Between November 1, 2022 and May 15, 2023, paper mill workers in Michigan were part of the largest blastomycosis outbreak in US history, with 162 cases of the fungal disease identified among 645 mill workers.
This outbreak was the largest documented blastomycosis outbreak in the United States, and the first associated with a paper mill or an industrial setting.
“This outbreak was the largest documented blastomycosis outbreak in the United States, and the first associated with a paper mill or an industrial setting,” the authors said. Though rare, fungal infections are usually linked to inhaled spore exposure from moist soil or decaying wood and leaves in the midwestern and southeastern United States.
Officials learned of the outbreak at the end of February 2023, when Public Health Delta and Menominee Counties (PHDM) in Michigan was alerted to several atypical pneumonia cases among workers at a local paper mill in Delta County, Michigan. Patients experienced onset of respiratory symptoms during January and February of 2023, and urine samples were positive for Blastomyces.
The team published the findings yesterday in the latest issue of Morbidity and Mortality Weekly Report.
One death, 18 hospitalized
The majority of workers were men (83%), White (94%), and non-Hispanic (98%), with a median age of 46 years, the authors said. Ninety percent of patients who were positive for infection had a cough, 76% had both shortness of breath and fatigue, 73% had fever, and 63% had abnormal lung findings on chest imaging.
Eighteen (12%) workers with blastomycosis were hospitalized, and one patient died. Medical surveys were conducted among all plant workers, and officials estimated blastomycosis case prevalence was 20%.
Environmental samples were collected from the mill, surrounding forest, river, and outbuildings. “The mill’s location along a riverway in a wooded area is consistent with Blastomyces’ habitat, however, the specific environmental factors in or around the mill that led to this outbreak remain unknown,” the authors said.
