Spatial and molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) infection in relation to animal feeding operations in Pennsylvania

Traditionally, methicillin resistant Staphylococcus aureus (MRSA) has been a nosocomial pathogen, but in the past decade the epidemiology of MRSA has changed. Three major epidemiologic profiles have emerged, hospital- (HA), community- (CA), and livestock-associated (LA) MRSA. Two of the three, CA and LA, have been linked to environmental exposures, specifically animal husbandry and industrialized animal production. We evaluated associations of MRSA with animal feeding operations (AFOs) using 10 years of electronic health record (EHR) data from the Geisinger Clinic (GC). GC provides primary care services from 41 community practice clinics and 4 hospitals in a 31-county region of central and northeastern Pennsylvania, a region with a large number of AFOs. Data were available from > 440,000 primary care patients involving > 157,000,000 records. The number of diagnosed MRSA infections rose from 6 in 2003 to 436 in 2009, with increases in both HA and CA-MRSA; during these years, > 60% of total cases were CA-MRSA. In the 38 Geisinger and bordering counties there are 1350 AFOs with 328,000 animal equivalent units (AEUs, 1 AEU = 1,000 pounds live weight), including 170 concentrated AFOs (CAFOs). To investigate the association between AFOs and human MRSA infection we defined four patient groups using specific ICD-9 codes: (1) community-onset MRSA without health care system contact risk factors; (2) hospital-onset MRSA with risk factors; (3) skin and soft tissue infections (SSTIs); and (4) controls. The spatial distribution of the 1926 MRSA cases will be examined in various definitional groupings to improve sensitivity and specificity of the case definition, and logistic regression will be used to explore associations with the environment. A random sample of isolates from 25 patients from each of groups (1) and (2) will undergo genotyping by multilocus sequence typing (MLST), spa typing and ascertainment of presence of PVL toxin genes.