By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: The largest reported outbreak of blastomycosis has affected at least 115 employees, contractors, or visitors to a paper mill in the Michigan Upper Peninsula.
SOURCES: Public Health Delta & Menominee Counties. Blastomycosis Investigation. https://phdm.org
Centers for Disease Control and Prevention. The National Institute for Occupational Safety and Health (NIOSH). NIOSH investigates workplace outbreak of blastomycosis. Last reviewed April 19, 2023. https://www.cdc.gov/niosh/newsroom/alerts/blastomycosishhe.html
On March 3, 2023, the Delta & Menominee Counties Public Health Department (PHD) in Escanaba, MI, notified the Escanaba Billerud paper mill that several employees had developed severe atypical pneumonia. Subsequently, it was determined that the employees had pulmonary blastomycosis and, with increasing case numbers, mill operations were interrupted.
The PHD reported on May 6, 2023, that a total of 115 cases of blastomycosis had been identified and that 14 patients (12.2%) had required hospitalization and one had died. All cases were in employees, contractors, or visitors with the same paper mill.
After inspection, the National Institute for Occupational Safety and Health (NIOSH) recommended making N95 respirators available to all workers for voluntary use; inspecting and maintaining heating, ventilation, and air conditioning systems; and inspecting ductwork for water incursion or microbial growth. It was recommended that activities involving soil disruption be limited. Finally, they recommended continued encouragement of symptomatic employees to visit their healthcare providers. They subsequently collected soil, dust, wood chips, and ventilation system filter material for testing for the presence of Blastomyces. After a “deep cleaning,” work resumed at the mill on May 8, 2023. It was also reported at that time that Blastomyces had not been identified in environmental samples.
A number of outbreaks of blastomycosis have been reported previously, often in individuals recreating along waterways or areas with ongoing soil excavation. A small cluster, first recognized in dogs, was reported recently from Wisconsin.1 A total of four humans and five dogs were affected. The largest outbreak, until the one reviewed here, involved 55 individuals in Marathon County, WI, in 2009-2010. Of the 55, 70% were hospitalized and 5% died.2 There was no common source, and household and neighborhood clustering suggested multiple environmental sources. Of note is that 45% were of Hmong ancestry.
These events occurred, as expected, in endemic areas. However, it should be recognized that cases of all the endemic mycoses may be acquired outside these areas and that endemicity may be expanding, perhaps in part as a consequence of climate change.3,4
- Roy M, Benedict K, Deak E, et al. A large community outbreak of blastomycosis in Wisconsin with geographic and ethnic clustering. Clin Infect Dis 2013;57:655-662.
- Segaloff HE, Wu K, Shaw S, et al. Notes from the Field: Cluster of blastomycosis among neighborhood residents — St. Croix County, Wisconsin, 2022. MMWR Morb Mortal Wkly Rep 2023;72:348-349.
- Benedict K, Thompson GR 3rd, Deresinski S, Chiller T. Mycotic infections acquired outside areas of known endemicity, United States. Emerg Infect Dis 2015;21:1935-1941.
- Mazi PB, Sahrmann JM, Olsen MA, et al. The geographic distribution of dimorphic mycoses in the United States for the modern era. Clin Infect Dis 2023;76:1295-1301.