The changing susceptibilities of methicillin-resistant Staphylococcus aureus at a midwestern hospital: The emergence of “community-associated” MRSA

Background The emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has been well described; however, few studies have reviewed long-term hospital-wide data. Methods This retrospective study of adult patients used the first culture per patient per visit positive for MRSA for 1996 to 2005. Isolates were categorized as community-associated or health care–associated phenotype based on antibiotic susceptibilities. χ2 tests for trend and linear regression analyses were performed. Results The annual prevalence of CA-MRSA increased significantly over the 10-year study period (from 43 of 507 [8.9%] MRSA cultures in 1996 to 672 of 1697 [39.6%] MRSA cultures in 2005; P < .01). The proportion of MRSA cultures obtained within 48 hours of hospital admission increased from 50.5% to 79.5% ( P < .01). The median age of patients with MRSA decreased, from 60 to 49 years ( P < .01). Among the CA-MRSA cases, the proportion of non-Caucasian patients increased from 30.2% to 60.4% ( P < .01) and the proportion of patients categorized as low socioeconomic status increased from 25.6% to 35.6% ( P < .01). Significant consistent trends were not observed for patient sex or body sites of the cultures. Conclusion An increasing number of MRSA with a community-associated phenotype occurred during the 10-year study period. Patterns of decreasing age, increasing non-Caucasian races, and decreasing socioeconomic status were observed among patients with MRSA.