate director for healthy water at the CDC. “You swim in the pool. You pee and poop in the restrooms.” Especially kids. Kiddie pools, Beach says, are a major source of outbreaks. Not that we grown-ups are off the hook; the average American adult carries .14 grams of poop—about a third the weight of a Tic Tac—around their anus. Meaning it’s not just kids who are spreading Crypto.

But our ignorance ultimately gives the CDC hope: hope that by spreading information the agency can stop Crypto from spreading in chlorinated pools. The “key is raising people’s awareness,” says Beach, that pool water isn’t sterile, and you shouldn’t swim when you’re ill. Awareness that you should shower your kids and yourself before swimming. And awareness that you should take your kids out of the pool hourly for bathroom breaks. “If you’re ill with diarrhea,” says Beach, “you have no business in a swimming pool. Find a different activity.”

In other words, get that adorable toddler with diarrhea out of the pool, and take the kid someplace where an accidental fecal release won’t wreak havoc on public health.