Living Near Livestock Raises MRSA Risk

A new study by researchers from the Johns Hopkins Bloomberg School of Public Health and Dutch colleagues found that regional density of livestock is an important risk factor for people without direct contact with the animals.

People who live near livestock or in livestock farming communities may be at higher risk of acquiring MRSA (methicillin-resistant Staphylococcus Aureus), researchers from the Johns Hopkins Bloomberg School of Public Health, the Dutch Institute for Public Health and the Environment (RIVM), and VU University Medical Center in Amsterdam report. Their study, which is featured in the November issue of Emerging Infectious Diseases and detailed in a Bloomberg School news release on Oct. 10, compared livestock density, place of residence, and existing information on risk factors. They concluded regional density of livestock is an important risk factor for nasal carriage of livestock-associated (LA) MRSA, both for those with and without direct contact with livestock.

The release explains that Staphylococcus aureus is a pathogen that can cause a range of illnesses, from minor to life-threatening skin, bloodstream, respiratory, urinary, and surgical site infections. Nasal carriage, the indicator under study here, "does not indicate that someone is infected with MRSA, it is associated with increased risks of eventual infection. Moreover, in this study it is a measure of exposure to MRSA," the release states.

"In the past, MRSA has been largely associated with hospitals and other health care facilities, but in the last decade the majority of infections have been acquired in the community outside of a health care setting," said Ellen Silbergeld, PhD, co-author of the study and a professor with the Bloomberg School of Public Health's Department of Environmental Health Sciences. The authors report this study is the first to suggest the importance of indirect routes of transmission of livestock-associated MRSA. "In the Netherlands, LA-MRSA was first found in 2003 and was initially almost exclusively found in persons with direct contact to livestock. In recent years, LA-MRSA is found with increasing frequency in community-dwelling individuals with no known contact with livestock. It is important to determine the routes of transmission outside of the farms since this may have important consequences for public health," said Jan Kluytmans, MD, Ph.D., co-author of the study and professor of Medical Microbiology and Infection Control, VU University Medical Center Amsterdam and Amphia Hospital Breda, the Netherlands.

"Using logistic regression, we found that as the density of veal calves, pigs, or cattle doubles in a specific area, the odds of carrying LA-MRSA increases between 24 percent and 77 percent, depending on the animal. These results challenge us to understand how these exposures could be occurring," said Beth Feingold, Ph.D., MPH, MESc, lead author of the study, a Bloomberg School graduate, and the Glenadore and Howard L. Pim Postdoctoral Fellow in Global Change at the Johns Hopkins Zanvyl Krieger School of Arts and Sciences. "This work has potential policy implications for MRSA surveillance in countries with a substantial percentage of total MRSA cases being livestock-associated MRSA. Controlling the spread of livestock-associated MRSA requires attention to community members in animal-dense regions who are otherwise unaffiliated with livestock farming."

"Swine production is a significant industry in the Netherlands, but its density and scale are much less than in the United States. Future work should investigate the relationship between intensive livestock operations in the U.S. and exposures to drug-resistant microbes, including MRSA," Silbergeld said.

"Livestock Density as Risk Factor for Livestock-associated Methicillin-Resistant Staphylococcus aureus, the Netherlands" was written by Feingold, Silbergeld, Frank Curriero, Brigitte Van Cleef, Max Heck and Kluytmans. Their research was funded by the Johns Hopkins Center for a Livable Future and the Pew Charitable Trusts.

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    April 2021


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