The goals of this observational study are to identify risk factors for ESBL-producing Enterobacterales and carbapenemase-producing Enterobacterales (CPE) colonization in oncohematological patients with severe neutropenia, and to develop and validate a predictive model of infection caused by ESBL-producing Enterobacterales and CPE in patients previously colonized by the same bacteria.

The main questions the study aims to answer are:

• What are the risk factors for ESBL-producing Enterobacterales and CPE colonization in patients with severe neutropenia?
• Can a predictive model be developed to accurately predict infections in the colonized patients?

Study Design & Participants: Participants will be screened after receiving neutropenia-inducing treatment (e.g., chemotherapy, chimeric antigen receptor T-cell (CAR-T) therapy, or others). A baseline rectal swab will be collected to assess initial colonization status, followed by weekly swabs throughout the duration of neutropenia. Patients will be followed for 90 days from initial screening, during which the study team will record any infections, with an additional 30-day follow-up period. All hospitalization data will be recorded.

An exploratory metagenomics sub-study will be conducted within the study. Its goal is to describe the intestinal microbiome in patients and analyze any correlation between the microbiome and infection and mortality. For logistical reasons, this sub-study will be performed only on patients in the Seville area. This analysis will be performed via sequencing of the 16S ribosomal ribonucleic acid (rRNA) gene.

Inclusion criteria

• Patients admitted to Hematology departments with hematological diseases, including: myelodysplastic syndrome, acute myeloid leukemia, acute lymphoblastic leukemia, multiple myeloma, chronic lymphocytic leukemia, chronic myeloproliferative leukemias, lymphomas, or other hematological disorders.
• Patients scheduled to receive treatment for their underlying hematological disease, including myeloablative/cytotoxic chemotherapy, conditioning chemotherapy for hematopoietic stem cell transplantation (autologous, allogeneic, or other types), lymphodepleting chemotherapy for CAR-T cell therapy, and/or other treatments expected to induce neutropenia.
• Patients expected to develop neutropenia (neutrophil count < 0.5 \times 10^9/L, or < 1.0 \times 10^9/L when predicted to fall below 0.5 \times 10^9/L within the next 48 hours) in the coming days.
• Those who have signed the informed consent form.
• Participation in another study is permitted, provided it is observational and does not influence the potential colonization status.

Exclusion criteria

• Psychiatric disorder or inability to understand or follow the protocol instructions.
• Terminally ill patients or those with an estimated life expectancy of less than 30 days.
• Previous enrollment in the study.
• Known prior colonization by ESBL-producing Enterobacteriaceae (ESBL-E) or carbapenemase-producing Enterobacteriaceae (CPE).
• Physician's discretion: The patient's attending physician prefers not to include the patient in the study.

Patients with hematological diseases, including: myelodysplastic syndrome, acute myeloid leukemia, acute lymphoblastic leukemia, multiple myeloma, chronic lymphocytic leukemia, chronic myeloproliferative leukemias, lymphomas, or other hematological disorders.