Bloodstream Infections in Solid Malignancies: Risk Factors, Resistance Patterns, and Clinical Outcomes from a Two-Center Cohort in Heraklion, Crete

Background: Bloodstream infections (BSIs) represent a severe complication among patients with solid tumors (STs), contributing substantially to morbidity and mortality, especially in the context of increasing antimicrobial resistance (AMR). Evidence in STs remains limited compared to hematologic malignancies. Methods: We conducted a two-center observational study including 282 hospitalized adults with solid malignancies and documented infections; 66 patients (23.4%) had confirmed BSIs. Clinical characteristics, microbiological profiles, resistance patterns, and outcomes were evaluated. Results: Patients had a mean age of 66.4 ± 11.8 years, and 63.6% were male. The majority (84.8%) had stage IV disease and were receiving chemotherapy (95.5%). Gram-negative bacteria predominated (51.5%), mainly Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Multidrug resistance (MDR) was detected in 45.5% of isolates, while 28.8% of BSIs were polymicrobial; both were associated with worse outcomes and increased infection-related mortality (p = 0.041 and p = 0.032, respectively). Overall infection-related mortality reached 28.8%. In multivariable analysis, poor functional status (ECOG PS ≥ 2), prior hospitalization, and concurrent radiotherapy were independently associated with unfavorable outcomes. Conclusions: BSIs remain a significant cause of morbidity and mortality in patients with STs. The high burden of Gram-negative and MDR pathogens, along with the impact of polymicrobial infections and impaired performance status, highlights the need for early risk stratification and locally adapted empirical antimicrobial strategies. Prospective multicenter studies are warranted to validate these findings and optimize management strategies in this vulnerable population.