Mortality impact of carbapenem-resistant Acinetobacter baumannii (CRAB) colonization and infection: a retrospective cohort study

Background: The clinical impact of carbapenem-resistant Acinetobacter baumannii (CRAB) remains controversial, with uncertainty about whether it directly contributes to mortality or merely reflects underlying patient’s morbidity. This study aimed to evaluate the impact of CRAB colonization and infection on patient outcomes. Methods: A retrospective cohort study was conducted in an Israeli tertiary hospital between January 2023 and December 2024. Patients were categorized into CRAB-negative (A group), CRAB-present on admission (POA, B group), and hospital-acquired CRAB (C group). Time-varying Cox proportional hazards models were used to estimate 30- and 90-day mortality risks while adjusting for immortal time bias. Kaplan–Meier and cumulative hazard curves were generated, and univariable Firth logistic regressions were performed as exploratory analyses. Results: Of 3,080 patients, 149 had CRAB-POA and 108 acquired CRAB. Risk factors for CRAB-POA included long-term care facility residence (odds ratio (OR) = 4.1) and mechanical ventilation (OR = 2.3). Hospital-acquired CRAB was associated with longer length of stay and ventilation. Time-varying Cox models adjusting for immortal time bias showed that both CRAB colonization and infection were associated with increased 30-day mortality (hazard ratio (HR) range: 1.95–2.88) and 90-day mortality (HR range: 2.11–2.93), compared with CRAB-negative patients. Implementation of enhanced screening and cohorting in the late study period was associated with reduced CRAB acquisition (OR = 0.13, 95% confidence interval (CI): 0.07–0.24) and mortality (OR = 0.62, 95% CI: 0.41–0.94). Conclusions: Both CRAB colonization and infection are associated with twofold increase in mortality after adjusting for disease severity. Enhanced infection control measures reduced acquisition and mortality.