Their analysis concluded that approximately 11 percent of community-acquired MRSA and soft tissue infections in the study population could be attributed to crop fields fertilized with swine manure. The study is the first to examine the association between high-density livestock operations and manure-applied crop fields and MRSA infections in the community. The results were published online Sept. 16 in JAMA Internal Medicine.

According to the U.S. Food and Drug Administration, nearly 80 percent of antibiotics in the United States are sold for use in livestock feeds. The manure produced by these livestock and applied to crop fields contains antibiotic-resistant bacteria, resistance genes, and about 75 percent of the antibiotics consumed by the animals.

For the study, researchers utilized Geisinger's sophisticated electronic health record system to identify patients with MRSA infections and skin and soft tissue infections. The two groups were compared to patients who never had a MRSA infection. Patients received an exposure score based on their distance from the production, the number of animals at livestock operations, the amount of manure spread on crop fields, and the size of the field. The researchers noted that between 2005 and 2010 there were about 3,000 patients with MRSA and 50,000 with skin and soft tissue infections who were diagnosed and treated in the Geisinger Health System.

Of these cases, 1,539 cases of community-associated MRSA and 1,335 cases of health-care-associated MRSA met the study requirements. The researchers found a significant association between community-associated MRSA and application of swine manure to crop fields. A similar but weaker association was found between swine operations and community-associated MRSA. No association was found between dairy farms and MRSA infections.

"The study shows the utility of electronic health records for demonstrating the unrecognized public health consequences of operations with environmental impacts," said Brian Schwartz, M.D., MS, senior author and environmental epidemiologist who splits his time between Geisinger Health System and Bloomberg School's Department of Environmental Health Sciences.

Funding for the research was provided by the New York University-Geisinger Seed Grant Program, the Johns Hopkins Center for a Livable Future, the Johns Hopkins Sommer Scholarship and the National Institute of Environmental Health Sciences Training Grant ES07141.