At least 109 people in Michigan are believed to be infected with a rare fungus after five more cases were noted last week.
The outbreak has been linked to a paper mill in Escanaba, Upper Peninsula, and is one of the largest fungal clusters in U.S. history.
The cases are caused by the infection blastomycosis, a rare fungal disease caused when people inhale spores after disturbing rotten wood or leaf litter.
Thirteen of the patients have been hospitalized and one person has died. It was not clear if anyone is in critical condition.
Health officials fear further cases will be discovered in the coming weeks, as it can take months for patients to develop symptoms.
Pictured above is the Billerud paper mill in Escanaba, Michigan’s upper peninsula, where the outbreak was discovered. One person has died, 13 have been hospitalized and there are 109 cases
The outbreak has been going on at the plant since late February, when the first cases were discovered. The mill is closed for thorough cleaning
All patients are employees, contractors or visitors to the mill, local health authorities say, which closed in mid-April after authorities failed to find the source of the outbreak.
The latest update covers the week to April 28 and was released this Friday and sounded the alarm about the growing outbreak.
The Mill has consistently reported several cases each week in April, with another seven the week before and four the week before.
Investigators have yet to find a source for the outbreak, though it may be wood that arrived at the paper mill.
The ventilation system is also now being thoroughly cleaned out of concern that it could spread the infection.
Humans catch the fungus by inhaling the spores. Infected patients cannot pass the fungus on to other people.
Michael Snyder, a local health official, said in a statement that they continued to see “fewer new cases” each week.
He added: “Many of these cases have been showing signs and symptoms since March.”
The outbreak is believed to be the largest blastomycosis outbreak in U.S. history to date, with the previous largest in Wisconsin in 2010 leading to 55 infections, 30 hospitalizations and two deaths.
On average, the fungus is responsible for about 6,700 cases and 60 deaths per year in the US. Outbreaks normally number fewer than ten individuals.
Blastomycosis was first diagnosed at the plant in late February, but it took more than a month for Billerud to order the plant closed – initially telling staff to wear face masks to prevent infection.
The company said it was first warned about the blastomycosis outbreak in early March, when workers first tested positive for the fungus.
It was not clear how the outbreak came about, but the fungus is known to live in rotten wood and damp leaf litter.
Gerald Kell, who heads the United Steelworkers union representing workers at the plant, said earlier that some workers needed hospital care for weeks.
The first fatal accident was confirmed in mid-April to a contractor who had worked at the plant.
Jamie Dier, vice president of the union, told DailyMail.com that those who had become seriously ill “couldn’t breathe” and were “coughing up blood or phlegm.”
Their lungs fill with nodules [of the fungus],” he said, “there are fungal masses on their lungs that prevent them from breathing.”
Blastomycosis (stock image of fungus Blastomyces) can cause symptoms similar to a cold in the early stages, but the fungus can then spread to other parts of the body and cause more serious illness
Mr Dier said he had to battle a six-week infection with the fungus that left him short of breath and fungal nodules in his lungs, but he has since recovered.
Billerud, the Swedish company that owns the mill, closed it in mid-April as a “precautionary measure” to allow thorough cleaning.
There were also fears that more patients could become infected, while researchers were still unable to identify the potential source of the outbreak.
Mill leaders have been working with health agencies including the Centers for Disease Control and Prevention (CDC) and the local Department of Health to bring the outbreak under control.
Paper produced by the factory is used in magazines and pamphlets, workers say.
Blastomycosis starts in the lungs and causes symptoms such as cough, fever, and chest pain, but in severe cases it can spread to other areas such as the skin, bones, and the brain and spinal cord.
Medications are available to treat the condition, including antifungal drugs — such as itraconazole — which work by disrupting the wall of fungal cells, causing cell leakage and eventually death.
However, those taking these drugs may need to continue taking them for a year to clear the infection.
Blastomycosis is rare nationwide, with only about one or two cases per 100,000 people reported nationwide each year.
The disease has a death rate of about one in 100 patients, according to the Centers for Disease Control and Prevention (CDC).
The infection also does not spread from person to person, public health officials say.