Prospective multicenter surveillance identifies Staphylococcus aureus infections caused by livestock-associated strains in an agricultural state

We conducted a surveillance study to investigate the epidemiology of Staphylococcus aureus infections in Iowa, using a convenience sample. Diagnostic laboratories submitted 20 S. aureus isolates per month for a 20-month period between 2011 and 2013. Of the 2226 isolates analyzed, 73.6% were methicillin-resistant S. aureus (MRSA) and 26.4% were methicillin-susceptible S. aureus (MSSA). S. aureus infections in 25 patients (1%) were caused by ST398- and ST9-associated strain types, and appeared to be a common occurrence in areas of the state with the highest numbers of hogs and hog farms. Twenty nine (5.1%) of MSSA isolates and 10 (40.0%) livestock-associated strains were multi-drug resistant.