Rapid dissemination of Staphylococcus aureus with classic oxacillin resistance phenotype at a new university hospital.

To determine the prevalence rates of oxacillin-resistant Staphylococcus aureus (ORSA) at a new university hospital since its opening, the results of disk diffusion tests on all clinical isolates, recovered between 1990 and 1998 at the National Cheng Kung University Hospital, were reviewed. In order, to investigate the mechanisms of oxacillin resistance among strains of S. aureus in Taiwan, MICs were determined by an agar dilution method, and polymerase chain reaction and colony hybridization assays were performed on 288 isolates collected during November 1998 to detect the mecA gene. The prevalence rates of ORSA increased rapidly from 14.1% in 1990 to 61.0% in 1998. The increasing rates were most rapid in the first four-year period, ranging from 11.6 to 106.7% per year, and became steady after 1994, ranging from 1.8% to 11.6%. Of 288 clinical isolates collected in November 1998, 206 (71.5%) were resistant to oxacillin (MIC >/= 16 mg/L), and four were borderline resistant (MIC 2-8 mg/L). All 210 strains possessed the mec A gene (classic resistance). The present study demonstrated that ORSA could disseminate in a new hospital with great speed, and indicated that all ORSA strains in Taiwan revealed classic resistance phenotype. Copyright 2000 The Hospital Infection Society.