Epidemiology of invasive community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections in Monroe County, New York

Background: CA-MRSA is widespread and the incidence is increasing. Defining the population at risk for severe disease will assist in targeting prevention. We describe the epidemiology of invasive CA-MRSA over a six-year period in Monroe County, NY. Methods: Population-based laboratory surveillance of MRSA sterile cultures was performed from 2005 through 2010. Cases were classified as CA-MRSA or healthcare-associated (HA-MRSA) based on chart review for established healthcare risk factors. MRSA isolates underwent strain-typing. Characteristics of CA-MRSA and HA-MRSA were compared using odds ratios (OR) and 95% confidence intervals (CI) from logistic regression. Results: 2,077 incident cases were identified, of which 198 (10%) were CA-MRSA. The annual incidence of invasive CA-MRSA varied from 2.7 to 5.5 vs. 31.5 to 54.4 per 100,000 population for HA-MRSA. Compared to HA-MRSA, CA-MRSA cases were younger (51 vs. 65 years; p<0.0001), more likely to be injection drug users (IDUs) (OR:5.36; CI:3.17-9.06) and smokers (OR:2.51; CI: 1.80-3.50), and more likely to have endocarditis (OR:1.78; CI:1.04-3.06), skin and soft tissue infections (OR: 3.41; CI:2.50-4.67), and joint infections (OR:4.78; CI: 3.40-6.74). IDUs with CA-MRSA were more likely than other CA cases to be hospitalized (p=0.018), have a longer hospital stay (24 vs. 11 days, p=0.0064), endocarditis (OR: 13.42; CI: 4.48-40.21), septic shock (p=0.0488), and have USA300 MRSA strains (p=0.0015) carrying Panton-Valentine leukocidin (p<0.0001). Conclusions: In Monroe County, NY, the incidence of invasive CA-MRSA is stable. Severe CA-MRSA is associated with IDUs. Our study highlights the importance of programs targeting IDUs in order to decrease CA-MRSA in this population.