An investigation of antibiotic susceptibility to empiric therapy for community-associated methicillin-resistant Staphylococcus aureus.

OBJECTIVE: To analyze antibiotic susceptibility patterns of community-associated methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained from skin and soft tissue infections among Wisconsin outpatients. DESIGN: Retrospective genotype testing. SETTING: Isolates were forwarded to the Wisconsin State Laboratory of Hygiene and Marshfield Labs from clinical laboratories throughout Wisconsin. METHODS: MRSA isolates submitted during April, 2010-February, 2012 underwent genotype analysis using pulsed-field gel electrophoresis. Antibiotic susceptibility patterns were determined for all isolates identified by electrophoresis subtyping as strain type USA300, and pattern comparisons were made by public health region. RESULTS: Among 835 MRSA isolates submitted, 217 (26%) were genotyped. Of these, 152 (70%) were USA300 MRSA. Among the 152 USA300 isolates, 95% were susceptible to clindamycin and 99% were susceptible to tetracycline and trimethoprim-sulfamethoxazole. The proportion of clindamycin-susceptible isolates from the southern region was significantly lower when compared to the other 4 regions combined (P = 0.03). One southern region clindamycin-resistant isolate was also resistant to trimethoprim-sulfamethoxazole. CONCLUSIONS: USA300 MRSA was the predominant strain isolated from outpatient skin and soft tissue sites. Antibiotic susceptibility patterns among Wisconsin USA300 MRSA isolates are similar to patterns found in national studies. Local providers should continue to follow national practice guidelines for treatment of outpatient skin infections. A cluster of 4 clindamycin-resistant isolates and 1 trimethoprim-sulfamethoxazole resistant isolate was detected in the southern region, warranting continued surveillance for antibiotic resistance among community-associated MRSA isolates.