Relationship between vancomycin tolerance and clinical outcomes in Staphylococcus aureus bacteraemia

Area of Science:

• Infectious Diseases
• Clinical Microbiology
• Pharmacology

Background:

• Clinical significance of vancomycin Minimum Inhibitory Concentration (MIC) in Staphylococcus aureus bacteraemia (SAB) is established.
• The impact of vancomycin tolerance (VT) on SAB outcomes remains largely unknown.

Purpose of the Study:

• To compare the frequency of clinical failure between patients with VT and non-VT Staphylococcus aureus isolates in SAB.
• To investigate the association between vancomycin tolerance and clinical failure in SAB.

Main Methods:

• Retrospective cohort study of patients with SAB.
• Vancomycin MIC and MBC determined by broth microdilution; VT defined as MBC/MIC ratio ≥32.
• Clinical failure defined as a composite of 30-day mortality, non-resolving symptoms, and 60-day recurrence.

Main Results:

• 26.7% of patients had VT isolates.
• VT was significantly associated with clinical failure in both unadjusted and multivariable analyses (aRR, 1.74; P<0.001).
• This association remained consistent across methicillin-susceptible and methicillin-resistant S. aureus, and in cases treated with β-lactam therapy.

Conclusions:

• Vancomycin tolerance is associated with increased clinical failure in SAB, irrespective of methicillin susceptibility or treatment.
• VT may reduce the efficacy of cell-wall-active therapies or indicate other poor-outcome-associated factors.
• Future research should explore bactericidal, non-cell-wall-active agents for VT SAB treatment.