High vancomycin minimum inhibitory concentration is a predictor of mortality in meticillin-resistant Staphylococcus aureus bacteraemia

Abstract

Failure of vancomycin in the treatment of meticillin-resistant Staphylococcus aureus (MRSA) bacteraemia has been reported despite full susceptibility of the organism to vancomycin. A retrospective observational cohort study including 137 patients with MRSA bacteraemia was performed at two centres in South Korea during 2009–2010. A total of 137 patients with MRSA bacteraemia receiving vancomycin therapy were enrolled during the study period. Isolates from 13 (9.5%) of the 137 patients had minimum inhibitory concentrations (MICs) ≥1 μg/mL. The 30-day cumulative survival was 53.8% for patients infected with isolates having a MIC ≥ 1 μg/mL and 79.8% for patients infected with isolates having a MIC < 1 μg/mL (log-rank test, P = 0.026). Vancomycin MIC ≥ 1 μg/mL [hazard ratio (HR) = 7.0, 95% confidence interval (CI) 2.2–22.1; P = 0.001], nosocomial acquisition of bacteraemia (HR = 5.4, 95% CI 1.4–20.1; P = 0.013), rapidly fatal underlying diseases (HR = 20.5, 95% CI 3.9–106.4; P < 0.001), presentation with septic shock (HR = 8.4, 95% CI 3.0–23.3; P < 0.001), presence of complicated infections (HR = 5.6, 95% CI 2.0–15.8; P = 0.001) and persistent MRSA bacteraemia for ≥3 days (HR = 4.2, 95% CI 1.4–12.7; P = 0.012) were independent predictors of 30-day mortality in patients with MRSA bacteraemia. In patients with high Pitt bacteraemia scores (Pitt score ≥2), the delay in initiation of vancomycin therapy was significantly different between non-survivors and survivors (2.4 days vs. 1.1 days; P = 0.012). Vancomycin MIC ≥ 1 μg/mL had a significant impact on mortality of patients with MRSA bacteraemia. These findings support early consideration of alternative anti-MRSA agents in patients with MRSA bacteraemia who have high vancomycin MICs as well as prompt initiation of anti-MRSA treatment in patients with MRSA bacteraemia, especially those with high Pitt scores.