Incidence, Risk Factors, and Outcomes of Bloodstream Infection during Conditioning Phase before Allogeneic Hematopoietic Stem Cell Transplantation.

Bloodstream infections (BSI) pose critical risks during allogeneic hematopoietic stem cell transplantation (allo-HSCT), yet data on BSI during the conditioning phase remain limited. To assess the characteristics, risk factors, and outcomes of BSI during conditioning in allo-HSCT patients with hematological diseases. We conducted a single-center retrospective cohort study including 2395 consecutive allo-HSCT recipients between September 2013 and September 2023. BSI occurred in 113 patients (5.7% cumulative incidence), with median onset on day -2. Monomicrobial Gram-negative bacteria (73.5%, 83/113) and Gram-positive bacteria (18.6%, 21/113) predominated, with polymicrobial BSI in 8.0% (9/113). Carbapenem-resistant Gram-negative organisms (CRO) constituted 15.9% (18/113) of infections. Independent BSI risk factors included antithymocyte globulin (ATG)-mediated conditioning (96.5% of BSI cases), aplastic anemia (AA), hematopoietic cell transplantation-comorbidity index (HCT-CI) ≥2, and preconditioning neutropenia ≥7 days. Patients were stratified by risk based on cumulative incidence: low (0 factor ± ATG, 3.3%), intermediate (ATG + 1 factor, 9.3%), and high (ATG + ≥ 2 factors, 21.4%) (P < .001). BSI significantly reduced 28-day survival (94.7% versus 99.7%, P < .001), with 5.3% mortality (6/113). CRO BSI exhibited lower survival than non-CRO cases (76.5% versus 97.9%, P < .001). Prior CRO colonization independently predicted CRO BSI (P = .003). Appropriate empirical therapy and ceftazidime/avibactam (CAZ-AVI)-based definitive regimens improved early survival. BSI surveillance should prioritize patients undergoing ATG-based conditioning, particularly those with AA, HCT-CI ≥ 2, or preconditioning neutropenia ≥7 days. Given the dominant mortality risk of CRO BSI during conditioning, pre-HSCT CRO screening is imperative, and targeted therapies such as CAZ-AVI are critical.