Risk Factors of Blood Culture Positivity and Mortality in Bloodstream Infections: A Population‐Based Study of Patients With B‐Cell Malignancies

Background Bloodstream infections remain a major cause of mortality among cancer patients. Pathogen surveillance and risk stratification tools are key to improved management. This study describes trends in causative pathogens and explores risk factors for positive blood cultures (PBCs) and post‐infection mortality in cancer patients. Methods We performed a cohort study of patients diagnosed with a B‐cell malignancy in the North Denmark Region between 2013 and 2022, linking cancer registry data to health records. Causative pathogens were described. LASSO regression was used to select variables associated with PBCs and post‐infection mortality. Odds ratios were estimated by univariate analyses. Results Among 1592 patients with B‐cell malignancies, 341 patients (21.4%) had at least one PBC, yielding 484 PBCs. We observed a shift from Gram‐positive to Gram‐negative dominance, driven by an increased frequency of the most common pathogen Escherichia coli (24.8%). Patients with neutropenia, elevated CRP, sepsis, hypotension, or kidney failure had a higher risk of a PBC. Advanced age, kidney failure, and sepsis were all associated with 30‐ and 90‐day post‐infection mortality. Conclusion Routinely available parameters obtained at time of admission were associated with blood culture positivity and mortality. Our findings support the rationale for developing predictive models to individualise infection management.