Targeted Screening to Predict Magnusiomyces Infections in Hematopoietic Cell Transplant Recipients: Evidence from an Outbreak Setting

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.