Rectal Colonization with Multidrug-Resistant Organisms and Subsequent Bloodstream Infections in Hematological Patients Undergoing Cellular Therapies.

Bacterial infections, especially bloodstream infections (BSIs), compromise the overall survival of patients with hematological malignancies undergoing cellular therapies. The interplay between rectal colonization by different types of multidrug-resistant organisms (MDRO) and subsequent BSIs is not fully determined. We aimed to describe the natural history and risk factors for colonization by MDRO, as well as its impact on subsequent BSIs in patients treated with cellular therapies in an environment of antimicrobial resistance. Retrospective, single-center cohort study of consecutive adult hematological malignancies patients treated with allogeneic or autologous hematopoietic cell transplantation (HCT) or chimeric antigen receptor T-cell therapy between 2021 and 2024 in Attikon University Hospital (Greece), with ≥1 available rectal screening test for carbapenem-resistant gram-negative bacilli (CR-GNB) and vancomycin-resistant Enterococcus faecium (VRE). Univariate and multivariate Cox regression were implemented for identifying predictors of CR-GNB and VRE colonization. We also studied the concordance between rectal colonization and subsequent BSIs. One hundred eighty-two patients were included (male: 64%, mean age: 50.2 ± 13 yr, acute myeloid leukemia/myelodysplastic syndrome diagnosis: 55%, relapsing/refractory disease: 58%, allogeneic HCT: 85%). Median duration of hospitalization and neutropenia was 35 and 15 d, respectively. At baseline, 95% of patients were negative on rectal screening for both CR-GNB and VRE, and of those, 8.4% and 23% were colonized with CR-GNB and VRE during follow-up, respectively. Prior colonization with the same pathogen was independently associated with subsequent CR-GNB (HR: 13.0, 95% CI: 2.83 to 59.3) and VRE (HR: 4.83, 95% CI: 2.28 to 10.2) colonization. Seventy-nine patients had ≥1 BSIs (gram-positive: 60%, gram-negative: 38%), with three concordant CR-GNB BSIs among 16 colonized patients (18.7%) and two CR-GNB BSIs among 153 noncolonized patients (1.3%). Regarding VRE, we identified two concordant BSIs among 45 colonized patients (4.4%). Despite the high MDRO prevalence, we observed low rates of CR-GNB colonization in neutropenic patients treated with cellular therapies, with one patient out of five experiencing a concordant CR-GNB BSI. VRE colonization was more frequent, but it rarely resulted in a concordant BSI. These findings highlight the importance of infection control strategies and support de-escalation approaches in empirical antibacterial treatment of febrile neutropenia in this vulnerable population.