In 2022–2023, the largest known outbreak of blastomycosis in the United States occurred at a paper mill in Michigan. However, no source was identified by environmental sampling of the mill as the source of Blastomyces exposure, and this was the first outbreak of blastomycosis in an industrial, primarily indoor setting.
A fungal infection known as blastomycosis is usually spread by inhaling Blastomyces spores, which spread environmentally with severe pulmonary disease leading to frequent hospital visits. The update was based on the weekly news posted by the Centers for Disease Control and Prevention (CDC) on January 2nd.
At the beginning of March 2023 Public Health Delta and Menominee Counties, MI, observed blastomycosis cases specifically among people working in paper mills, and reported them to the MI Department of Health and Human Services (MDHHS). The agency later notified the CDC that MDHHS. On March 17th, paper mill management requested a health hazard evaluation (HHE) from the CDC’s National Institute for Occupational Safety and Health (NIOSH) to investigate the possible spread of Blastomyces in the workplace and provide recommendations for preventing and controlling the illness at the paper mill.
A total of 645 paper mill workers, of whom 162 had illness onset from November 1, 2022–May 15, 2023, along with the increased case count per week by 21 in early March 2023, were assessed for blastomycosis. Environmental sampling including HHE samples did not determine the origin of Blastomyces exposure in the mill workers. This was the largest reported blastomycosis outbreak in the U.S., and the first ever documented in an industrial setting or paper mill. Swift prohibition calculations were based jointly on mill cleaning, hazard communication, respiratory protection, and ventilation system improvements, which coordinated public health response and aided the implementation of the recommendations.
On March 6, Public Health Delta and Menominee Counties (PHDM) notified area healthcare providers to be aware of potential additional cases. Within seven days, MDHHS informed the CDC’s Mycotic Diseases Branch (MDB), National Institute for Occupational Safety and Health (NIOSH), and CDC about the eight blastomycosis cases, including an additional uncertain 14 cases to be diagnosed, among the workers at or visited the paper mill (workers) before the blastomycosis outbreak onset. On Saturday, February 28, 2023, PHDM in Michigan was notified by mill workers and management of a cluster of atypical pneumonia cases among workers at a local paper mill in Delta County, Michigan; respiratory symptoms onset occurred in all patients occurred between January and February 2023, and the specimen was shown to be positive for Blastomyces urine antigen.
Around 1,000 workers, 603 were part of the medical survey. A total of 42 mill workers with blastomycosis, but who were not participating in the NIOSH HHE and whose identification and contact information NIOSH had, were involved in this investigation which was coordinated via a data use agreement between NIOSH and MDHHS and with voluntary workers consenting to use information about HHE with public health authorities; these individuals contributed a total of 645. From October 1, 2022–July 1, 2023, a person who worked at or visited the mill during that period was considered an outbreak case if the person had 1 or more of the following: confirmed or speculative laboratory evidence of blastomycosis or health care provider diagnosed blastomycosis. The NIOSH medical survey involved all paper mill employees, contractors, and visitors.
From April 17th to May 7th, 2023, paper mill management voluntarily idled production for air ductwork cleaning and filter improvements of all air handling units. NIOSH, MDB, PHDM, and MDHHS staff conducted 10 sessions from April 20–21 for workers to receive information regarding blastomycosis and the NIOSH HHE.
During the outbreak, NIOSH advised that wear a fit-tested, NIOSH-approved N95 respirator, particularly, those workers who are at risk for severe disease (e.g., immunosuppressed), or those performing potentially high-risk tasks (e.g., HVAC filter change or soil disturbance). Routine conference calls and interim letters were used to communicate HHE findings and recommendations to paper mill managers, workers, and public health partners.
83% of workers were male (98% Caucasian, 96% non-Hispanic, 46 median [between 19–73 years]). In the epidemiologic investigation of the 645 workers who were included, 162 of the workers were diagnosed with blastomycosis and routinely reported signs and symptoms of cough (90%), shortness of breath (76%), fatigue (76%), fever or chills (73%); and abnormal lung findings on chest image (63% of patients). Cough was reported by 61% (294) of the 483 workers who were unaffected by blastomycosis. Eighteen (12%) workers were hospitalized due to blastomycosis, and one patient died. Of 573 NIOSH medical survey workers with Blastomyces urine antigen results, 52 (9%) tested positive, 26 (50%) had not reported a prior diagnosis of blastomycosis before the survey, and 3 workers (6%) reported no signs or symptoms.
One Delta County blastomycosis case without a link to the mill occurred from October 1, 2022, through July 1, 2023. No further cases among mill workers were identified by April 2024.
Reference: Harvey RR, O’Connor AW, Stanton ML, et al. Outbreak of Blastomycosis Among Paper Mill Workers — Michigan, November 2022–May 2023. MMWR Morbidity and Mortality Weekly Report. 2024;73(5152):1157-1162. doi:https://doi.org/10.15585/mmwr.mm735152a2
