Swimmers at crowded public beaches are likely to bring home more than a bit of sand in their bathing suits, according to U.S. researchers, who said as many as one in three swimmers may be exposed to contagious staph bacteria.They said people who swim in subtropical marine waters have a 37 percent higher risk of being exposed to staph bacteria, including an antibiotic resistant staph known as Methicillin-resistant Staphylococcus aureus, or MRSA."We think that people are the instruments for bringing their organisms into the water and leaving it behind," Dr. Lisa Plano of the University of Miami told reporters at the American Association for the Advancement of Science meeting in Chicago on Friday."I don't know if that is the only source. The bacteria may still be in the sand left over from other people, but we haven't studied that. These are things we plan to do in the future."People who have open wounds or are immune compromised have the greatest risk of infection, she said.In one experiment with more than 1,000 bathers on a popular Florida beach, people spent 15 minutes dunking themselves in the sea, then bringing sea water back with them in a jug.They then tested the water for staph and MRSA and found 37 percent of the samples contained staph, and 3 percent of those contained MRSA."I don't think you should fear going to the beach," Plano said, particularly if they take a few simple precautions.She recommends people shower before going to the beach, to keep from depositing their own germs into the water. And she suggests they shower once they leave, to wash off any pathogens."If you don't go into the water with a gaping wound, you should be fine," Plano said.