Mortality due to carbapenem-resistant Acinetobacter baumannii bacteraemia: a five-year cohort study in intensive care patients.

Abstract

Objectives: Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as a major and difficult-to-treat nosocomial pathogen. This study estimated the mortality associated with CRAB bacteraemia in patients receiving treatment in the intensive care unit. A susceptible-infection counterfactual framework was applied to reflect the potential benefit of improved antimicrobial therapy.

Methods: A five-year (2019-2023) cohort study was conducted in a tertiary-care referral hospital in Greece. Competing risks survival analysis methods were applied to estimate excess in-hospital mortality due to CRAB bacteraemia by comparing patients infected by CRAB to those infected by other more susceptible Gram-negative bacteria (GNB).

Results: The cohort comprised 400 intensive care patients with GNB bacteraemia (median age 70 years, 65% male). CRAB was the most common pathogen (43%), followed by K. pneumoniae (12%), E. coli (11%), and P. aeruginosa (10%). Patients with CRAB bacteraemia experienced significantly higher in-hospital mortality at 14 days (35% vs. 21%), 28 days (53% vs. 30%) and overall (74% vs. 52%) compared to patients with other GNB bacteraemia. Multivariable competing-risks regression confirmed that CRAB bacteraemia was independently associated with increased risk of 28-day inpatient death (cause-specific hazard ratio [csHR] 1.80, 95% CI 1.28-2.54; sub-distribution hazard ratio [sHR] 1.84, 95% CI 1.28-2.62), simultaneously lowering the probability of discharge alive (csHR 0.68, 95% CI 0.38-1.21; sHR 0.52, 95% CI 0.30-0.91). Estimation of the attributable fraction suggested that effective antimicrobial management may result in a relative decrease in the risk of in-hospital mortality by 44% (95% CI 22%-61%) in CRAB bacteraemia patients.

Conclusions: CRAB's detrimental role as a leading cause of increased inpatient mortality and prolongation of hospitalisation in intensive-care patients was demonstrated. These outcomes could improve substantially if more effective antimicrobial treatment becomes available. Nevertheless, considering CRAB is predominantly a hospital-acquired pathogen, efforts should always be directed towards preventing nosocomial transmission.