On Feb. 28, 2023, Public Health Delta & Menominee Counties (PHDM) was alerted to three cases of atypical pneumonia (suspected to be blastomycosis) in employees of a large paper mill in Escanaba, Michigan. On March 6, 2023, PHDM sent out a notice to local healthcare providers, noting eight blastomycosis cases under investigation, all male paper mill employees. Mill management sent out a
notice to all employees on March 10.

The Michigan Department of Health and Human Services (MDHHS) subsequently reported a cluster of blastomycosis cases among paper mill workers to the U.S. Centers for Disease Control and Prevention. An assessment of 645 mill workers identified 162 cases of blastomycosis with illness onset during November 1, 2022–May 15, 2023, with the weekly case count peaking at 21 cases in early March 2023.

Blastomycosis is a rare fungal disease often initially misdiagnosed, which can contribute to severe pulmonary illness. Community outbreaks have been reported after soil disruption and outdoor recreational activities in blastomycosis-endemic areas. Blastomyces lives throughout the Midwest, especially around the Ohio and Mississippi River valleys, the Great Lakes and the Saint Lawrence River. This was the first recognized blastomycosis outbreak in an industrial, largely indoor setting.