In what could become a public image problem for wastewater treatment, researchers have found the superbug MRSA (methicillin-resistant Staphylococcus aureus) at four plants in the United States. MRSA is a type of staph bacteria that is resistant to certain antibiotics.

Once confined to hospitals and their patients, the dastardly drug-resistant bacterium causes potentially lethal infections that are a challenge to treat. The superbug is being increasingly found in areas other than hospitals, and in healthy people as well.

Scientists in Sweden have reported finding MRSA in wastewater treatment plants there, but the recent U.S. study is the first to look for the infectious bug in wastewater plants in America. The team of researchers was led by scientists from the University of Maryland School of Public Health. Study leader Amy R. Sapkota, assistant professor in the Maryland Institute for Applied Environmental Health, noted that, "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." But how MRSA has survived outside of hospitals and how healthy people become infected are unsolved mysteries.

Since the superbug is shed from the nose, skin, and feces of infected people, wastewater facilities seemed like a logical place to look.

The research team collected samples at two Mid-Atlantic and two Midwestern treatment plants, plants chosen because their wastewater is used as reclaimed wastewater — meaning that it is given a second life in applications such as landscape irrigation (after it has been cleaned, of course). The results? MRSA, plus a related pathogen, MSSA (methicillin-susceptible Staphylococcus aureus) were discovered in samples from all four plants. MRSA was found in half of the samples, and MSSA was present in 55 percent of them. The team determined that MRSA was present in 83 percent of all the raw, untreated sewage, but that the percentage decreased in samples that had undergone further treatment.

Unfortunately, 93 percent of the MRSA strains and 29 percent of the MSSA strains they discovered were resistant to two or more classes of antibiotics, even those that were developed specifically for treating MRSA infection. Also disturbing to note: The discovery of MRSA strains that were resistant to more antibiotics were also more likely to possess a gene that made them more virulent, in amounts that increased with treatment stage. The harder the battle, the stronger they became. Tertiary chlorination finally did them in, but their tenacity seems cause for concern.

Only one of the four plants tested positive for MRSA in treated water leaving the plant, and that plant was one that did not regularly chlorinate the water.

The study's authors conclude that wastewater treatment plant workers and people who live, work or play near the increasing number of agricultural and recreational sites irrigated with reclaimed wastewater could be exposed to MRSA and MSSA.

The findings were published in the November issue of the journal, Environmental Health Perspectives.

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