Antimicrobial use and methicillin-resistant Staphylococcus aureus in a large nursing home.

INTRODUCTION

In 1997, 18% of Staphylococcus aureus clinical isolates at the Wisconsin Veterans Home were resistant to methicillin. By 2002, 51% were resistant.

METHODS

We determined the antibiotic sensitivity pattern of our methicillin-resistant S. aureus (MRSA) isolates as well as changes in utilization of specific antibiotics between two time periods. We reasoned that antibiotics with activity against methicillin-sensitive S. aureus (MSSA), but not MRSA, might be driving the overgrowth of MRSA.

RESULTS

In our facility, MRSA is usually resistant to quinolones; MSSA is usually sensitive. Both MSSA and MRSA are usually sensitive to TMP-sulfa. An increased percentage of S. aureus resistant to methicillin (18%) was associated with a 42% increase in quinolone use and a 37% decrease in TMP-sulfa use.

CONCLUSION

Our analysis and previous reports suggest that replacement of TMP-sulfa by quinolones could be selecting MRSA in our facility. This conclusion, however, is speculative, based on association, and requires confirmation.