Community-Acquired Methicillin-Resistant Staphylococcus aureus (CA-MRSA): A Retrospective Comparison of Antibiotic Resistance in an HIV Population and a Neighboring Health Care Facility in Tucson, Arizona

Abstract

1College of Pharmacy, University of Arizona 2El Rio Special Immunology Associates Objectives: To compare antibiotic resistance patterns of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) in HIV patients and the general population. We hypothesized that CA- MRSA strains in HIV patients may show a decreased susceptibility to trimethoprim/sulfamethoxazole (TMP/SMX) because of its widespread use for prophylaxis of Pneumocystis carinii pneumonia (PCP) in this population. Methods: Susceptibility reports for all Staphylococcus aureus isolates collected between November 1, 2004 and November 1, 2005 from Special Immunology Associates (SIA), an HIV clinic, and the neighboring Carondelet St. Mary’s Hospital Emergency Center (SMH) were analyzed. Results: Twenty-five cases in HIV patients at SIA (Mean age 40, Race: 21 Caucasian, 4 Hispanic) and 102 cases at SMH (Mean age 37, Race: 45 Caucasian, 34 Hispanic, 12 Native American, 8 African American) were identified as CA-MRSA. More than 95% of patients presented with skin infections and a seasonal peak was identified between June and October. No cases of TMP/SMX resistance were found at either institution despite the fact that 40% of the SIA patients with CA-MRSA had been exposed to TMP/SMX for PCP prophylaxis in the past. Susceptibility varied between SIA and SMH, with significant differences in susceptibility to tetracycline (57% vs. 86%, p<0.001) and levofloxacin (38% vs. 60%, p < 0.001). Erythromycin resistance in both institutions was greater than 90%. Conclusions: All CA-MRSA isolates from an HIV clinic and a neighboring health care facility were susceptible to TMP/SMX. HIV patients with CA-MRSA did not show a decrease in susceptibility to TMP/SMX, despite its routine use for prophylaxis in this population.