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Hundreds of disease outbreaks over 15 years linked to pathogens in public pools

Pathogens tend to flourish in warm water.
Photo by NeONBRAND on Unsplash
Pathogens tend to flourish in warm water.

Here’s a fact that will certainly make you hesitate before jumping into a public swimming pool, hot tub or waterpark this summer: Disease-causing bacteria and parasites — often the result of people swimming with diarrhea — can be lurking in the water of those recreational facilities, even if the water has been properly treated.

Indeed, the Centers for Disease Control and Prevention (CDC) reported last Friday that public health officials in 46 states and Puerto Rico recorded 493 confirmed outbreaks of diseases associated with treated recreational water from 2000 through 2014. Those outbreaks caused at least 27,219 people to become ill and eight people to die. 

About a third (157) of the outbreaks were traced back to pools or hot tubs at hotels, motels, inns and lodges.

Less surprising was the finding that about half of the outbreaks started during the summer months of June, July and August. Not only are more pools open during the summer months, pathogens also tend to flourish in warm water. 

Leading causes

Public health officials were able to identify the source of 363 of the outbreaks that occurred during the 15-year period reviewed by the CDC researchers. Most of those outbreaks — 94 percent — were caused by pathogens, while the remaining ones were caused by chemicals.

The leading pathogen behind the outbreaks was Cryptosporidium, or Crypto, a parasite that causes watery diarrhea, stomach cramps, vomiting and other gastrointestinal problems.  It was responsible for 212 (58 percent) of the outbreaks in the report and more than 21,700 (89 percent) of the illnesses. Crypto spreads in pools when people swim while they have diarrhea. Other swimmers can then pick up the parasite by swallowing contaminated water. 

Legionella, a bacterium that causes the serious type of pneumonia known as Legionnaires’ disease as well as the less-severe Pontiac fever, was behind 57 outbreaks and 624 illnesses in the report. It was also responsible for at least six of the eight deaths, the CDC says. Hot tubs and spas are particularly good breeding grounds for legionella, and you don’t have to be in the water to become infected. You can breathe in the bacteria through contaminated water droplets while standing nearby.

Pseudomonas caused 47 outbreaks and 920 illnesses. It’s a type of bacteria that can result in swimmer’s ear and a skin condition known as “hot tub rash,” as well as pneumonia and other serious infections in people with weakened immune systems.

Don't swim with diarrhea

As the CDC points out, some pathogens — particularly Crypto — can survive in recreational water even when the facilities are chlorinated and properly maintained.  

“Chlorine cannot kill Crypto quickly,” said Michele Hlavsa, chief of the CDC’s Healthy Swimming Program, in a released statement. “We need to keep it out of the water in the first place. Don’t go into the water, and don’t let your kids go into the water, if sick with diarrhea.”

In fact, anyone — adult or child — with diarrhea should wait a full two weeks until after the diarrhea has stopped to go swimming, according to health officials.

Here are some other steps the CDC recommends you take to protect yourself and your loved ones from disease-causing pathogens in recreational pools:

  • Check the pools, hot tubs and water playground inspection scores. [These scores should be posted online or near the facilities themselves.]
  • Before getting in the water, use a test strip from your local retailer or pool supply store to check if the water’s pH and bromine or free chlorine level are correct. [This seems like a significant burden to place on consumers, but the CDC is recommending it.]
  • Don’t swallow the water. 
  • Take kids on bathroom breaks hourly, and change diapers in a diaper-changing area and away from the water.

The Minnesota Department of Health (MDH) also offers this advice: “If a pool has water that looks unclean, or unsafe, you should not swim in it. If you suspect that a pool does not meet public pool water standards and could possibly cause a waterborne illness, please report the pool by contacting MDH or the responsible agency.”

FMI: The CDC report was published in the agency’s Morbidity and Mortality Weekly Report (MMWR), where it can be read in full. For more information about waterborne illnesses, including outbreaks in Minnesota, go to the MDH website.

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