In an update on the situation, Public Health Delta & Menominee Counties (PHDM) said that a contractor who worked at the Michigan-based mill had recently died due to blastomycosis.

Blastomycosis is caused by the Blastomyces fungus. It grows in moist soil and leaves and is endemic in Southern, Southeastern and Midwestern states of the USA and Canada.

Michael Snyder, health officer at PHDM, said: “We were saddened to hear this news. Our heartfelt sympathies and prayers go out to the family, friends and co-workers who have lost their loved one.” 

Brian Peterson, Billerud operations vice president for Escanaba Mill, commented: “Anyone who works at our facility is part of our team, and we are keeping this individual, their family, co-workers and friends in our thoughts and close to our hearts.”

There have been 21 confirmed cases of blastomycosis so far, and a further 76 people have been classified as probable cases. Twelve out of the 97 total cases have been hospitalised.

The 700,000tpa mill has been idled since 13 April to allow for additional deep cleaning and is expected to be out of action for up to three weeks. 

Escanaba Mill has 830 staff and is the largest employer in the local area. 

People can get blastomycosis infection by breathing in fungal spores from the air. It does not spread from person to person or between animals and people.

The mill first became aware of the issue in early March. 

Most people with blastomycosis will need treatment with prescription antifungal medication. 

PHDM said that, depending on the severity of the infection and the person’s immune status, the course of treatment can range from six months to one year.

Shares in Sweden-headquartered pulp and paper group Billerud have fallen to a 52-week low of SEK100.70 (£7.84) over the past month, and were at SEK102.00 at the time of writing (52-week high: SEK165.00).