Published in the journal Environmental Health Perspectives, the findings show that methicillin-resistant Staphylococcus aureus (MRSA) is present at two water treatment facilities in the Midwest and two facilities in the mid-Atlantic region.
"Our findings raise potential public health concerns for wastewater treatment plant workers and individuals exposed to reclaimed wastewater," study researcher Rachel Rosenberg Goldstein, a doctoral student in environmental health at the University of Maryland's School of Public Health, said in a statement. "Because of increasing use of reclaimed wastewater, further research is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated wastewater."
MRSA is of particular importance in the public health realm because it is resistant to the usual antibiotics that are used to fight staph. It's particularly common in hospitals, what is known as hospital-acquired MRSA, though community-acquired MRSA is also possible (like if you are living in a crowded area, such as a jail or childcare center, or if you play certain contact sports), according to the Mayo Clinic.
The study included samples from the four different water treatment plants as they went through the treatment process. MRSA was found in half of all the samples gathered, while MSSA (methicillin-susceptible Staphylococcus aureus) was found in 55 percent of all the samples gathered. MRSA was found in 83 percent of the raw sewage, but researchers noted that as the water went through the treatment process, fewer and fewer samples had MRSA.
By the end of the treatment process, only one of four plants had a sample with MRSA,though researchers noted that this particular plant is known to not chlorinate its water regularly -- a step known as "tertiary treatment."
Researchers were also able to glimpse a snapshot of the kinds of MRSA and MSSA that were in the wastewater facilities -- 93 percent of the MRSA strains identified are resistant to at least two antibiotic classes, as were 29 percent of the MSSA strains.
Researchers said that it was good to find that treated water from wastewater treatment plants were largely rid of MRSA, but they also noted that the tertiary process of chlorination seemed to be important for eliminating the MRSA.