Community-Associated Methicillin-Resistant Staphylococcus aureus and HIV: Intersecting Epidemics

Background. Single-site studies have suggested a link between human immunodeficiency virus (HIV) and community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). Methods. Population-level incidence of HIV-infected patients with CA-MRSA versus community-associated methicillin-susceptible S. aureus (CA-MSSA) infection was assessed in the Cook County Health and Hospitals System (CCHHS), a multi-hospital and ambulatory care center. Rates in zip codes, including those with a high density of individuals with prior incarceration (ie, high-risk zip codes), were calculated. We did a nested case-control analysis of hospitalized HIV-infected patients with S. aureus skin and soft-tissue infections (SSTIs). Results. In CCHHS, the incidence of CA-MRSA SSTIs was 6-fold higher among HIV-infected patients than it was among HIV-negative patients (996 per 100,000 HIV-infected patients vs 157 per 100,000 other patients; P < .001). The incidence of CA-MRSA SSTIs among HIV-infected patients significantly increased from 2000-2003 (period 1) to 2004-2007 (period 2) (from 411 to 1474 cases per 100,000 HIV-infected patients; relative risk [RR], 3.6; P < .001), with cases in period 1 clustering in an area 6.3 km in diameter (P = .035) that overlapped high-risk zip codes. By period 2, CA-MRSA SSTIs among HIV-infected patients were spread throughout Cook County. USA300 was identified as the predominant strain by pulsed-field gel electrophoresis (accounting for 86% of isolates). Among hospitalized HIV-infected patients, the incidence of CA-MRSA increased significantly from period 1 to period 2 (from 190 to 779 cases per 100,000 HIV-infected patients; RR, 4.1; P < .001). Risks for CA-MRSA by multivariate analysis were residence in alternative housing (eg, shelters), residence in high-risk zip codes, younger age, and infection in period 2. Conclusions. HIV-infected patients are at markedly increased risk for CA-MRSA infection. This risk may be amplified by overlapping community networks of high-risk patients that may be targets for prevention efforts.