Epidemiological and Clinical Features of a Large Blastomycosis Outbreak at a Paper Mill in Michigan

Abstract

Background: Blastomycosis is an environmentally acquired fungal infection that can result in severe pulmonary illness and high hospitalization rates. In 2023, a blastomycosis outbreak was detected among workers at a paper mill in Delta County, Michigan. Methods: We included patients with clinical and laboratory evidence of blastomycosis who had spent ≥40 hours in Delta County since 1 September 2022 and had illness onset 1 December 2022-1 July 2023. We assessed epidemiological and clinical features of patients and evaluated factors associated with hospitalization. We performed whole-genome sequencing to characterize genetic relatedness of clinical isolates from 8 patients. Results: In total, 131 patients were identified; all had worked at or visited the mill. Sixteen patients (12%) were hospitalized; 1 died. Compared with nonhospitalized patients, more hospitalized patients had diabetes (P =. 03) and urine antigen titers above the lower limit of quantification (P