There's poop in public pools, according to a new report.

Researchers at the Centers for Disease Control and Prevention (CDC) found genetic material from E. coli bacteria in 58 percent of public pools they tested during the summer of 2012.

This shows that "swimmers frequently introduced fecal material into pools," which could spread germs to other people, the researchers wrote in their report. E. coli bacteria are normally found in the human gut and feces.

They also found genetic material from bacteria called Pseudomonas aeruginosa, whichcan cause skin rashes and ear infections, in 59 percent of pools.

The fecal material in pools comes from swimmers not showering before getting into the water, and from incidents of defecation in pools, according to the report. The average person has 0.14 grams of fecal material on their "perianal surface" that can rinse into a pool if a person doesn't shower first, according to the report.

The Pseudomonas aeruginosabacteria in the pools may have come from the natural environment, or from swimmers, the researchers said.

There were no samples that showed E. coli O157:H7, a toxin-producing E. coli strain that causes illness.

Two parasites, Cryptosporidium and Giardia, which also spread through feces and cause diarrhea, were found in less than 2 percent of samples.

The study included 161 pools in the Atlanta area, and the researchers noted their findings may not apply to all pools, but said there is no reason to think that contamination or swimmer hygiene practices differ between pools in the study and those in the rest of the country. The researchers collected samples of water from the pools' filters, and looked for the genetic material of specific bacteria.

"Chlorine and other disinfectants don’t kill germs instantly," said Michele Hlavsa, chief of CDC’s Healthy Swimming Program. It’s important that swimmers shower before getting in a pool, not swallow the water they swim in, and avoid swimming when they have diarrhea, she said.

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The CDC also recommends that parents of young children take children on a bathroom break every hour, or check diapers every 30 to 60 minutes. Diapers should be changed in a diaper-changing area, not near the poolside, the CDC says.

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