Bloodstream infections caused by multidrug-resistant organisms in patients with and without cancer: clinical outcomes and resistance determinants in a southern Italian cohort

Background Bloodstream infections (BSIs) due to multidrug-resistant organisms (MDROs) are associated with high morbidity and mortality, especially in patients with cancer, who often have immune dysfunction, frequent healthcare exposure, central venous catheters, prior antimicrobial therapy, and disease-related frailty. We compared clinical characteristics, resistance profiles, microbiology, and outcomes of MDRO BSIs in oncologic and non-oncologic patients hospitalized at the Policlinico of Bari. Methods We conducted a retrospective cohort study of hospitalized patients with MDRO BSIs from 1 January 2021 to 30 January 2026. Patients were classified as oncologic or non-oncologic according to the presence of solid tumors or haematologic malignancies. Demographic, clinical, microbiological, molecular, treatment-exposure, and outcome data were compared between groups. Resistance determinants were categorized as KPC, NDM, VIM, or other/undetermined, when available. MDR/carbapenem-resistant Acinetobacter spp. was analysed as a distinct high-risk phenotype. The primary outcome was 30-day all-cause mortality. Kaplan–Meier analysis and logistic regression were used to assess survival and mortality predictors. Results Overall, 204 patients were included: 145 non-oncologic and 59 oncologic patients, including 30 with solid tumors and 29 with haematologic malignancies. ICU admission at BSI onset was more frequent in oncologic patients (25.4% vs. 4.8%, p < 0.001). KPC-producing Enterobacterales were the leading resistance determinant (147/204, 72.1%), followed by MDR/carbapenem-resistant Acinetobacter spp. (35/204, 17.2%), NDMproducing Enterobacterales (14/204, 6.9%), and VIM-producing Enterobacterales (6/204, 2.9%). MDR/carbapenem-resistant Acinetobacter spp. was more common among oncologic patients, although not significantly (25.4%vs. 13.8%, p = 0.07). Seven-day mortality did not differ significantly (13.6% vs. 8.3%, p = 0.30), whereas 30-day mortality was higher among oncologic patients (30.5% vs. 11.7%, p = 0.002). Kaplan–Meier analysis confirmed reduced 30-day survival in oncologic patients (log-rank p = 0.020). In multivariable analysis, oncologic status (aOR 3.19, 95% CI 1.92–5.21, p = 0.010) and MDR/carbapenem-resistant Acinetobacter spp. BSI (aOR 2.41, 95% CI 1.12–5.18, p = 0.020) were independently associated with mortality. Conclusions Oncologic patients with MDRO BSIs experienced significantly higher 30-day mortality. These findings suggest that outcomes after MDR bloodstream infection are associated with the interplay of host vulnerability, oncologic status, comorbidity burden, and molecular or microbiological resistance profiles, particularly MDR/carbapenem-resistant Acinetobacter spp.