(CBS NEWS)-- Swimmers, be warned. A government study of public pools found widespread fecal contamination and the presence of other potentially dangerous parasites lurking amid the clear blue waters.
"Swimming is an excellent way to get the physical activity needed to stay healthy," said Michele Hlavsa, chief of the Healthy Swimming Program at the Centers for Disease Control and Prevention (CDC). "However, pool users should be aware of how to prevent infections while swimming. Remember, chlorine and other disinfectants don't kill germs instantly," she said.
CDC researchers collected water samples from filters at 160 public pools, booth indoor and outdoor, located in the metro-Atlanta area. They found "poop" in nearly 60 percent of the pools, with tests revealing 58 percent of the water samples were positive for the bacteria Escherichia coli, or E. coli.
E. coli is a bacteria that lives in the guts of people and animals and as such, indicates fecal contamination when it comes up in a test. The CDC pointed out, however, the pool samples did not test positive for E. coli O157:H7, the toxin-producing strain of the bacteria that can cause diarrhea and is sometimes the culprit behind foodborne disease outbreaks.
Dr. Susan Rehm, medical director at the National Foundation for Infectious Diseases and vice chair of dept of infectious diseases at Cleveland Clinic, said that people likely won't get sick from the mere presence of E. coli that doesn't produce toxins.
"E. coli is in drinking water," she pointed out to CBSNews.com.
However, she said other bacteria that does cause illness may be present.
The high percentage of E. coli contamination suggests some swimmers may be having a "fecal incident" in the water, the CDC said, or that some people simply aren't showering themselves thoroughly enough before they enter the pool.
E. coli was not the only microbe found via the tests. The CDC also found Cryptosporidium and Giardia, two parasites that are spread through feces and cause diarrhea, in less than 2 percent of samples. A mouthful of Cryptosporidium, known as "Crypto," is sufficient enough to cause an infection, which may lead to stomach cramps, dehydration, nausea, vomiting, fever and weight loss. Symptoms can come and go over the course of month, but people with weakened immune systems may develop fatal illness, according to the CDC.
Giardia can cause symptoms for one to two weeks, including diarrhea, gas, stomach or adominal cramps, "greasy stools" and dehydration, according to the health agency.
The researchers note their tests did not determine whether these germs were "alive," or able to cause infections.
Also present in some pool samples was the bacteria Pseudomonas aeruginosa, which can cause skin rashes -- sometimes called "hot tub rash" -- and ear infections. The bacteria was detected in 59 percent of samples tested. Pseudomonas could be introduced by swimmers, but may also be indicative of natural contamination.
The CDC's study did not look at private pools, water parks or other recreational water areas, however, the agency said it's unlikely that hygiene practices differ between those included in the study and those who swim elsewhere. In other words, pools outside the Atlanta area may be poopy too.
The study was part of the CDC's Recreational Water Illness and Injury Prevention Week, which will occur from May 20 to 26, to raise awareness for healthy swimming and ways to prevent so-called recreational water illnesses (RWIs). It was published May 16 in Morbidity and Mortality Weekly Report, the CDC's journal.
Other RWIs include, Legionella, Swimmer's Ear and wound infections, according to the CDC.
To reduce risks, the CDC recommends that all swimmers shower with soap before you start swimming and avoid the pool entirely when you have diarrhea.
"You really should stay out of the water for two weeks after" diarrhea, according to Rehm, because microscopic amounts of bacteria may still be present even after you feel better. She was not involved in the new research.
Take a bathroom break every 60 minutes -young children should especially, the CDC said -- and take a rinse shower before you get back into the water. Be sure to also wash your hands with soap and water after using the toilet or after changing baby diapers.
Pool owners should use pool test strips to make sure their chlorine and pH levels are maximized for germ-killing power. Proper chlorine should be 1 to 3 milligrams per liter, and pH should be between 7.2 and 7.8, the CDC said.
Said Hlavsa, "It's important for swimmers to protect themselves by not swallowing the water they swim in and to protect others by keeping feces and germs out of the pool by taking a pre-swim shower and not swimming when ill with diarrhea."
The CDC has more information on preventing illnesses at swimming pools.
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