Clinical and microbiological characteristics of polymicrobial bloodstream infections in hematologic malignancy patients: a cross-sectional study

Patients with hematological malignancies experience severe immune dysfunction due to the impact of intensive chemotherapy and the impairment of hematopoietic cells. This condition places them at high risk for infectious complications, including bloodstream infections (BSIs), which are associated with increased morbidity and mortality. Polymicrobial bloodstream infections (PBSIs), involving multiple microorganisms, represent a critical clinical condition with high mortality rates in this population. This study aimed to investigate the risk factors for poor clinical outcomes associated with PBSIs in patients with severe immunodeficiency due to hematological malignancies and to propose potential solutions. A retrospective review was conducted on the medical records of patients diagnosed with bloodstream infections at Muğla Education and Research Hospital between 2017 and 2024. Data on demographics, laboratory results, microbiological isolates, antibiotic susceptibility profiles, and mortality outcomes were analyzed. High-risk conditions for PBSI were identified. PBSI was defined as the isolation of two or more bacterial species from blood cultures within 72 h of infection onset. A total of 108 patients were included, of whom 21 (19.4%) were diagnosed with PBSI. The most common pathogens were coagulase-negative staphylococci, Klebsiella spp., and Pseudomonas aeruginosa. Multidrug-resistant (MDR) organisms were identified in 58.3% of cases, and the mortality rate in PBSI patients was 57.1%. Risk factors for mortality included intensive care unit admission, mechanical ventilation, parenteral nutrition, renal failure, and concurrent pneumonia. PBSIs are a significant cause of morbidity and mortality in patients with hematological malignancies undergoing chemotherapy. To mitigate the effects of identified risk factors, measures such as avoiding unnecessary intensive care admissions, minimizing catheter and mechanical ventilation use, prioritizing enteral over parenteral nutrition, and initiating broad-spectrum antibiotics promptly are recommended. Multicenter, randomized, prospective studies are essential to optimize treatment strategies and reduce PBSI-associated mortality in this vulnerable patient group.