Vancomycin minimum inhibitory concentrations and lethality in Staphylococcus aureus bacteremia.

Area of Science:

• Infectious Diseases
• Clinical Microbiology
• Pharmacology

Background:

• Increasing antibiotic resistance in Staphylococcus aureus, including penicillin and oxacillin resistance.
• Emergence of vancomycin-intermediate and vancomycin-resistant Staphylococcus aureus isolates.
• Previous studies suggest a correlation between higher vancomycin minimum inhibitory concentrations (MICs) and increased lethality, even within the susceptible range.

Purpose of the Study:

• To investigate the association between vancomycin MICs and clinical outcomes in patients with Staphylococcus aureus bacteremia.
• To compare vancomycin MICs determined by two different methods (microdilution and Etest) and their correlation with patient lethality.

Main Methods:

• Retrospective analysis of hospitalized patients with Staphylococcus aureus bacteremia.
• Comparison of vancomycin MICs using microdilution and Etest methods.
• Correlation of MIC values (categorized as <2 mg/L and ≥2 mg/L) with patient lethality.

Main Results:

• Lethality was 25% for isolates with microdilution MICs <2 mg/L and 33% for MICs ≥2 mg/L.
• Lethality was 23% for isolates with Etest MICs <2 mg/L and 44% for MICs ≥2 mg/L.
• A slight trend of increased lethality with higher MICs was observed, but did not reach statistical significance.

Conclusions:

• The study indicated a potential trend between higher vancomycin MICs and increased lethality in Staphylococcus aureus bacteremia.
• The observed difference lacked statistical significance, likely due to a small patient cohort.
• Prospective studies are recommended to further elucidate this correlation and inform clinical antimicrobial therapy decisions.