The Billirud Mill Blastomycosis Outbreak: Comparison to Historical Controls

Area of Science:

• Infectious Diseases
• Epidemiology
• Mycology

Background:

• Blastomycosis is a fungal infection endemic in certain regions.
• An unusual outbreak of blastomycosis was identified among paper mill workers in Escanaba, Michigan.
• This outbreak presented unique characteristics compared to historical data.

Purpose of the Study:

• To analyze the characteristics of a large blastomycosis outbreak in paper mill workers.
• To compare outbreak cases with historical blastomycosis data in the Upper Peninsula of Michigan.
• To identify risk factors and potential sources of infection within an industrial setting.

Main Methods:

• Utilized the Michigan Disease Surveillance System for descriptive and outcome data (2007-2023).
• Estimated baseline regional blastomycosis incidence.
• Employed quantitative methods (t-tests, chi-square, regression) to compare outbreak cases with historic controls.

Main Results:

• The outbreak involved 120 cases (28 confirmed, 92 probable) of blastomycosis.
• Outbreak cases were significantly younger, more male, and reported more respiratory symptoms.
• A shorter time from illness onset to diagnosis was observed in outbreak cases.
• This outbreak was the largest reported, the first in an industrial facility, and the first involving Blastomyces gilchristii.

Conclusions:

• The Billirud paper mill outbreak is a significant event in blastomycosis epidemiology.
• Industrial facilities handling forestry products may be at risk due to endemic Blastomyces species.
• Further investigation into environmental and occupational exposures is warranted.