ESCANABA, Mich. (From news release) - The CDC released a new report on the largest known blastomycosis outbreak in the United States, which happened at a Michigan paper mill and led to one death.

Between Nov. 1, 2022, and May 15, 2023, 162 mill workers were identified with blastomycosis. They worked at the Billerud paper mill in Escanaba. Overall, an estimated 20% of workers at the paper mill in Michigan tested positive for blastomycosis, the report said. One person died.

Blastomycosis is a rare infectious disease caused by inhaling Blastomyces fungal spores from the environment. Blastomyces are found in moist soil or decaying wood and leaves, often near rivers and lakes. People infected experience symptoms ranging from mild, respiratory issues to severe, potentially fatal pneumonia.

Blastomycosis is an endemic and reportable disease in Michigan with 186 cases reported between 2007-2017, according to the Marshfield Clinic Research Institute. Blastomycosis does not spread from person to person.

The Marshfield Clinic Research Institute led the lab testing for the investigation into the paper mill outbreak.

In addition to being the largest blastomycosis outbreak ever reported in the U.S., this was the first associated with a paper mill or other industrial worksite. The mill's location along a riverway in a wooded environment is consistent with Blastomyces habitat.

Blastomyces typically does not propagate indoors; the spores potentially entered the building through unfiltered ventilation systems, open doors, and caused the exposure over several months, the Marshfield Clinic Research Institute reported Monday.

Marshfield Clinic Research Institute and the Wisconsin State Laboratory of Hygiene analyzed environmental samples for Blastomyces.

Environmental samples collected included soil, wood chips, indoor surface dust, and water, dust, duct lining and filters from HVAC systems. Among 533 indoor and outdoor samples analyzed, no Blastomyces was detected and the specific environmental factors in or around the mill that led to this outbreak remain unknown.

"This was not an unexpected outcome as Blastomyces is an elusive organism," said Jennifer Meece, Ph.D., who is the executive director of Marshfield Clinic Research Institute. "It is rare, if not unheard of, that the exact source of a blastomycosis outbreak has ever been detected in the environment."

While many people who recreate in areas where blastomycosis is endemic are aware of the disease, this first-time outbreak at an industrial business opens new potential risks for exposure, the Marshfield Clinic Research Institute said in Monday's news release.

Health care providers and public health authorities should consider work-related exposure to Blastomyces to detect future outbreaks and implement public health interventions quickly, officials said. Industries with workers who routinely work outdoors in the midwestern and southeastern United States should consider providing worker training and education to enhance awareness of Blastomyces.