Epidemiology of Carbapenem-Resistant Acinetobacter baumannii Bloodstream Infections in Poland: A Multi-Center Study of Mortality, Risk Factors and Drug Resistance

<b>Background</b>: <i>Acinetobacter baumannii</i> (AB), particularly carbapenem-resistant strains (CRAB), is a major cause of difficult-to-treat infections associated with substantial mortality. Contemporary data from Central and Eastern Europe remain scarce. We aimed to characterize the epidemiology, clinical features, and survival of patients with AB bloodstream infection in a multicenter Polish cohort. <b>Methods</b>: We conducted a retrospective multicenter study including consecutive adults with microbiologically confirmed AB bloodstream infection. Clinical and demographic data, comorbidities, infection origin, and antimicrobial treatments were collected. Outcomes included all-cause in-hospital mortality and infection-attributed mortality. Survival was assessed using Kaplan-Meier curves and log-rank tests, while factors associated with death were examined with univariable and multivariable Cox regression. <b>Results</b>: Among 245 patients with CRAB bloodstream infection, overall mortality was 69.4%, and infection-attributed mortality reached 51.8%. Most infections (75.1%) were hospital-acquired. In univariable analyses, male sex (HR = 0.66; <i>p</i> = 0.008) and colistin-based therapy (HR = 0.71; <i>p</i> = 0.037) were associated with improved survival. Conversely, hospital-acquired infection (HR = 0.43; <i>p</i> < 0.001) and acute kidney injury (HR = 1.40; <i>p</i> = 0.038) were linked to higher mortality. In the multivariable model, male sex remained protective (HR = 0.61; <i>p</i> = 0.006), while hospital-acquired infection (HR = 0.35; <i>p</i> < 0.001) and COVID-19 (HR = 1.64; <i>p</i> = 0.049) independently predicted death. After adjustment, no other comorbidities or antimicrobial regimens showed significant associations. <b>Conclusions</b>: In this multicenter cohort of patients with CRAB bloodstream infection, mortality remained extremely high. Hospital-acquired infection, acute kidney injury, and COVID-19 were strong independent predictors of poor outcomes, whereas male sex was associated with better survival. Although colistin-containing therapy appeared beneficial in univariable analysis, this effect did not persist after adjustment, underscoring potential confounding. These findings highlight the urgent need for early recognition, optimized antimicrobial strategies, and prevention of healthcare-associated spread to improve outcomes in CRAB bacteremia.