Multicenter Study of the Relationship between Carbapenem MIC Values and Clinical Outcome of Patients with Acinetobacter Bacteremia.

The Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) offer different recommendations for carbapenem MIC susceptibility breakpoints for Acinetobacter species. In addition, the clinical efficacy of the intermediate category remains uncertain. This study was designed to determine the optimal predictive breakpoints based on the survival of patients with Acinetobacter bacteremia treated with a carbapenem. We analyzed the 30-day mortality rates of 224 adults who received initial carbapenem monotherapy for the treatment of Acinetobacter bacteremia at 4 medical centers over a 5-year period, according to the carbapenem MICs of the initial isolates. The 30-day mortality was about 2-fold greater in patients whose isolates had carbapenem MICs of ≥8 mg/liter than in those with isolates with MICs of ≤4 mg/liter. The differences were significant by bivariate analysis (53.1% [60/113] versus 25.2% [28/111], respectively; P < 0.001) and on survival analysis by the log rank test (P < 0.001). Classification and regression tree analysis revealed a split between MICs of 4 and 8 mg/liter and predicted the same difference in mortality, with a P value of <0.001. Carbapenem treatment for Acinetobacter bacteremia caused by isolates with carbapenem MICs of ≥8 mg/liter was an independent predictor of 30-day mortality (odds ratio, 4.218; 95% confidence interval, 2.213 to 8.039; P < 0.001). This study revealed that patients with Acinetobacter bacteremia treated with a carbapenem had a more favorable outcome when the carbapenem MICs of their isolates were ≤4 mg/liter than those with MICs of ≥8 mg/liter.