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.
The CDC is advising pool operators to intensify their filtration and chlorination practices. Pool operators should also educate swimmers that anyone with diarrhea -- adults and children -- should not swim in pools while they are ill and for two weeks after diarrhea ceases, the report says.
"Swimming is a shared-water experience," says Beach. "If someone ill with diarrhea contaminates the water and you swallow the water, you're going to get infected."
Practicing better hygiene also helps, Beach tells WebMD. His advice:
- After using the restroom, wash your hands.
- Change baby diapers in a restroom diaper changing station -- not on the chaise lounge, picnic table, or alongside the pool. Wash your hands afterwards.
- Don't swallow pool water, even a little bit.
- Children and adults should not swim if they have diarrhea. Encourage children to take regular bathroom breaks when they're swimming to reduce the chance of fecal accidents.
"This parasite is very small in size, so it challenges even the best filtration system," Beach tells WebMD. "You don't need to swallow very many of them to get sick. It takes only one accident to spread infection to everyone in the pool, because [the bug] exists in very high quantities in diarrheal stools."
The CDC's goal "is not to scare people against swimming," he says. "It's a fantastic exercise activity. And most people don't get sick. The point is, we can do something about reducing the risk. Swim responsibly. It's in everyone's health interest to take care of this."
In some states, things are changing out there to make swimming pools, spas, and water parks cleaner.
In Georgia, only 30 counties currently follow the state's pool code, says Peter Conrady, aquatics coordinator with Cobb County, Ga. and chair of the Georgia Recreation and Parks Association's Aquatics Section. In recent years, an E. coli outbreak in one of that county's water parks created a big stir in local and national media.
But as of June 1, all of Georgia's counties will be following the same code, which has been revised based on guidelines set by the CDC and other agencies, Conrady tells WebMD. "We're making an effort to increase chlorine levels in pools and spas, creating awareness of maintaining those levels and testing the water more often." New personnel will be hired to check the state's water facilities on a regular basis.
In the city pools she oversees, "we've been performing hourly chemical checks -- of chlorine and pH levels to maintain a pool environment that is germ and parasite unfriendly," says Mary Miller, director of recreation and community services for the city of Decatur, Ga. "Some pools are just starting to do this, but we've been doing these checks for years now," she tells WebMD.
When fecal contamination occurs, "we immediately empty the pool, remove the waste from the pool, raise the chlorine level to three parts per million [one part/million is maintenance level]," says Miller. In fact, state regulations are being rewritten to raise pool maintenance levels to the higher number, she says.
Harder to enforce, but just as important: "A child has to be either in swim diapers, leak-proof swimsuits, or diapers with tight-fitting plastic pants," Miller says. "We sell swim diapers here, sell them at cost. We're not out to make money; we just want to protect our patrons."
The pool policy is also posted near the door, to keep the public informed and help staff reinforce the rules, she says.
But making kids take extra trips to the bathroom?
"That's a good idea," Miller says. "Our day camp kids always go before they get into the water. But we certainly can encourage all the kids to take bathroom breaks more often."