A recent study examining the prevalence of methicillin and multidrug resistant Staphyloccocus aureus (MRSA and MDRSA) among farm workers has reported that livestock-associated strains of both bacteria were present only in individuals employed at “industrial livestock operations” (ILOs) and not those employed at “antibiotic-free livestock operations” (AFLOs). Jessica Rinsky, et al., “Livestock-Associated Methicillin and Multidrug Resistant Staphylococcus aureus Is Present among Industrial, Not Antibiotic-Free Livestock Operation Workers in North Carolina,” PLoS One, July 2013. Researchers with the University of North Carolina, George Washington University and Johns Hopkins University’s Bloomberg School of Public Health reportedly examined nasal swab samples from 99 ILO and 105 AFLO workers, finding that of the 41 ILO and 42 AFLO workers carrying S. aureus bacteria, 7 percent of each group tested positive for MRSA. In addition, the study’s authors identified MDRSA in 37 percent of ILO S. aureus carriers and 19 percent of AFLO S. aureus carriers, noting that the S. aureus clonal complex (CC) unique to livestock “was observed only among workers and predominated among ILO (13/34) compared with AFLO (1/35) S. aureus-positive workers.”

“Despite similar S. aureus and MRSA prevalence among ILO and AFLOexposed individuals, livestock-associated MRSA and MDRSA… were present only among ILO-exposed individuals,” the study elaborated. “These findings support growing concern about antibiotic use and confinement in livestock production, raising questions about the potential for occupational exposure to an opportunistic and drug-resistant pathogen, which in other settings including hospitals and the community is of broad public health importance.”