Talk about a false sense of confidence in public health measures that are supposed to prevent disease, and almost nothing tops the misplaced faith that people have in chlorinated swimming pool water these hot summer days.
Chlorine in the right amount does kill germs that get into the water from swimmers' bodies. But it takes time, according to the U. S. Centers for Disease Control and Prevention (CDC).
People who swallow swimming pool water while the killing is underway, could catch what CDC terms "recreational water illness" (RWI). Most RWI involves diarrhea, vomiting, cramps, and other symptoms similar to food poisoning. Swimming in water contaminated with disease-causing microbes can also cause infections in the eyes, nose, ears, and in cuts and scrapes.
Most healthy children and adults recover quickly from RWI. However, it can put some high-risk people in the hospital.
Among them are young children, older people already ill with chronic diseases, and individuals taking medicines that suppress the immune system. They include organ transplant recipients, and people taking medicine for infection with the AIDS virus, cancer chemotherapy, and certain drugs for severe arthritis.
CDC is campaigning this summer the inform pool operators, swimmers, and parents of young children about RWI.
Most RWI in swimming pools occurs because fecal material, which is loaded with bacteria, gets into the water. Young children can deposit hundreds of millions of disease causing bacteria when they go to the bathroom in the pool, or when their diapers leak. Children already ill with diarrhea pose a particular threat to other bathers.
Other children and adults make their contribution, as well. CDC says that tiny amounts of fecal material rinse off all swimmers' bottoms and get into pool water.
The agency is urging parents of young children to wash their kids' rear ends with soap and water before letting them into the pool. Adults should heed the "Please Shower Before Swimming" signs, CDC says, and realize exactly what part of the body most needs to be washed.
People with diarrhea should not swim at all because of the risk of infecting others, CDC says. Parents should take kids on frequent bathroom breaks. Diaper changes should be done in a bathroom, and not at poolside. Everyone should avoid swallowing and inhaling pool water.
Chlorinated water is no reason to ignore that advice, even in the best-maintained swimming pools where staff is constantly sampling the water.
Studies show that chlorine kills most bacteria, including the notorious E. coli germs that cause many cases of RWI diarrhea, in less than one minute. However, chlorine needs more time to kill other disease-causing microbes.
The hepatitis A virus, for instance, can survive for about 16 minutes in properly chlorinated pool water. A parasite called Giardia, one of the most common causes of water-borne disease, can survive for about 45 minutes. Cryptosporidium, which causes severe gastrointestinal illness, can live in chlorinated pool water for more than 6 days.