Seeing diaper-clad infants in her neighborhood swimming pool without protective rubber pants led Karen Byers to search for a new place to take a dip.

She had good reason to be concerned. The Centers for Disease Control and Prevention (search) says more Americans — perhaps a thousand or more each year — are getting sick from public swimming pools.

That's not so many when you consider the millions of people who go swimming. However, reported pool-related outbreaks — mainly bouts of diarrhea — rose from two in 1986 to 21 in 2000, the most recent CDC statistics available. While the agency does not keep track of how many people were affected in those cases, it does know that most of the 16,800 confirmed illnesses in the 1990s linked to outbreaks in recreational waters occurred in swimming pools and spas.

"And that's only a fraction of what's out there," said Michael Beach, epidemiologist with the CDC's Division of Parasitic Diseases. "There are definitely a lot more cases that are not being reported. We believe some of the biggest outbreaks are in pools."

The latest numbers from the federal agency show that more than 1,800 pools had to be immediately closed after inspections found serious health violations that put swimmers at risk, such as not having enough disinfectant to kill germs in the water. The CDC analyzed 22,131 inspections conducted two years ago and found that 54 percent uncovered one or more pool safety violations, everything from filtration to chlorine problems.

"That's a shocking number for us to see — those are clearly violations that mean, 'Everybody out,"' Beach said.

Government health officials are urging pool operators and swimmers to do more to prevent the spread of disease. They are pressing for more regular inspections and better staff training — and encouraging swimmers to stay out of the pool when they have diarrhea.

"We need to do a better job of maintaining the pools and spas in this country," said Beach.

Another CDC study, released in July, said similar health violations forced the closing of one in nine public spas — those operated by hotels, apartment complexes, gyms or campgrounds — over a five-month period in 2002.

Improperly treated pools can be the source of a range of waterborne illnesses, including giardia, E. coli, shigella and cryptosporidium, said Joan Rose, a microbiologist at Michigan State University (search).

"Swimming clearly provides an opportunity for good physical activity — it's great fun," Beach said. "The CDC isn't trying to tell people to stop swimming. We are trying to raise awareness, help people understand what the issues are and swim responsibly."

One of the largest pool-related outbreaks in the country happened last August in Lawrence, Kan., when as many as 600 people may have been sickened by the parasitic disease cryptosporidium (search). The CDC found that the parasite was spread through local pools, day care centers and people who lived together.

This summer, the Lawrence-Douglas County health department has been trying to help pool operators and swimmers learn how to keep their pools germ-free. The No. 1 message: Don't swim if you have diarrhea.

"We know last year they had been swimming when they had diarrhea. That is really, really not something to do," said W. Kay Kent, health department director.

Twenty-six children became sick from an E. coli outbreak at a popular water park in Marietta, Ga., six years ago. State health officials determined the pool had been contaminated by human feces around one of the pool's slides.

The outbreak prompted stronger regulations for pool, lakes and other bathing facilities across Georgia. Now all public pools must show their inspection scores upon request.

Florida, the largest pool state in the Southeast with a million residential and commercial pools, faces many healthy swimming challenges. Hotel pools quickly fill up with tourists who aren't used to being around a swimming pool, said Wendy Parker, spokeswoman for the Florida Swimming Pool Association.

"We're dealing with a population who are enjoying themselves on vacation; they're not as worried about things as they might be if they're in their own back yard," Parker said. "It's a challenge to operate a pool and educate bathers."

Byers, who was disgusted with what she saw at her neighborhood pool, tried several other pools before settling with the one at Atlanta's Piedmont Park, about seven miles from her home.

She described it as cleaner and better maintained than other pools she visited.

"I'll keep coming back here — unless I see a bunch of babies in the pool," she says with a laugh.