MRSA in waste treatment water poses potential risk

BMJ 2012; 345 doi: (Published 13 November 2012) Cite this as: BMJ 2012;345:e7673
  1. Bob Roehr
  1. 1Washington, DC

Drug susceptible and drug resistant Staphylococcus aureus has been identified in about half of the intake and egress samples gathered at four waste water treatment sites in the United States. It raises potential public health concerns for how this water is used.

The study is believed to be the first of its kind in the United States and was prompted by an earlier similar report from Sweden.

Researchers gathered 44 samples at various times of the year from two waste water treatment plants in the mid-Atlantic region and an additional two sites in the Midwest. Each 300 mL sample was filtered; the filters were cultured for S aureus; and polymerase chain reaction technology was used to identify key genes of the bacteria.

“The odds of samples being MRSA-positive decreased as treatment progressed: 10 of 12 (83%) influent samples were MRSA-positive, while only 1 of 12 (8%) effluent samples were MRSA-positive,” the authors wrote in the paper published in Environmental Health Perspectives.1

S aureus can be shed from humans into waste water through bathing and swimming and in fecal matter. Commercial swine and poultry operations can also be a major source of the bacterium in the environment.

Concern arises because increasingly this waste “grey water” is being used directly for purposes such as irrigating agricultural crops, watering golf courses, and creating artificial snow at ski resorts. Little is known about the disease risk of common pathogens that are aerosolized or deposited on surfaces where people might come into direct contact with them.

Speaking to the BMJ, the study’s senior author, Amy R Sapkota, cautioned that the work was very preliminary and that its meaning was far from clear. Most people exposed to S aureus, even those colonized with the bacterium, do not develop disease. That depends on a dynamic of infectious dose and host susceptibility.

Drinking water, unlike “grey water,” undergoes additional steps of purification, such as chlorination, designed to kill the pathogen.

The study was conducted by the Maryland Institute for Applied Environmental Health at the University of Maryland School of Public Health, under a grant from the National Institute for Occupational Safety and Health.


Cite this as: BMJ 2012;345:e7673