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BALTIMORE—When it comes to swimming in lakes and streams, we all dream of finding that secluded spot where we can drift without interruption. Well, according to studies published recently in the journals Applied and Environmental Microbiology and Water Research, those secluded spots may also be healthier for us, as crowded waterways may increase our risk for parasitic infection.
Researchers at the Johns Hopkins Bloomberg School of Public Health studied the human and microbial activity of a particular beach in Maryland, taking regular water samples on Wednesdays (few swimmers) and Saturdays (many swimmers) over an 11-week period in the summer of 2006. They then looked for spores and parasites of Cryptosporidium parvum and Giardia lamblia, two parasites that can cause nausea, vomiting, and diarrhea.
They found that parasite levels were highest when the beaches were busiest, suggesting that swimmers may be stirring up the parasites from the sediments. This means an increased risk for infection.
Unfortunately, environmental agencies generally don’t test for these parasites when determining beach safety and generally perform their tests when there is little human activity. “Our research suggests it would be best to test the water when the beach is active to determine if it is safe for recreational use,” says Dr. Thaddeus Graczyk, a Bloomberg professor and co-author of both studies.
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