When you take your toddler to a swimming pool, you know that you're going have to stay alert at every moment to be sure that she's safe in the water. You might not realize, though, that there's another hazard that you should also keep in mind: the possibility that your child might get sick from germs in the pool water.

Wanda Stephens of Grayson, Ga., knows just how dangerous germs in pool water can be. In June 1996, her 4-year-old daughter spent two weeks fighting for her life when she developed hemolytic-uremic syndrome caused by E. coli infection. The doctors told Stephens that E. coli is usually spread by food – in particular, by undercooked hamburgers. However, Stephens' daughter hadn't eaten any hamburgers. Instead, she had been exposed to the dangerous disease at a swimming pool. A health department investigation showed that the chemical levels in the pool water hadn't been maintained properly. As a result, E. coli bacteria that had found their way into the water (probably from a person who was infected with E. coli but didn't know it) survived long enough to make a little girl very, very sick.

Fortunately, life-threatening illnesses associated with swimming pools are rare. But less serious illnesses are not. During the past 10 years, at least 15,000 people have become ill from swimming, according to the U.S. government's Centers for Disease Control and Prevention (CDC). Most of these illnesses were diarrheal illnesses, which were spread when people accidentally swallowed pool water that had been contaminated with fecal matter.

Because community pools are used by large numbers of people, outbreaks of waterborne diarrheal illness can be very large. In one outbreak involving a swim club pool in Ohio in 2000, more than 700 people became sick after the water was contaminated with the parasite Cryptosporidium. In an earlier outbreak in Wisconsin, swimmers from three different pools became sick after a single child who was infected with Cryptosporidium had "accidents" in each of the pools on three successive days.

The risk of waterborne illnesses isn't limited to traditional pools. Illnesses can also be spread in other settings in which people share water, such as hot tubs, spas and water park attractions. Several recent disease outbreaks have been traced to contaminated water in the fountain-style attractions that small children play in at water parks.

Chlorine Cautions
People often assume that they can't get sick from swimming in pools because chlorine kills all the germs in pool water. However, this assumption isn't completely correct. Although chlorine does kill germs, it has a couple of limitations.

First, if a pool's chlorine and pH levels aren't maintained properly, the chemical can't do its job. So it's crucial for pool personnel to test the water regularly and add chemicals when they're needed.

Second, chlorine takes time to work. It doesn't kill all germs instantly, and certain germs, such as Cryptosporidium, are relatively resistant to it. (E. coli, on the other hand, is very sensitive to chlorine and shouldn't survive for more than a minute or so in a well-maintained pool.) Chlorine alone can't keep a pool safe. Swimmers have to do their part, too, by practicing healthy swimming behaviors. Parents of toddlers have an especially important role to play here, because children of this age are especially likely to have "accidents" in the pool.

"If you're taking a child who is not potty-trained to a swimming facility, the child needs to wear a diaper covered by something else, such as rubber pants or the type of bathing suit that has a double waistband and elastic legs," says Melanie Sasse, recreation supervisor for the Montgomery County, Maryland Department of Recreation. At the 10 community pools run by Sasse's department, all toddlers are required to wear rubber pants or a similar covering over their diapers.

Taking older children to the bathroom frequently is also an important precaution. "Diaper-aged children aren't always the ones responsible for fecal accidents," Sasse says. "Sometimes, accidents happen to older kids who waited too long to go to the bathroom." Sasse points out that many swimming facilities have short "adult swim" periods every hour or so; this can be an ideal time for a bathroom break.

The CDC asks everyone to practice these six healthy swimming behaviors:

• Don't swim when you have diarrhea.
• Don't swallow pool water.
• Wash your hands with soap and water after using the toilet or changing diapers.
• Take your children on bathroom breaks often.
• Change diapers in a bathroom and not at poolside.
• Wash your child thoroughly (especially the rear end) with soap and water before swimming.

In addition to following these rules, parents may want to check to make sure that a pool is properly maintained. Stephens has been doing this ever since her daughter's illness. She gets to know the staff at every pool that her children swim in, and she even carries a pool water testing kit so that she can make sure that the pools are properly chlorinated.

"I would like other parents to know that pools and water parks can be a great source of fun, but also a source of illness as well," Stephens says. "It is crucial that parents be aware of how a pool is maintained and whether or not the chemicals are at the proper levels. Parents should stay involved and pressure pool maintenance staffs to keep up the pools properly."

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• Talk about it!