Detection of methicillin-resistant Staphylococcus aureus (MRSA) in backyard pigs and their owners, Michigan, USA

Methicillin-resistant Staphylococcus aureus (MRSA) have been reported in commercially raised pigs and their human handlers, raising concerns of zoonotic transmission. To determine whether MRSA in backyard-raised pigs is commonly transmitted to their human owners, a matched study of this type of pigs and their owners was conducted in selected counties in Michigan. Nasal swabs from matched owner-pig pairs (n = 50 pairs) with a few unmatched pig (n = 3) and human (n = 4) samples were collected and processed using standard isolation and identification protocols. No matched owner-pig pair was found; however, MRSA was isolated from 1/54 (1.9%) human samples and 2/53(3.8%) of the pigs. The single human isolate was not strain type USA100-1100 by pulsed-field gel electrophoresis (PFGE), was sequence type (ST) 8 by multilocus sequence typing (MLST), possessed SCCmec type IVb and agr I and was negative for the Panton-Valentine leukocidin (PVL) toxin gene. The two pig isolates were indistinguishable by PFGE (not USA100-1100), and both isolates were ST5 by MLST, possessed SCCmec type III and agr II and were negative for the PVL gene. Persons raising backyard swine from the selected Michigan counties had MRSA carriage rates similar to that of the general US population, suggesting that their avocational pig exposure did not increase their risk of MRSA.