Diving into a public pool this summer? You might be plunging into a petri dish.
While chlorine is the go-to germ killer, it doesn’t work instantly. Some nasty germs can survive in treated water for minutes or even days, turning a refreshing swim into a risky dip.
And the threat is growing. Outbreaks of waterborne illnesses tied to pools and other recreational venues are on the rise — especially those caused by a resilient parasite that’s waiting to crash your summer plans with a case of watery diarrhea.
Not-so-crystal-clear
That sparkling blue water isn’t always as clean as it looks.
Every time someone jumps in, they bring more than just sunscreen and swimsuits, leaving behind germs, grime and bodily fluids that can make others sick.
According to the CDC, the average swimmer introduces:
- 8 million microbes in a single drop of spit
- 140 billion microbes from feces
- Up to two cans’ worth of sweat
- A full cup of urine
All of those substances mix with chlorine to form chloramines, a chemical byproduct that can irritate your eyes and lungs and give off that strong “pool smell” most people wrongly associate with cleanliness.
“It is a common myth that a strong chlorine smell is a good sign of a clean pool,” Lisa Cuchara, an immunologist and infectious disease specialist, wrote in The Conversation.
“In fact, it may actually be a red flag that means the opposite — that the water is contaminated and should perhaps be avoided,” she continued.
What’s really lurking in the water
Most pool-related illnesses happen when swimmers swallow contaminated water or come into contact with it through their skin.
If its levels are properly maintained, chlorine can kill many germs, like E. coli, in under a minute. Some germs, however, are far more stubborn.
Take hepatitis A. It can survive in a chlorinated pool for about 16 minutes. The virus usually gets in the water through fecal contamination, like if if someone uses the bathroom and doesn’t wash their hands before hopping back in.
Once infected, the virus can inflame the liver and disrupt its ability to function properly.
Then there’s giardia, a parasite that often enters pools when people have accidents in the water or don’t rinse off properly. It can take 45 minutes or longer to kill with chlorine, and just a small sip of contaminated water can trigger diarrhea, stomach pain, gas and nausea.
Super pooper parasite
Perhaps the worst offender is cryptosporidium, a microscopic germ with a tough outer shell that enables it survive in chlorine-treated water for up to 10 days.
Like giardia, cryptosporidium commonly spreads when someone with diarrhea contaminates the water and another swimmer swallows it.
Between 2009 and 2017, crypto caused nearly 450 outbreaks across 40 states and Puerto Rico, sickening more than 7,400 people, according to the CDC.
Outbreaks jumped 13% each year, with most traced back to people swallowing water from treated pools.
“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,” Michele Hlavsa, chief of CDC’s Healthy Swimming Program, said in a statement.
Bacteria, viruses and fungi, oh my!
Other troublemakers — including Shigella, norovirus and adenovirus — can also lurk in chlorinated water and wreck your gut.
Bacteria like Legionella and Pseudomonas pose additional risks. Legionella can cause a serious form of pneumonia, while Pseudomonas is known for triggering skin rashes and ear infections.
Even fungi get in on the act. Pool decks, ladders, and locker rooms are breeding grounds for fungal spores. Once established, they’re hard to eliminate and often resistant to regular cleaning.
That’s how infections like athlete’s foot — and other skin irritations — spread so easily in damp, high-traffic areas like your local community pool.
But don’t toss your trunks just yet
There are simple steps you can take to reduce the spread of viruses, bacteria and other germs in swimming pools.
- The CDC recommends staying out of the water if you have diarrhea and waiting at least two weeks after symptoms clear up to take a dip.
- Before you dive in, shower for at least a minute to rinse off dirt, sweat and any lingering germs.
- Parents should take kids on regular bathroom breaks and check diapers every hour — and never change them poolside.
- While in the pool, try not to swallow water. When you’re out, dry your ears well with a towel to help prevent swimmer’s ear.
- And, of course, don’t pee or poop in the pool. Sounds obvious? Not for everyone.
Last year alone, New York City’s parks department had to shut down pools 203 times to clean up after someone defecated, according to data obtained by The Gothamist.
That’s 44 out of 52 public pools closed at least once for a “code brown.” On one day in August, 12 pools were shuttered because of poop in the water.
Pee’s no better. In a national survey released last month, more than half of participants admitted to urinating in the pool as an adult.
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