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

Area of Science:

• Infectious Diseases
• Clinical Microbiology
• Antimicrobial Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) prevalence increased significantly from 18% in 1997 to 51% in 2002 at the Wisconsin Veterans Home.
• This highlights a growing challenge in managing Staphylococcus aureus infections.

Purpose of the Study:

• To investigate the antibiotic sensitivity patterns of MRSA and methicillin-sensitive S. aureus (MSSA) isolates.
• To examine changes in antibiotic utilization during the period of increasing MRSA resistance.
• To identify potential drivers for MRSA overgrowth.

Main Methods:

• Determined antibiotic sensitivity profiles for MRSA and MSSA.
• Analyzed antibiotic usage data between two distinct time periods.
• Correlated changes in antibiotic use with shifts in MRSA prevalence.

Main Results:

• MRSA isolates were typically resistant to quinolones, while MSSA remained sensitive.
• Both MRSA and MSSA demonstrated sensitivity to TMP-sulfa.
• A 42% increase in quinolone use and a 37% decrease in TMP-sulfa use coincided with the rise in MRSA.

Conclusions:

• Findings suggest that the substitution of TMP-sulfa with quinolones may be contributing to the selection and overgrowth of MRSA.
• The observed association requires further investigation and confirmation to establish causality.