Pneumonia definition in allogeneic hematopoietic cell transplant recipients: Update and challenges in 2024. Recommendations from the EBMT Infectious Diseases Working Party and Practice Harmonization and Guidelines committee

To optimize and homogenize data on infectious diseases complications, the Infectious Diseases Working Party of the European Society for Blood and Marrow Transplantation (IDWP EBMT) participated in the 2023 EBMT international workshop focusing on the standardization of the definition of specific infections, including respiratory infections [1]. This is pertinent considering that a new software for data collection, including data on post-transplant infectious disease complications, was launched in 2023 and which will remain the main tool for future epidemiological studies. In this report, we briefly discuss our proposals for pneumonia definition, predominately focusing on bacterial and fungal pneumonias. We specifically address definitions of pneumonia diagnosis, infection onset date, resolution, recurrence, and breakthrough infection, and the challenges we encountered as a group to accurately define pneumonia in hematopoietic cell transplant (HCT) recipients (Table 1). Infections with community acquired respiratory viruses and adenovirus are discussed in a separate report [1]. Definitions on CMV pneumonia have been previously described and recently updated and hence not discussed in this paper [2,3].