For many Americans, swimming at the beach can result in a trip to the doctor, says a study in the Journal of Water and Health.

Swimmers developed significantly more ailments requiring medical attention, such as gastrointestinal illnesses and eye infections, compared with nonswimmers following a day at the beach, researchers found. Nearly 17 percent of swimmers developed at least one new symptom after the outing, compared with 13.5 percent of nonswimmers. About a third of the affected beachgoers missed work or other activities as a result.

An estimated 41 percent of Americans swim in oceans, lakes, rivers or streams every year, according to the study.

Researchers at the U.S. Centers for Disease Control and Prevention and the Environmental Protection Agency analyzed data collected from 54,250 people at nine U.S. beaches, including one in Puerto Rico, from 2003 to 2009. Two-thirds of beachgoers were under age 50. Seven of the beaches were near sewage-discharge points, though all swim areas generally met local and federal guidelines, researchers said.

People were interviewed as they arrived and completed a survey at the end of the day that asked about time spent in the water, contact with sand and algae, and use of goggles and other swim gear.

About three-quarters of beachgoers went into the water, on average. Of these, 65.1 percent immersed their head, 41.3 percent got water in their mouth and 18.5% swallowed the water. Goggles were used by 8.7 percent of swimmers, earplugs by 1.2 percent and nose clips by 0.3 percent.

Health problems were reported during phone interviews 10 to 12 days after the beach visit. The most common were gastrointestinal illnesses, respiratory infections, ear and eye problems, urinary-tract infections and rash. Ear aches were prevalent in children under age 5, while people in their 20s were more likely to develop eye and urinary infections.

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