Testing began last March when 15 employees at the paper mill experienced pneumonia-like symptoms.
Health officials started the investigation after employees got sick early this year. They were initially though to have "atypical" pneumonia before testing results showed that they had a rare fungal infection called blastomycosis.
The public health department reported that as of April 14, Friday, at least 19 cases have been confirmed at the paper mill, with 74 more probable cases being monitored. (Related: Oregon hospital reports outbreak of rare fungal superbug.)
Billerud is a multinational paper and packaging company based in Sweden.
Blastomycosis is caused by the fungus Blastomyces, which can usually be found in moist soil and decomposing organic matter, like wood.
According to the Centers for Disease Control and Prevention (CDC), blastomycosis spreads through the inhalation of fungal spores.
Symptoms of blastomycosis usually appear between three weeks and three months after you inhale the fungal spores.
Health experts warn that those with weakened immune systems may develop severe blastomycosis. In some cases, the infection can spread to the lungs and other parts of the body, such as the skin, bones, joints and the central nervous system (brain and spinal cord).
Brian Peterson, Billerud's vice president of operations, expressed his thanks to the local, state and federal health agencies for assisting in the investigation at the mill.
"Although the source of the infection has not been established, we continue to take this matter very seriously and are following recommendations from health and government officials and implementing numerous, proactive steps to protect the health and safety of our employees, contractors and visitors," said Peterson in a statement.
On April 11, the company announced that it has implemented recommendations from experts since the outbreak. The enforced measures include retaining an industrial hygienist, testing raw materials, providing workers with N95 masks and conducting deep cleanings at the mill.
In a statement, Billerud said it can be difficult to identify the source of the fungal outbreak because the Blastomyces fungus is endemic to the area. There has also "never been an industrial outbreak of this nature documented anywhere in the U.S." that can provide experts with helpful data to address the issue.
Billerud's Michigan mill was founded in 1911 as the Escanaba Pulp and Paper Co. on the bank of the Escanaba River.
According to the CDC, Blastomyces, the fungus that spreads the infection, is commonly found in the areas surrounding the Great Lakes, as well as the Ohio, Mississippi and Saint Lawrence Rivers. Billerud's website reports that there are more than 800 workers currently employed at the mill, which produces about 730,000 tons of paper annually.
Watch the video below as the CDC warns of dangerous fungal infections spreading across America at an alarming rate.
This video is from the GalacticStorm channel on Brighteon.com.