The First CDC Morbidity and Mortality Weekly Report (MMWR) of 2025
The largest blastomycosis outbreak linked to a paper mill in Michigan and a 56% increase in tularemia cases over the past decade.
CDC logo
Image credits: CDC
This year's first CDC Morbidity and Mortality Weekly Report (MMWR) highlights two public health concerns in the United States: the largest recorded outbreak of blastomycosis linked to a paper mill in Michigan and a 56% increase in tularemia cases from 2011 to 2022. These findings underscore the need for enhanced prevention measures and better disease monitoring in affected populations.
Largest US Blastomycosis Outbreak Linked to Paper Mill in Michigan1
In late 2022, a large outbreak of blastomycosis, a fungal infection that can cause severe pulmonary illness, was identified among workers at a paper mill in Delta and Menominee Counties, Michigan. The outbreak led to 162 confirmed cases, marking the largest blastomycosis outbreak ever recorded in the US.
Blastomycosis is contracted by inhaling fungal spores typically found in soil, wood, or leaves. In early March 2023, the Michigan Department of Health and Human Services (MDHHS) alerted the CDC after a cluster of cases was reported among mill workers. The National Institute for Occupational Safety and Health (NIOSH) was involved to assess potential workplace exposures.
From November 2022 to May 2023, the investigation documented 162 cases, with the highest number of cases reported in early March 2023, when 21 workers fell ill in one week. Despite environmental sampling, investigators could not identify a specific source of exposure within the mill. This outbreak, the first linked to an industrial setting, prompted preventive measures by health agencies.
“Paper mill managers acted quickly after outbreak recognition to engage public health authorities and implement prevention measures. Rapid and coordinated public health actions by local, state, and federal public health authorities and information sharing among partners enabled a swift response to protect mill workers,” investigators said.
The investigation faced challenges in identifying Blastomyces from environmental samples and in timing the NIOSH HHE medical survey, given the variable incubation period for blastomycosis. Additionally, many workers who self-reported blastomycosis had already been prescribed antifungal treatment, potentially affecting urine antigen test results. Despite these challenges, paper mill managers quickly engaged public health authorities and implemented prevention measures. Coordinated actions at the local, state, and federal levels facilitated a rapid response to protect mill workers.
Despite challenges in identifying Blastomyces in environmental samples and complications from antifungal treatment affecting test results, public health agencies quickly implemented prevention measures. This outbreak highlights the need for ongoing surveillance in industries where fungal spores are a risk.
Increase in Tularemia Cases in the US From 2011 to 20222
Tularemia, a bacterial disease caused by Francisella tularensis, increased by 56% in the US from 2011 to 2022, with 2,462 confirmed cases reported across 47 states. The highest incidence occurred in children, older men, and American Indian or Alaska Native populations, with rates in these groups higher than in White individuals.
Tularemia is spread through insect bites, direct contact with infected animals, or inhalation of contaminated dust. The case fatality rate is low (<2%) but increases if diagnosis or treatment is delayed. The increase in tularemia cases may reflect either a true rise in infections or better reporting and diagnostic practices, such as PCR-based detection.
From 2011 to 2022, the annual incidence of tularemia increased from 0.041 to 0.064 cases per 100,000 population. Incidence was high in children aged 5-9 years (0.083 per 100,000) and adults aged 65-84 years (0.133–0.161 per 100,000). Four central states—Arkansas, Kansas, Missouri, and Oklahoma—accounted for nearly half of the cases.
Four central states, Arkansas, Kansas, Missouri, and Oklahoma—accounted for half of all cases, reflecting regional variation in disease prevalence. “AI/AN persons remain the demographic group most affected by tularemia, with incidence in this group approximately five times that among White persons,” according to the investigators.
This report has three main limitations. First, the CDC receives limited clinical and laboratory details for most cases, as these are reported voluntarily by state health departments. Second, differences in surveillance practices across states and over time may affect the completeness of the data. Lastly, the COVID-19 pandemic may have impacted health departments' ability to classify possible tularemia cases.
The blastomycosis outbreak in Michigan and the rise in tularemia cases show ongoing public health challenges. These findings emphasize the need for coordinated responses, preventive measures, and surveillance to protect vulnerable populations. Public health actions, awareness, and provider education are essential in addressing these infections.
