Why Swimming Pools Can Make You Sick

Can't wait to dive into that swimming pool? Well, here's a reason to hold your breath. That water could be teeming with germs waiting to get you sick.

More than 4,000 people were sickened by a recreational water illness between 2005 and 2006 alone, according to the Centers for Disease Control and Prevention

"The assumption that swimming pools are cess pools can be correct," Dr. Ranit Mishori, assistant professor of family medicine at Georgetown University Medical Center, told AOL Health. "Swimming is a wonderful activity, but everyone should take precautions."

The problem is you're sharing germs with everyone else in the pool, and they can be transmitted as easily as swallowing a mouthful of water while playing Marco Polo.

A well-maintained swimming pool uses the appropriate amount of chlorine and other disinfectants to kill bacteria which cause illness, explained Dr. Philip J. Tierno Jr., director of clinical microbiology and immunology at NYU Langone Medical Center in New York City. However, the time it takes chlorine to kill each germ varies. And the more crowded the pool, the faster the chlorine is used up. Although diarrhea is by far the most commonly reported, swimming-related illnesses can also manifest as eye, ear, respiratory, skin or neurologic infections.

"All it takes is one child with diarrhea, or whose diaper falls off, to contaminate a whole pool," said Mishori.

Feces, even a miniscule amount, "is by far the biggest health hazard in swimming pools," agreed Tierno.

Here are the pathogens you might be sharing the pool with this summer:

Cryptospordium: This chlorine-resistant parasite is the leading cause of gastroenteritis outbreaks at swimming pools, and can live for days in even properly chlorinated pools, according to the CDC.

Giardia: Like crypto, giardia is a microscopic parasite passed through feces, which can cause diarrhea.

Noroviruses: Exposure to this group of viruses can cause vomiting, nausea, stomach cramping and diarrhea that can last for several days.

Pseudomonas aeruginosa: This germ -- which is present in soil and water, not feces -- is responsible for "swimmers ear," an itchy or painful inflammation of the ear.

Unlike flu viruses, new strains of swimming pool microorganisms don't premiere each summer. "We've seen these same strains for years," said Tierno.

And because they aren't going away any time soon, the best way to stay safe is by practicing good personal hygiene.

Shower with soap before entering the pool. Don't swallow pool water, spit into the pool, or blow your nose into the water.

Children's swim diapers should be secured tightly and changed frequently, preferably not poolside. Anyone with diarrhea should skip the pool altogether.

Also, be on the lookout for lifeguards or facility managers running pH tests to make sure chlorine in the water is at an optimal level. Clear water and clean, not slimy, tiles are also good signs.

If the pool is standing room only on a hot day, reconsider getting in, since your risk of getting sick will be higher.

Very young children, pregnant women and people with immune deficiencies who may be more susceptible to illness, should limit the time spent in a pool.

"No one should avoid going to the pool altogether," noted Mishori. "Just be safe."