At least one person has died, and 96 others have been sickened, in an outbreak of blastomycosis at a northwest Michigan paper mill, local health authorities confirmed Friday. Federal investigators are preparing to step up their probe into this unprecedented number of typically rare and potentially deadly fungal infections.

The latest tally by Public Health Delta & Menominee Counties in the outbreak linked to the Escanaba Billerud Paper Mill includes 21 confirmed cases, where labs have been able to spot the fungus in samples collected from people with symptoms. An additional 76 cases are considered “probable,” with those people having showed symptoms and tested positive in an antibody or antigen test. 

A contractor who worked at the mill died after being diagnosed with blastomycosis, the health department said. His name was not immediately released.  

At least 12 people have been hospitalized.

All cases are among workers, contractors or visitors of a paper and packaging materials plant in the Michigan town of Escanaba, which is now temporarily shuttered by its owner, Billerud, in order to address the unprecedented outbreak.

“Everyone at Billerud is deeply saddened by this news,” said Brian Peterson, Billerud operations vice president for the mill, in a statement shared by the local health department. 

“Anyone who works at our facility is part of our team, and we are keeping this individual, their family, coworkers and friends in our thoughts and close to our hearts,” Peterson added.

Blastomycosis cases have been reported sporadically throughout North America, from the Midwest to the Southeast. A total of 240 cases were reported to the U.S. Centers for Disease Control and Prevention in 2019 nationwide. Only 26 cases are reported across Michigan on average each year, according to Public Health Delta & Menominee Counties.

Investigators from the CDC’s National Institute for Occupational Safety and Health (NIOSH) first visited the plant last month at the request of Billerud’s management. The team plans to return April 20 through April 29, an agency spokesperson said.

Around half of people develop symptoms after inhaling spores of the fungus Blastomyces, the CDC says, which often begin with common respiratory illness issues like fever, fatigue, and a cough. 

People are often infected after being exposed to moist soil or decaying wood and leaves where the fungus thrives. 

The CDC reported last month on an outbreak in a handful of Wisconsin neighborhoods that sickened four residents, one of whom died, and also sickened several pets. The outbreak may have been the result of construction kicking up spores.

Severe disease can range from dangerous lung complications to the fungus spreading into other parts of the body. Surgery is sometimes necessary when the fungus infects the spine and other parts of the nervous system. 

Blastomycosis can be fatal, especially in people with weakened immune systems or who are not diagnosed early in their infections.

According to a letter released by NIOSH following its initial visit last month, the agency urged the company to take a range of additional precautions to curb additional cases, including providing N95 respirators, inspecting its ventilation systems and limiting projects like excavations, which can stir up the soil.

On its return visits, federal investigators plan to offer urine tests to screen for missed fungal infections among employees, collect samples from around the campus, as well as administer questionnaires of workers that could help track down the original source of the fungus.

Billerud initially said Tuesday it was following the federal recommendations and was able to continue to run mill operations “uninterrupted” at the plant despite the outbreak among its employees and contractors.

That changed on Thursday, after the company announced it had decided to “temporarily idle” the plant in order to find and address the root cause of the Blastomycosis sicknesses.

“As a precautionary measure, we will temporarily idle the Escanaba Mill for up to three weeks to facilitate additional proper cleaning based on recommendations from NIOSH and other organizations, which requires larger portions of the mill to be vacant while this work is performed,” Christoph Michalski, Billerud’s president and CEO, said Thursday in a statement.