Using MRSA Screening Tests To Predict Methicillin Resistance in Staphylococcus aureus Bacteremia

Area of Science:

• Infectious Diseases
• Clinical Microbiology
• Antimicrobial Stewardship

Background:

• Bloodstream infections caused by Staphylococcus aureus are a significant clinical concern.
• Empirical treatment often includes vancomycin for methicillin-resistant S. aureus (MRSA), despite potential harms.
• Predicting MRSA bacteremia is crucial for appropriate empirical therapy selection.

Purpose of the Study:

• To investigate the correlation between MRSA colonization screening and resistance in S. aureus bacteremia.
• To determine if MRSA screening can guide the necessity of empirical vancomycin therapy.
• To evaluate the predictive values of different MRSA screening criteria.

Main Methods:

• Retrospective review of consecutive S. aureus bacteremias over a 5-year period at two tertiary care hospitals.
• Evaluation of MRSA colonization using three criteria: 30-day testing, ever-positive status, and known-positive status.
• Analysis of negative and positive predictive values for MRSA screening.

Main Results:

• Of 409 S. aureus bacteremias, 26.2% were MRSA.
• MRSA screening within 30 days showed high negative predictive values (NPV >90% and >95% at specific MRSA prevalence thresholds).
• Different screening criteria demonstrated varying NPVs, with MRSA screening showing positive predictive values over 50% in MRSA-colonized patients at low prevalence.

Conclusions:

• MRSA screening is a valuable tool for guiding empirical vancomycin therapy decisions.
• It can help avoid vancomycin use and associated complications in stable patients.
• The utility of MRSA screening is most pronounced in settings with low-to-moderate MRSA bacteremia proportions.