May 23, 2024

NIOSH Investigates Unusual Outbreak of Fungal Disease at Paper Mill

By Kay Bechtold

On Tuesday at an AIHA Connect pop-up session, NIOSH's Ryan LeBouf, PhD, CIH, shared details about an ongoing health hazard evaluation involving a blastomycosis outbreak among paper mill workers in northern Michigan. The disease is associated with the fungus Blastomyces, which grows in moist soil and decomposing matter, such as wood and leaves. People can get blastomycosis by breathing fungal spores in the air. This rare fungal infection is "tricky" because it can take three weeks to three months after exposure for a person to develop symptoms, LeBouf said. The outbreak of blastomycosis was first identified after healthcare providers reported 15 cases of blastomycosis to the local health department by Feb. 28, 2023. By mid-March, the number of cases had climbed to 35 and the mill submitted its request for a NIOSH hazard evaluation, LeBouf said. The mill voluntarily idled in mid-April, as recommended by NIOSH, to allow the facility to be cleaned.

The mill sits on about 2,000 acres and produces around 700,000 tons of graphic paper per year, LeBouf explained. Production runs 24 hours a day in multiple connected buildings, and the facility employs more than 800 workers, plus some contractors. NIOSH's evaluation included a medical survey, which involved an interviewer-administered research electronic data capture, or REDCap, survey on worker health of more than 600 people, as well as urine antigen testing for nearly 580. NIOSH found the case prevalence to be 16 to 20 percent, with 160 workers meeting the agency's case definition for blastomycosis.

NIOSH also conducted an environmental survey in which agency personnel assessed the mill's heating, ventilation, and air conditioning (HVAC) system and collected more than 500 samples, including surface dust from office buildings, production areas, and HVAC components. NIOSH also collected samples from used HVAC filters and duct liners and of soil, bulk dust, and raw material. No Blastomyces was detected by polymerase chain reaction or culture, LeBouf said, adding that this finding is not abnormal because the fungus is difficult to find and analyze. NIOSH's assessment of the mill's ventilation equipment identified some problematic areas: for example, agency staff found dirty coils in makeup air units and noted that some of the units didn't have filters. LeBouf also said that the recirculating air handling units NIOSH assessed had only MERV 8 or 9 filters installed.

The NIOSH team is currently analyzing the data from its evaluation. LeBouf said the agency collected extensive epidemiological data and information about workers' primary and secondary work locations, but so far, they have not been able to identify a source. In response to a question from the AIHA Connect audience, LeBouf stated that the blastomycosis cases did not seem to be clustered in a particular category of employees. When asked if he had any guesses as to a source, LeBouf explained that since Blastomyces is typically found in moist soils, the source is likely somewhere outside the plant. He mentioned that the water level in the river near the mill was historically low, so the soil along the river was one possibility. However, LeBouf stressed that blastomycosis is usually related to community exposures. Cases are typically seen among people who've been in the woods or hiking, or among workers on construction sites where soil is being disturbed by activities like excavation. An outbreak in an occupational setting like the mill is "unheard of," he said.

Since NIOSH personnel were not sure of the source, their recommendations to protect the mill workers from exposure to Blastomyces spores in the air included properly maintaining the ventilation system and wearing personal protective equipment. NIOSH recommended that the employer install and upgrade HVAC filters in the mill, perform routine maintenance of the HVAC system, and educate workers about blastomycosis. The agency also recommended the use of fit-tested N95 respirators.

By the time the outbreak ended in May 2023, there had been more than 160 cases of blastomycosis and one fatality. An additional case recently appeared, which NIOSH is investigating now. "We're not sure if that's the normal background for the region or work-related," LeBouf said.

The final report is forthcoming. More information about NIOSH's Health Hazard Evaluation Program can be found on the agency's website.

Kay Bechtold is managing editor of The Synergist.

Read more coverage of AIHA Connect 2024.

For Further Reading

The Synergist: "Blastomycosis in Vermont" (April 2024).

The Synergist: "Blastomycosis Outbreak in Michigan" (June/July 2023).