Predicting high vancomycin minimum inhibitory concentration isolate infection among patients with community-onset methicillin-resistant Staphylococcus aureus bacteraemia

• High vancomycin MIC MRSA has emerged and spread in the community.
• Certain factors are associated with the risk of high vancomycin MIC MRSA infections.
• A useful clinical score helps physicians decide empirical antimicrobial therapy.

SummaryObjectivesMethicillin-resistant Staphylococcus aureus (MRSA) isolates with an elevated vancomycin MIC ≥2 mg/L have been increasingly identified in many countries. We aimed to develop a clinical score to predict vancomycin MIC ≥2 mg/L in patients with community-onset MRSA bacteraemia.MethodsThis retrospective cohort study enrolled 394 patients with MRSA bacteraemia. Vancomycin MICs of all MRSA isolates were determined by agar dilution method. Clinical characteristics between patients with high (≥2 mg/L) and low (≤1 mg/L) vancomycin MIC MRSA bacteraemia were compared. Independent predictors of high vancomycin MIC isolate infection were identified and used to create a score-based predictive model.ResultsAmong the 394 study patients, 56 (14.2%) had MRSA isolates with a vancomycin MIC ≥2 mg/L. The final regression model included 6 independent predictors: chronic liver disease (adjusted odds ratio [aOR], 2.99; 95% confidence interval [CI], 1.39–6.42), prior recovery of MRSA from respiratory tract specimen (aOR, 2.54; 95% CI, 1.15–5.61), end-stage renal disease (aOR, 2.53; 95% CI, 1.33–4.78), severe sepsis or septic shock on presentation (aOR, 2.39; 95% CI, 1.28–4.44), prior vancomycin exposure (aOR, 2.21; 95% CI, 1.13–4.30), and recent hospitalization within 3 months (aOR, 2.11; 95% CI; 1.01–4.40). All independent predictors had a value of one point. Youden's index statistics indicated a score of ≥3 as best cutoff value that had a sensitivity of 69.6% and specificity of 78.4%.ConclusionsSimple decision rule helps clinicians stratify the risk of high vancomycin MIC MRSA infection when deciding empirical therapy for patients with community-onset infections.