Abstract
Invasive infections caused by Magnusiomyces spp. are rare, but are associated with severe complications in hematopoietic cell transplantation (HCT) recipients and hospital outbreaks. Following a Magnusiomyces clavatus outbreak in our HCT unit, a prospective targeted screening protocol was implemented, which included pharyngeal and rectal swabs cultured on yeast-selective media with prolonged incubation. Clinical and microbiological data were analyzed, and whole-genome sequencing (WGS) was performed on the available isolates. During the study period (September 2022-July 2023), five colonizations and five invasive breakthrough Magnusiomyces infections were identified. Despite prompt initiation of antifungal treatment, 4/5 patients (80%) died. WGS demonstrated clonal relatedness among four M. clavatus isolates, supporting clonal transmission, although no environmental sources were identified. An enhanced two-phase screening strategy involving 71 patients showed limited benefit, identifying only one additional colonization case compared to routine surveillance cultures. A retrospective review (2007-2021) identified 58 Magnusiomyces spp. episodes, with only 10% occurring in patients with hematological malignancies. Our study describes a prolonged clonal outbreak confined to an HCT unit and provides a detailed evaluation of a targeted screening approach in this setting, highlighting the challenges of early identification and prediction of invasive infections. Further studies are needed to define the optimal surveillance and prevention strategies.