ESCANABA — More information has been released about a fungal outbreak linked to Billerud’s Escanaba paper mill in 2022 and 2023 that infected at least 162 people and resulted in one death.

The outbreak of blastomycosis — a fungal disease caused by the inhalation of Blastomyces spores that can result in a potentially fatal form of pneumonia — was the largest outbreak of the disease on record in the United States and the only outbreak associated with a paper mill or other industrial worksite. Typically, the disease is caused when soil where the fungus lives is disturbed, and prior to the Escanaba outbreak, work-place related outbreaks were limited to industries like farming, construction and landscaping, according to an article published in the most recent issue of the Centers for Disease Control and Prevention’s “Morbidity and Mortality Weekly Report.”

In early March 2023, Public Health Delta and Menominee Counties reported a cluster of blastomycosis cases among mill workers to the Michigan Department of Health and Human Services, which in turn contacted the CDC. Mill management contacted a health hazard evaluation from the CDC’s National Institute for Occupational Safety and Health (NIOSH) on March 17 to identify any potential sources of the outbreak.

During the assessment, 533 indoor and outdoor environmental samples were analyzed by the Marshfield Clinic Research Institute and the Wisconsin State Laboratory of Hygiene, but no Blastomycyes was detected. However, the CDC noted that because of challenges in identifying Blastomyces in the environment, the lack of positive samples does not rule out the presence of the fungus at the mill.

“This was not an unexpected outcome as Blastomyces is an elusive organism,” said Jennifer Meece, executive director of the Marshfield Clinic Research Institute who has researched blastomycosis for more than 20 years. “It is rare, if not unheard of, that the exact source of a blastomycosis outbreak has ever been detected in the environment.”

Despite the lack of positive samples, the CDC does have some ideas as to how the fungus infected both individuals who worked inside and outside at the mill. In the “Morbidity and Mortality” report, it is noted that 59 of the 67 ventilation units assessed provided unfiltered outdoor air into the mill and that many had dirt and organic debris present in the coils. The fungus does not propagate indoors, but spores may have infiltrated the buildings through unfiltered ventilation systems or bay doors, leading to indoor fungal exposure, likely over several months.

Given that there is a two-week to three-month incubation period for blastomycosis, exposure likely began as early as mid-October 2022 and extended through at least February of 2023, and possibly as late as April of 2023.

On April 13, 2023, Billerud announced it was temporarily idling the mill for three weeks. During that time, ductwork was cleaned and filters were upgraded in all air handling units. Training was also provided for workers about blastomycosis during that period.

While the search was on to find the source of the outbreak, information was being gathered about those infected. NIOSH conducted a medical survey that included a work and health questionnaire and urine analysis for Blastomyces antigen testing, which identified potential cases that were asymptomatic or had otherwise not been detected. According the CDC, all paper mill employees, contractors and visitors to the mill were invited to participate in the survey, though only 603 participated of the roughly 1,000 mill workers. Information was added to the study from an additional 42 mill workers who were diagnosed with the disease but did not participate in the survey, for a total of 645 participants.

The data revealed a number of trends in who developed the disease. Workers with blastomycosis tended to be younger, with a shorter tenure at the mill than workers who did not contract the disease. Based on workers’ primary work locations, the mill areas with the highest blastomycosis case counts were paper machine line #1 (35 cases) and maintenance (22 cases), though workers from all areas of the mill were affected, including the administrative offices (17 cases).

The assessment of the 645 participants identified blastomycosis in 162, with the onset of symptoms taking place between Nov. 1, 2023 and May 15, 2024, and the weekly case county peaking at 21 cases in early March of 2023, prior to the mill’s temporary idling. Of those 162, 120 were identified among the 603 NIOSH medical survey participants, suggesting an estimated 20% of mill workers were infected with the disease.

One half of the workers who tested positive based on the NIOSH urine test for antigens did not report a blastomycosis diagnosis, suggesting the survey identified cases that were not included in MDHHS’ surveillance data.

According to the CDC, 12% of workers with blastomycosis were hospitalized during the outbreak and 63% showed abnormal lung findings on chest imaging.

The one death associated with the outbreak was reported by PHDMC as being a contractor who worked at the mill. The Daily Press has independently confirmed at least one other infection linked to the outbreak was also a contractor, however data from the CDC does not differentiate between mill employees and contracted workers, likely for privacy reasons.

No new cases were identified among those who had worked at or visited the mill after the mill’s idling, and only one case was identified in Delta County during the outbreak that had no association to the mill.