Mucormycosis outbreak caused by Rhizomucor pusillus in a Hematopoietic Stem Cell Transplant Unit, Brazil

Mucormycosis is a severe fungal infection with high mortality in immunocompromised patients. Although most cases occur sporadically in the community setting, there are reports of healthcare-associated outbreaks of mucormycosis. We describe the investigation and clinical features of an outbreak of mucormycosis caused by Rhizomucor pusillus in a hematopoietic stem cell transplant (HSCT) unit in Brazil. Cases were screened through the hospital records, defined according to the European Organization for Research and Treatment of Cancer and the Mycoses Study Group Education and Research Consortium criteria, and classified as HSCT unit-acquired or not. Mucormycosis incidence was monitored from 2 years before the index case until 2 years after the last case. The clinical course of identified cases and potential environmental exposure data were recorded. Microbiological samples were identified with conventional methods and internal transcribed spacer sequencing; whole genome sequencing was performed for phylogenetic analysis. Potential source investigation was conducted according to the US Centers for Disease Control recommendations. Four proven cases of HSCT-unit-acquired mucormycosis were identified over a 10-month period. Rhizomucor pusillus was identified in three of the four patients. Disseminated disease, beginning with pulmonary infection, was the most common clinical presentation. Survivors (75%) received treatment with lipid complex amphotericin B, isavuconazole, and/or surgical resection. Environmental investigation was negative and phylogenetic analysis demonstrated that isolates were not clonal. Following air system maintenance, no further cases were identified. We characterize the first reported outbreak investigation of mucormycosis caused by R. pusillus in a Brazilian HSCT unit, with favorable outcomes in most cases despite aggressive clinical presentation. Despite the lack of clonality and negative environmental investigation, epidemiological evidence strongly suggests nosocomial transmission.