Is reduced vancomycin susceptibility a factor associated with poor prognosis in MSSA bacteraemia?

Area of Science:

• Infectious Diseases
• Clinical Microbiology
• Antimicrobial Resistance

Background:

• Conflicting data exists regarding the impact of vancomycin Minimum Inhibitory Concentration (MIC) on outcomes for Staphylococcus aureus bacteraemia.
• Vancomycin remains a critical antibiotic for treating Methicillin-Susceptible Staphylococcus aureus (MSSA) infections.

Purpose of the Study:

• To investigate the association between vancomycin MIC levels (≥1.5 mg/L) and short-term (14-day) and medium-term (30-day) mortality in patients with MSSA bacteraemia.
• To explore the relationship between reduced vancomycin susceptibility (RVS) and complicated bacteraemia rates.

Main Methods:

• A prospective cohort study involving 135 adult patients with MSSA bacteraemia.
• Genotyping of isolates using Pulse Field Gel Electrophoresis (PFGE) and analysis of accessory gene regulator (agr) type and δ-haemolysin absence.
• Multivariate analysis using Cox regression, incorporating a propensity score for RVS.

Main Results:

• Twenty-nine percent of MSSA isolates exhibited vancomycin MIC ≥1.5 mg/L.
• No significant differences in agr distribution or δ-haemolysin absence were observed between RVS and non-RVS isolates.
• RVS was not associated with increased 14-day or 30-day mortality, nor with higher rates of complicated bacteraemia.

Conclusions:

• Contrary to some previous findings, this study did not establish a link between reduced vancomycin susceptibility and increased mortality in MSSA bacteraemia.
• The study also found no association between RVS and higher rates of complicated bacteraemia in this patient cohort.