CDC spokeswoman Brittany Behm said that antibiotic-resistant CRE are found naturally in coastal waters, including those in the United States.
"The risk of getting an antibiotic-resistant infection from exposure to sewage-contaminated recreational water is not well studied," Behm said in an e-mail to DNews. "Data from the U.S. show that exposure to healthcare settings is the predominant risk factor for getting antibiotic-resistant infections."
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But last fall, scientists at the U.S. Environmental Protection Agency reported CRE in seven sewage treatment plants across the country, including one in Southern California.
Other researchers have found similar results in sewage treatment plants in Brazil, Portugal, Poland, India and Japan.
Alvarez believes the only way to stop this threat is by developing new treatments, but also changing human behavior. Antibiotics must be more restricted, he said, and perhaps hospital sewage treatment plants need to be tested and become self-contained so they don't discharge drug-resistant organisms into local waterways.
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"We need both technological innovation, better ways to kill and disinfect, making sure that they don't spread through sewage or wastewater treatment plants," he said. "We also need more policy and related non technical solutions. Number one is to avoid the misuse of antibiotics."
Olympic officials say the risk of infection is small, but are warning athletes to shower after leaving the water or shoreline.
EPA spokeswoman Cathy Milbourn says that the agency will continue to track the evolving science on how wastewater treatment affects antibiotic-resistant bacteria.
"Wastewater is typically disinfected prior to discharge," she said. "EPA is not familiar with any conclusive scientific studies that show that antibiotic-resistant bacteria are more resistant to being killed or deactivated by wastewater disinfection processes than non-antibiotic-resistant bacteria."