Germs in the Swimming Pool: A Survival Guide

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Although jumping in the swimming pool is a great way to escape the heat and get some exercise, be aware there are plenty of disease-causing germs lurking below the water's surface.

Between 2015 and 2019 the Centers for Disease Control and Prevention (CDC) recorded 208 outbreaks of illness linked to swimming pools and hot tubs that resulted in 3,646 infections, 286

hospitalizations and 13 deaths, and experts say those numbers could be much higher.

Nearly all of the recorded outbreaks (96 percent) were associated with public pools, hot tubs or water playgrounds. Hotels and resorts accounted for 34 percent of outbreaks, with the

majority of them originating in hot tubs (70 percent) versus pools. And most outbreaks occurred in the months of June, July and August.

“With public pools, you have more people with more germs coming into that water,” said Michele Hlavsa, chief of the CDC’s Healthy Swimming Program. “So, they are more likely to have an

outbreak versus if it's just one family using the pool — they're bringing in less germs.”

Cryptosporidium: The leading cause of recreational water-related outbreaks originated from cryptosporidium (also known as crypto), a parasite that can cause a gastrointestinal illness such

as diarrhea, the CDC report found.

“Once [crypto] gets into the pool water and it's exposed to chlorine levels that you would expect to see in a well-operated pool, it can survive for more than seven days,” said Hlavsa, who

also coauthored the CDC report. If swallowed, the parasite can cause diarrhea that lasts more than three days — and this can be especially dangerous for older adults, she added.

Causes of Outbreaks​Cryptosporidium (parasite): 37 percentLegionella (bacterium): 31 percentE. coli (bacterium): 2 percentGiardia (parasite): 1 percent​Norovirus (virus): 1 percent​​

Source: CDC

Legionella: A bacterium called legionella was the next most common cause of outbreaks and the source of all 13 recorded deaths between 2015 and 2019. It can cause respiratory infections such

as a severe type of pneumonia, called Legionnaires’ disease, or a less serious illness called Pontiac fever, which can cause flu-like symptoms. People 50 and older, current or former

smokers and those with weakened immune systems are more likely to develop a lung infection from the bacteria, according to the CDC.

“When I think legionella, I think hot tubs,” Hlavsa said. “And when the hot tubs are jetting that air out, if there’s legionella in the hot tub, the droplets can be inhaled.”