Outbreak of Blastomycosis Among Paper Mill Workers — Michigan, November 2022–May 2023
2025

Blastomycosis Outbreak Among Paper Mill Workers in Michigan

Sample size: 645 publication Evidence: high

Author Information

Author(s): Harvey R. Reid, O’Connor Allyson W., Stanton Marcia L., Park Ju-Hyeong, Shi Dallas, Callaway Perri C., Liang Xiaoming, LeBouf Ryan, Bailey Rachel, Fechter-Leggett Ethan, Hennessee Ian, Toda Mitsuru, Reik Rebecca, Stobierski Mary Grace, McFadden Jevon, Palmer Sara, Millerick-May Melissa, Yin Robert, Snyder Michael, Meece Jennifer, Olstadt Jeremy, Sterkel Alana K., Dargle Suzanne, Bree Olivia, Weissman David, de Perio Marie A., Hines Stella, Cox-Ganser Jean

Primary Institution: Centers for Disease Control and Prevention

Conclusion

The outbreak of blastomycosis among paper mill workers in Michigan was the largest documented in the United States, with 162 cases identified.

Supporting Evidence

  • The outbreak involved 162 confirmed cases of blastomycosis among 645 workers.
  • Environmental sampling did not identify the source of Blastomyces exposure.
  • The outbreak was declared over on July 1, 2023, with no additional cases reported as of April 2024.
  • 12% of workers with blastomycosis were hospitalized during the outbreak.
  • The peak number of new cases occurred in early March 2023, with 21 cases reported in one week.

Takeaway

A lot of workers at a paper mill in Michigan got sick from a rare fungus called Blastomyces, and it was the biggest outbreak ever in the U.S. for this disease.

Methodology

The investigation included a medical survey and urine antigen testing among mill workers to identify cases of blastomycosis.

Potential Biases

Potential bias in self-reported diagnoses and the timing of medical surveys may affect results.

Limitations

Environmental sampling did not identify the source of Blastomyces exposure in the mill.

Participant Demographics

Majority of workers were men (83%), White (94%), and non-Hispanic (98%), with a median age of 46 years.

Statistical Information

P-Value

p<0.05

Statistical Significance

p<0.05

Digital Object Identifier (DOI)

10.15585/mmwr.mm735152a2

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