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'Superbug' found in US wastewater treatment plants

UM study suggests plant workers at risk for antibiotic-resistant infection

Tim Wheeler

10:25 AM EST, November 6, 2012

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Hospitals aren't the only places where people can pick up a nasty "superbug.'' A University of Maryland-led team of researchers has found methicillin-resistant Staphylococcus aureus, or MRSA, at sewage treatment plants in the mid-Atlantic and the Midwest.

MRSA is a well-known problem in hospitals, where patients have picked up potentially fatal bacterial infections that do not respond to antibiotic treatment.  But since the late 1990s, it's also been showing up in otherwise healthy people outside of health-care facilities, prompting a search for sources in the wider community.

"MRSA infections acquired outside of hospital settings – known as community-acquired MRSA or CA-MRSA– are on the rise and can be just as severe as hospital-acquired MRSA," said Amy R.   Sapkota, assistant professor in the Maryland Institute for Applied Environmental Health and research study leader. "However, we still do not fully understand the potential environmental sources of MRSA or how people in the community come in contact with this microorganism.

Sewage plants are one possible source, because infected people can shed MRSA through their feces, as well as from their nose and skin.  The resistant bacteria have been detected before in wastewater plants in Sweden, but researchers at UM's School of Public Health say this study, conducted in parnership with the University of Nebraska Medical Center, is the first to spot it in US facilities.  Their findings were published in the November issue of Environmental Health Perspectives.

Researchers at the two schools collected wastewater samples at two Mid-Atlantic and two Midwestern treatment plants, which were not identified in the paper. They said they chose the plants, in part, because treated effluent from these plants is reused as "reclaimed wastewater" and sprayed on fields to irrigate and fertilize them. The researchers wanted to see if MRSA could be spread that way.

The study found MRSA in 83 percent of the raw sewage entering the plants, but the incidence declined as the sewage progressed through the treatment process. Only one plant still had the bacteria in its fully treated water, researchers found, and that facility did not regularly use chlorination to finish disinfecting its wastewater.

"Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater," says Rachel Rosenberg Goldstein, environmental health doctoral student and the study's first author. "Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater."

Besides sewage plants, living near livestock farms may be another potential source of exposure.  A recent study in the Netherlands led by researchers from Johns Hopkins' Bloomberg School of Public Health found the risks of getting MRSA there highest among people living in a region with high concentrations of cattle and pigs.