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Clear the Pool: Diarrhea Outbreaks Can Be Prevented

WebMD Health News

May 24, 2001 -- Swimmers, take note. Five diarrhea outbreaks reported to the CDC last summer were all linked to chlorinated swimming pools. In fact, reports of such outbreaks have increased in recent years, prompting the agency to issue advisories to pool operators and the general public.

The perpetrator -- a parasite called Cryptosporidium parvum -- "now accounts for 80% of the outbreaks we see," says Michael Beach, PhD, an epidemiologist with the CDC's National Center for Infectious Diseases.

While infections caused by the bacteria known as E. coli have been linked with poorly maintained chlorinated pools, Cryptosporidium has proven to be "virtually chlorine-resistant," says Beach. "It can survive for days in a chlorinated pool."

Infection with Cryptosporidium, called cryptosporidiosis, causes an acute watery diarrhea often associated with abdominal cramps. Less common symptoms include vomiting, fever, and loss of appetite. Symptoms usually persist for one to two weeks, but shedding of the bug in the stool may last for several weeks.

The CDC investigated two of last summer's outbreaks and reported their findings Thursday. The outbreaks occurred in Ohio and Nebraska and involved about 1,000 people.

A private swim club was linked to 700 cases in Delaware Country, Ohio and three neighboring counties. The outbreak began in late June and continued through September. Of over 250 stool samples tested, 70% were positive for Cryptosporidium. Researchers found that five fecal accidents -- one of which involved loose diarrheal stools -- had occurred during the time period.

Swimming in the pool -- and swallowing pool water (including under the pool sprinkler) -- greatly increased risk of developing the illness, the CDC report says.

The second outbreak investigated occurred in Douglas County, Neb. Initial cases were at one private swim club, but increased to include cases at another private swim club and at other local pools. Again, investigators detected this nasty bug. Fecal accidents had been observed at both private clubs that were involved.

Both outbreaks went unreported for several weeks, possibly because those who became ill did not see a doctor, the report says. During that time, the ill people continued to swim, increasing the likelihood that contamination of pools continued to occur.

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