Clinical Severity and Organ Dysfunction as Drivers of Mortality in Antimicrobial-Resistant Acinetobacter baumannii Pneumonia: A Retrospective Cohort Study

Background/Objectives: Acinetobacter baumannii is a major cause of hospital-acquired and ventilator-associated pneumonia and is associated with high mortality among critically ill patients. Although antimicrobial resistance remains a major therapeutic challenge, the relative contribution of clinical severity, organ dysfunction, and laboratory parameters to patient outcomes requires further clarification. Methods: We conducted a retrospective single-center cohort study including 165 patients with microbiologically confirmed A. baumannii pneumonia admitted to the Clinical Hospital of Pneumology Iași, Romania, between 2019 and 2025. Clinical, laboratory, and outcome data were analyzed, and multivariable logistic regression was performed to identify independent predictors of in-hospital mortality. Results: In-hospital mortality was independently associated with older age (OR: 1.05 per year, 95% CI: 1.01–1.08, p = 0.005), sepsis (OR: 5.23, 95% CI: 1.93–16.5, p = 0.002), and mechanical ventilation (OR: 6.71, 95% CI: 3.02–15.6, p < 0.001). In exploratory analyses restricted to patients with available lactate measurements, lactate levels were not significantly associated with mortality, whereas acute kidney injury and dynamic renal deterioration were associated with increased mortality. Inflammatory markers, particularly neutrophil-to-lymphocyte ratio and C-reactive protein at 72 h, were significantly higher in non-survivors. Conclusions: These findings suggest that mortality in A. baumannii pneumonia is more closely associated with clinical severity, sepsis, respiratory failure, and evolving organ dysfunction than with isolated laboratory parameters. Early recognition of sepsis, acute kidney injury, and respiratory failure, together with serial assessment of inflammatory biomarkers, may support improved risk stratification in this high-risk population.