Outcome of Bloodstream Infections Caused by Antibiotic-Resistant Bacteria: A 7-Year Retrospective Study at the University Hospital of Palermo, Italy

Background: Bloodstream infections (BSIs) are both a primary cause and a severe complication of hospitalization. This retrospective study aims to analyze the epidemiology of BSIs at the University Hospital of Palermo from 2018 to 2024. Methods: We conducted a single-center, retrospective, observational study at the University Hospital Paolo Giaccone in Palermo, analyzing microbiological data from blood cultures collected between 1 January 2018 and 31 December 2024. Results: A total of 6345 blood culture isolates from 2967 patients were analyzed. Bacteremia-related mortality per 1000 patients rose from 5.1% in 2018 to 10.5% in 2024. The most isolated pathogens were non-aureus staphylococci (39.7%), followed by Klebsiella pneumoniae (12.1%) and Staphylococcus aureus (7.47%). Acinetobacter baumannii and Pseudomonas aeruginosa were more prevalent in ICUs. The number of K. pneumoniae, A. baumannii, S. aureus, and P. aeruginosa isolates per 1000 admitted patients increased significantly over time. Oxacillin resistance in S. aureus peaked at 49.0% in 2020 before declining, while among non-aureus staphylococci, it remained consistently high (>80%). Carbapenem-resistant K. pneumoniae peaked at 80% in 2022 before decreasing in 2024. Resistance to ceftazidime-avibactam and meropenem-vaborbactam was observed in 11.3% and 11.8% of K. pneumoniae, respectively. Multivariable analysis identified A. baumannii and K. pneumoniae BSIs as independent predictors of in-hospital mortality. Additionally, female sex, pneumonia, and central nervous system infections were significant risk factors for mortality. Conclusions: We observed an increasing trend in overall bacteremia-related mortality from 2018 to 2024. Microbiological data highlight the predominance of non-aureus staphylococci, K. pneumoniae, and S. aureus as leading pathogens of BSI, with A. baumannii emerging as a significant threat, particularly in ICUs. Rising antimicrobial resistance, especially among K. pneumoniae, underscores the urgent need for robust antimicrobial stewardship programs. K. pneumoniae and A. baumannii were associated with higher mortality.