By Anne Harding

NEW YORK (Reuters Health) - Children age 10 and younger are more likely than older kids and adults to be sickened by swimming in bacteria-contaminated water, researchers from the Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention report.

Experts had long suggested that children might be at greater risk of swimming-related illness than adults, Dr. Timothy J. Wade of the EPA's National Health and Environmental Effects Research Laboratory in Chapel Hill, North Carolina, and colleagues note, but this is the first research to show that this is actually the case.

Wade and his team also found that an experimental method for gauging water quality by checking for bacterial DNA was not only quicker than the standard technique, but better able to predict pollution-associated health risks.

"Overall the current guidelines are protecting public health, but this probably has the potential to do better," Wade told Reuters Health. "Results can be obtained much faster and therefore an action could be taken much faster."

He and his colleagues compared water contamination levels and illness risk among visitors to three beaches on Lake Michigan and one on Lake Erie in 2003 and 2004.

Currently, local authorities will typically test beach water quality by trying to grow certain types of bacteria from water samples, which can take 24 to 48 hours to yield results. The newer method called quantitative polymerase chain reaction (QPCR) may be able to reveal contamination levels in as little as two hours.

To determine how well testing methods were able to gauge illness risk, the researchers tested water quality. Ten to 12 days later they interviewed people who had been visiting the beach on that day to see if anyone had gotten sick. Their analysis covered 78 days and included 1,359 water samples and 21,105 interviews.

On about one-third of the days, levels of Enterococcus bacteria in the water exceeded recommended levels as measured by standard tests, the investigators found.

The risk of reporting gastrointestinal illness after a beach visit rose as the amount of Enterococcus in the water, measured by QPCR, increased, the researchers found, and the increased risk was greater among children 10 years old and younger.

Enterococcus levels as measured by QPCR were a more accurate predictor of illness risk than the standard testing method.

"In terms of the overall ability to predict health effects, the new method was better," Wade said. Some localities are experimenting on their own with QPCR for testing water quality, he added, although the older method remains the standard for public health advisories.

SOURCE: Epidemiology, May 2008.

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