NDM-Producing Klebsiella pneumoniae Bloodstream Infection Increases Mortality and Impairs Hematopoietic Recovery in Acute Leukemia

Background: Bloodstream infections (BSIs) remain among the most serious complications of intensive chemotherapy for acute leukemia. Infections caused by New Delhi metallo-β-lactamase (NDM)-producing Klebsiella pneumoniae are associated with limited therapeutic options and poor prognosis; however, their impact on hematopoietic recovery has not been comprehensively evaluated. We investigated the association of NDM-producing K. pneumoniae BSI with mortality and hematopoietic recovery in patients with acute leukemia. Methods: This retrospective single-center cohort study included 255 microbiologically documented BSI episodes occurring in 201 adult patients with acute myeloid leukemia or acute lymphoblastic leukemia between January 2020 and December 2025. Episodes in the NDM group (n = 103) were compared with BSIs caused by other bacterial or fungal pathogens (n = 152). The primary endpoint was all-cause mortality. Secondary endpoints included the proportion achieving neutrophil and reticulocyte recovery, the cumulative incidence of neutrophil recovery, time to hematopoietic recovery among patients who survived and achieved recovery, and septic shock. Neutrophil recovery was additionally evaluated using a competing-risk approach, with death before recovery treated as a competing event. Independent predictors of mortality were identified using multivariable logistic regression. Results: Patients in the NDM group experienced significantly higher mortality than those in the comparator group (36.9% vs. 12.5%; OR 4.09, 95% CI 2.19–7.65; p < 0.001). Neutrophil recovery was achieved less frequently in the NDM group (63.1% vs. 87.5%; OR 0.24, 95% CI 0.13–0.46; p < 0.001). Among patients who survived and achieved hematopoietic recovery, the median time to neutrophil recovery was shorter in the NDM group (9 vs. 15 days; p < 0.001), an observation interpreted in the context of survivorship bias rather than accelerated marrow regeneration. The competing-risk analysis similarly demonstrated a lower cumulative probability of neutrophil recovery in the NDM group when death before recovery was considered as a competing event. Multivariable analysis identified NDM-producing K. pneumoniae BSI (adjusted OR 6.03, 95% CI 3.06–11.87), increasing age (adjusted OR 1.04 per year, 95% CI 1.01–1.06), and septic shock (adjusted OR 3.84, 95% CI 1.94–7.60) as independent predictors of mortality. Conclusions: NDM-producing K. pneumoniae bloodstream infection was independently associated with substantially increased mortality and a markedly reduced probability of hematopoietic recovery in patients with acute leukemia. The apparently shorter recovery time among patients who survived and achieved recovery should be interpreted in the context of selective early mortality rather than faster marrow regeneration. Assessment of severe bloodstream infections in acute leukemia should therefore integrate survival and hematopoietic recovery and account for death before recovery as a competing event.