Acquisition of carbapenem-resistant Gram-negative bacilli in intensive care unit: predictors and molecular epidemiology

We had for aim to determine the risk factors for acquiring carbapenem-intermediate or -resistant Gram-negative bacilli (CR-GNB) in an intensive care unit (ICU) and to identify the resistance mechanisms involved. We conducted an observational prospective cohort study during 6 months in medical and surgical ICUs of the Besançon Teaching Hospital. Patients with acquired CR-GNB were patients whose cultures (screening or diagnosis) became positive more than 48h after admission to the ICU. The risk factors for ICU-acquired CR-GNB were determined by multivariate logistic regression. CR-GNB isolates were typed by pulsed-field gel electrophoresis (PFGE) and screened for resistance mechanisms with phenotypic and genotypic tests. Twenty-three of the 347 included patients had acquired a CR-GNB. The multivariate analysis revealed significant associations between this acquisition and the duration of previous treatments with piperacillin-tazobactam (adjusted odds ratio [aOR], 1.13, P=0.02) and aminoglycosides (aOR, 1.62; P=0.005), but not with carbapenems. The CR-GNB strains were identified as Pseudomonas aeruginosa (n=10), Stenotrophomonas maltophilia (n=7), and Enterobacter cloacae (n=6). No acquired carbapenemase-producing strain was identified. PFGE typing identified 1 multiple clone among P. aeruginosa isolates (4 patients), whereas for the other bacteria, all the strains were different. Our study results suggest that the strategy to prevent the emergence and spread of CR-GNB should not be limited to the sole restriction of carbapenem use in ICU settings.