How do Definitions for Nosocomial Invasive Aspergillosis Perform in Hematopoietic Cell Transplant Recipients?

Abstract

Invasive aspergillosis (IA) remains a major cause of morbidity and mortality among hematopoietic cell transplant (HCT) recipients, despite the use of protective environments and antifungal prophylaxis, raising ongoing concerns on the potential for nosocomial acquisition. We conducted a retrospective, single-center cohort study of adult allogeneic HCT recipients diagnosed with probable or proven IA between March 2021 and July 2025. Cases were classified as nosocomial (nIA) or community-acquired (cIA) using a cutoff of >14 days versus ≤14 days from hospital admission, respectively, with secondary analyses applying alternative definitions. Among 40 IA cases identified, 18 (45%) were classified as nIA using 14-day cutoff, while alternative definitions classified up to 70% of the cases as nosocomial. The proportion of IA cases classified as nosocomial varies substantially depending on the definition used, highlighting the limitations of criteria based on temporality alone. A more comprehensive, risk-based approach that incorporates host immunity, outpatient and inpatient environment and microbiologic factors in real time are needed to better define nosocomial IA and guide infection prevention strategies.