Mupirocin resistance among consecutive isolates of oxacillin-resistant and borderline oxacillin-resistant Staphylococcus aureus at a university hospital

Mupirocin resistance was determined in consecutive oxacillin-resistant and borderline oxacillin-resistant Staphylococcus aureus clinical isolates collected over 14 months at a university hospital during 1991 and 1992. Twenty of 86 (23%) oxacillin-resistant and borderline oxacillin-resistant S. aureus isolates were mupirocin resistant; 80% were high-level resistant. Prior mupirocin use was a significant risk factor (relative risk, 6.08; 95% confidence interval, 3.7 to 9.99). Seven of 20 resistant isolates were distinct strains, as determined by pulsed-field gel electrophoresis typing. Two instances of clonal dissemination of a single strain occurred, but several other distinct mupirocin-resistant strains were documented. Mupirocin resistance was unexpectedly common among these isolates.