The comparator arm consists of 2g of meropenem given intravenously every 8 hours.Duration of therapy should follow local guidelines and de-escalation is allowed after identification of causative pathogens.

To demonstrate the non-inferiority of ceftolozane/tazobactam versus meropenem in participants with Febrile Neutropenia on Patients Colonized With or at Risk for Infection With Extended Spectrum Beta Lactamase - Producing Pathogens at the TOC visit (7 to 14 days after the end-of-therapy [EOT] visit) using a non-inferiority margin of 12.5%. Clinical response at the TOC visit was defined as cure (complete resolution of fever and symptoms related to Febrile Neutropenia), failure (non-resolution, relapse or recurrence of Febrile Neutropenia) or indeterminate (no evaluable study data). A favorable clinical response is a clinical cure. A missing clinical response will be considered indeterminate unless the clinical outcome at the EOT visit was failure.

The incidences of microbiologically documented infections, along with the identification of causative organisms in culture, will be recorded. The measure will be assessed through the counting of cases confirmed by positive cultures.

In-hospital mortality in the first 100 days after allogenic hematopoietic stem cell transplant (HSCT)

Occurrence of GVHD In the first 100 days after allogenic HSCT

Frequency of multidrug resistant-pathogen infections or colonization by weekly rectal swab screening

Patients will also undergo faecal microbiota analysis on baseline and at the end of therapy as a surrogate marker for future GVHD.

An AE is any untoward medical occurrence in a participant administered a pharmaceutical product that does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal product, whether or not related to the medicinal product.

A serious adverse event (SAE) is an AE that results in death, is life threatening, requires or prolongs an existing hospitalization, results in persistent or significant disability or incapacity, is a congenital anomaly or birth defect, or is another important medical event deemed such by medical or scientific judgment.

An AE is any untoward medical occurrence in a participant administered a pharmaceutical product that does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal product, whether or not related to the medicinal product.