Parasites, bacteria in U.S. pools made thousands of people sick, CDC says

Dirty water in pools, hot tubs and water playgrounds made more than 27,000 people sick across the U.S. between 2000-2014, according to a new report from the Centers for Disease Control. Eight people died as a result.

The report, released Friday, found that pools and other “treated recreational water” were linked to 493 outbreaks of disease over that period. Hotel pools were the top culprit, accounting for 32 per cent of the outbreaks.

“We weren’t surprised by the numbers,” said study author Michele Hlavsa, chief of the CDC’s healthy swimming program. “We hear about these outbreaks every summer.”

Some outbreaks are clearly linked to improper pool maintenance, she said. If a pool is kept at the CDC-recommended chlorine levels, it should kill most germs. “When we hear of an outbreak caused by an E. coli or a norovirus, we know that there’s something wrong with pool operation.”

But chlorine doesn’t kill everything.

The top source of outbreaks was a protozoa called Cryptosporidium, which can survive in a pool with normal levels of chlorine for up to seven days.

“They cause diarrhea, they cause cramps, and it’s usually gone after a week unless you’re immunocompromised,” said Jason Tetro, author and visiting professor at the University of Guelph.

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It gets in the pool, unfortunately, through poop. An infected person has diarrhea in the pool, or gets in the pool right after an episode, and the bug gets into the water. When someone swallows the contaminated water, they can get ill.

“Someone goes swimming, they have a diarrheal incident in the water, and other swimmers drink that water,” Hlavsa said.

Share this on X Click to share quote on X: "Someone goes swimming, they have a diarrheal incident in the water, and other swimmers drink that water," Hlavsa said.

Legionella bacteria, which can cause Legionnaire’s disease and pneumonia, is killed by pool chlorine, but seems to be more of a danger in hot tubs, said Hlavsa. This is because people get infected by inhaling water droplets. “It’s about those hot tub jets aerosolizing the water.”

They’ve even seen cases where people who weren’t in the water, but just near the hot tub, caught Legionella by inhaling the steam.

Another bacteria linked to outbreaks causes an ear infection called “swimmer’s ear” and “hot tub rash” — a rash that’s often shaped like the bathing suit you were wearing, because the fabric holds the dirty water against your skin.

People bring all kinds of things into the pool, Tetro said.

“Any time a body goes into water, there is going to be shedding,” he said.

“Water has this intrinsic ability to be able to get into crevices and then come out of crevices. So if you’re not paying attention to your hygiene, there’s definitely going to be fecal matter in the pool.”

Share this on X Click to share quote on X: "Water has this intrinsic ability to be able to get into crevices and then come out of crevices. So if you're not paying attention to your hygiene, there's definitely going to be fecal matter in the pool."

“A swimming pool really is a petri plate. If you don’t have a high enough chlorine concentration in there, then there’s a good likelihood that they’re going to grow.”

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How to protect yourself

Despite this, both Tetro and Hlavsa say they plan to continue to swim in public pools. It’s worth noting that 27,000 sick people is a tiny fraction of a per cent of the total U.S. population.

Here are some of their tips for safe swimming:

• Don’t swim or let your kids swim if they’re sick with diarrhea
• Shower before you get in, paying extra attention to the “crevices” that Tetro mentioned
• Shower when you get out, making sure to carefully wash your hands and face
• Check the pool’s inspection results if you can. Many municipalities make this information available online, or you can ask the pool administration.
• Consider bringing test strips with you to test the water before going in, to check if the chlorine is at the right level, suggests Hlavsa.
• Most importantly — don’t drink the water.

The CDC offers more safe swimming tips on their website.