Coagulase-negative staphylococcal bloodstream infections: Does vancomycin remain appropriate empiric therapy?

OBJECTIVES

It is unknown if vancomycin minimal inhibitory concentrations (MICs) have increased in coagulase-negative staphylococci (CoNS) or whether vancomycin remains appropriate empiric therapy.

METHODS

We performed a retrospective study at a single tertiary care center over 8 years. Adult inpatients with ≥2 positive blood cultures for CoNS within a 48-h period were eligible. Susceptibilities were performed by automated broth based-microdilution. Changes in antimicrobial susceptibility were analyzed using logistic regression. The clinical characteristics and outcomes of patients with bloodstream infections (BSI) were compared by MIC.

RESULTS

Of 308 episodes of possible CoNS bacteremia, the vancomycin MIC was ≤1 μg/mL in 80 (26%) isolates, 2 μg/mL in 223 (72.4%) isolates and 4 μg/mL in 5 (1.6%) isolates. No isolates were resistant. We observed an 11-fold increased chance of having an isolate with a vancomycin MIC ≤1 μg/mL in 2009-2011 compared with 2004-2008 (OR 10.8, 95% CI 6.0-19.5, p < 0.05). In 152 patients with BSI, the median days of bacteremia, hospital mortality and readmissions at 30 days were similar in BSI caused by isolates with high vancomycin MICs (2-4 μg/mL) and low vancomycin MICs (≤1 μg/mL).

CONCLUSIONS

We conclude vancomycin is still appropriate empiric therapy for CoNS BSIs. CoNS vancomycin MICs decreased over the study period despite widespread use of vancomycin.