Marshfield Clinic Research Institute Investigates Samples From Blastomycosis Outbreak in Michigan

Tuesday, December 31st, 2024 -- 10:00 AM

Marshfield Clinic Research Institute tested nearly 500 environmental samples during the multi-state, multi-agency investigation into the largest known blastomycosis outbreak in the United States, which sickened workers at an Escanaba, Michigan paper mill and resulted in one death.

In March 2023, a cluster of atypical pneumonia cases, many of which were attributed to mill workers at the Billerud paper mill in Escanaba, was reported to the local health department.

Investigators from the Centers for Disease Control and Prevention’s (CDC) National Institute for Occupational Safety and Health (NIOSH), working with public health partners, facilitated blastomycosis case-finding through a medical survey and conducted an environmental assessment.

A survey of 645 mill workers showed that 162 people (25%) were identified with blastomycosis between Nov. 1, 2022, and May 15, 2023, according to a study published online Dec. 30 in the CDC's weekly Morbidity and Mortality Weekly Report.

Overall, an estimated 20% of workers at the paper mill in Michigan tested positive for blastomycosis. Blastomycosis is a rare infectious disease caused by inhalation of Blastomyces fungal spores from the environment.

Blastomyces is found in moist soil or decaying wood and leaves, often near rivers and lakes. Blastomycosis incubates over a two-week to three-month period and pulmonary illness is most common, ranging from mild, respiratory symptoms to severe, potentially fatal pneumonia.

Blastomycosis is an endemic and reportable disease in Michigan with 186 cases reported between 2007-2017. Blastomycosis does not spread from person to person.

Jennifer Meece, Ph.D., is the executive director of Marshfield Clinic Research Institute and has researched blastomycosis for more than 20 years, investigating outbreaks throughout the Midwest.

She said it’s critical to launch a comprehensive investigation as soon as possible when clusters of potential blastomycosis cases are reported. “Blastomycosis is difficult to diagnose because its symptoms often mimic other respiratory illnesses, like pneumonia, making it hard to distinguish clinically,” Meece said.

“Diagnosis requires seeing the fungus in tissue samples through a culture or microscope. It’s important for patients to begin treatment with antifungal medication as soon as possible, and to attempt to find the source of the exposure to prevent others from inhaling the spores.”

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