Reviewed by Hansa D. Bhargava, MD on July 01, 2019
From the WebMD Archives

July 1, 2019 -- That crystal clear swimming pool looks so inviting as the thermometer climbs this summer. But the CDC is warning that danger lurks in many of America’s pools.

Outbreaks of diarrhea-causing cryptosporidium are increasing 13% each year, and 7,465 cases of crypto infection were reported from 2009 through 2017. The number of outbreaks reached 444, according to the agency’s report released last week.

But it’s not just crypto that swimmers have to be wary of. The CDC says 493 outbreaks of some kind of bacteria, parasite, or chemical between 2000 and 2014 were associated with recreational facilities, including pools, hot tubs, and playgrounds, and caused 27,219 cases and eight deaths. Most of those deaths were caused by bacteria or other pathogens, and 6% by chemicals.

Just last month, about 50 people were exposed to chlorine gas after a pump malfunctioned at a public swimming pool in Utah. The pump shot too much chlorine out of a jet in what local police called a “freak accident.”

Germs in the Pool

Of the outbreaks caused by bacteria and viruses, 58% were caused by cryptosporidium, which causes diarrhea that can last for up to 3 weeks. Thirteen percent were from pseudomonas, which causes hot tub rash and swimmer’s ear. Another 16% came from legionella, which causes Legionnaire’s disease and a milder illness with flu-like symptoms known as Pontiac fever.

Crypto is highly resistant to chlorine, which makes it hard to kill once it’s in the water.

“Swallowing just a mouthful of water with crypto in it can make otherwise healthy kids and adults sick for weeks with watery diarrhea, stomach cramps, nausea, and vomiting,” says Michele Hlavsa, chief of the CDC’s Healthy Swimming Program.

Every year, at least 15 to 20 outbreaks of diseases, like stomach bugs and diarrhea, are linked to swimming in public pools, according to the CDC.

A Clean Pool Doesn’t Smell

When entering a public pool, the scent of chlorine shouldn’t be a green light to jump right in. What you’re smelling isn’t clean water. It is, in fact, the opposite.

Mary Ostrowski, senior director of chlorine issues at the American Chemistry Council, says, “Properly treated swimming pools do not have a strong chemical odor. When chlorine in pool water combines with substances such as dirt, body oils, sweat, urine, and fecal matter from swimmers' bodies, chemical irritants called chloramine are produced. 

“It is chloramines in pool water, not chlorine, that give off that chemical odor and cause swimmers’ eyes to sting and redden,” Ostrowski says.

So that strong smell that hits your nose signifies that the pool’s water is dirty and should have its chlorine and pH levels tested. Once chloramines levels reach a point where you can smell them, they can irritate your eyes, skin, and nose.

Germs like crypto, E. coli, and giardia are spread in public pools where chlorine and pH levels are too low. Symptoms of all three illnesses include diarrhea, weight loss, nausea, vomiting, dehydration, and stomach cramps.

Keep the Pee Out of the Pool

There is also the problem of swimmers using pools as toilets. In 2017, researchers at the University of Alberta tested water at 31 swimming pools and hot tubs and found high levels of the artificial sweetener acesulfame potassium from each location. Their only conclusion? People were urinating in the pools and hot tubs and releasing the sweetener through their pee.

Urine alone is not the problem, but it mixes with chlorine and sweat to create toxic compounds, researchers say.

The answer to these problems isn’t pouring more chlorine in the water. Chlorine should be added in moderation or else it will harm the swimmers. Improperly chlorinated water puts swimmers at risk for dermatitis, skin infections, and rashes.

Saltwater pools, while refreshing, are not the answer to a “chemical free” alternative. Saltwater pools use chlorine, too.

Stay Safe This Summer

Here are some tips to protect you and your kids when the temperatures rise and the public pool is the only thing that will cool the heatwave:

  • Don’t swim or let your kids swim if sick with diarrhea.
  • Check the pool, hot tub, and water playground inspection scores.
  • Use test strips to check the water’s pH and chlorine levels. You can get free test kits from the website of the Water Quality & Health Council.
  • Try not to swallow the water.
  • Take small children on frequent bathroom breaks.
  • Shower before getting into a pool.
  • Listen for the sound of a working pool pump.
  • Change diapers in a diaper-changing area and away from the water.

Show Sources

Michele Hlavsa, chief, Healthy Swimming Program, CDC.

Mary Ostrowski, senior director of chlorine issues, American Chemistry Council.

NBC News: "'Freak accident' at Utah pool sickens dozens with chlorine gas." “Dozens of Utah public pool swimmers sickened by chlorine gas.”

CDC: “Outbreaks Associated with Treated Recreational Water — United States, 2000–2014,” “Cryptosporidiosis Outbreaks — United States, 2009–2017,” “Parasites - Cryptosporidium (also known as ‘Crypto’).”

Livescience: “Public Swimming Pools: How Dirty Are They?”

PBS: “What’s really in public swimming pools?”

ASCPublications: “Sweetened Swimming Pools and Hot Tubs.”

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