A Rare but Deadly Fungal Infection Is Cropping Up in More States

An illustration of Blastomyces dermatitidis fungi, a common cause of blastomycosis.

An illustration of Blastomyces dermatitidis fungi, a common cause of blastomycosis.

A dangerous fungal infection has seeded its spores farther across the United States than previously assumed. Research out this week details evidence that cases of blastomycosis are regularly showing up in Vermont, outside of the established areas of the U.S. where it’s thought to be endemic.

Blastomycosis is an infection caused by a group of fungi called Blastomyces. These infections usually happen when people breathe in spores that have been kicked up into the air from the soil or surrounding environment, though only some people will become sick as a result of exposure. Symptoms are often respiratory and include fever, cough, muscle aches, and fatigue. But the infection can sometimes spread beyond the lungs and cause severe, life-threatening illness, particularly in people with weakened immune systems.

The fungi are assumed to be endemic in parts of the midwestern, south-central, and southeastern U.S., and only five states currently keep track of diagnosed human cases: Arkansas, Louisiana, Michigan, Minnesota, and Wisconsin. But there’s been some indication that the potential range of blastomycosis in the U.S. is larger than we think. Researchers at the Centers for Disease Control and Prevention and the Vermont Department of Health decided to take a closer look, analyzing insurance claims data from Vermont residents from 2011 to 2020.

Overall, they identified 114 patients with blastomycosis diagnosed in Vermont during those years, amounting to an annual incidence rate of 1.8 patients per 100,000 people. Of these cases, 30% were hospitalized as a result and four ultimately died from their infection.

Blastomycosis is a rare disease, but Vermont’s incidence rate is actually higher than the recent incidence rates seen in four out of the five states where the disease is tracked, the study authors note. In other words, the disease may be just as or even more common in Vermont than it’s thought to be in known endemic areas.

“Our findings, based on the most comprehensive assessment of blastomycosis in Vermont to date, align with a growing body of evidence suggesting that the burden of endemic blastomycosis is greater than commonly appreciated,” the authors wrote in their paper, published Wednesday in the journal Emerging Infectious Diseases.

This research alone can’t tell us whether blastomycosis has started to spread to more parts of the U.S. over time or if we’ve simply failed to notice its presence until now. But there is evidence that other fungal diseases have expanded their range in the U.S. in recent years—an expansion that has likely been aided by factors like climate change. So it’s certainly possible that the same is true for blastomycosis. In any case, the authors say more study is needed to better understand the true threat that blastomycosis poses to our public health, and that doctors should be made more aware of the disease in general.

“These results challenge routine assumptions about the epidemiology and ecology of this disease and reflect a need for future studies,” they wrote. “Clinicians should consider blastomycosis in patients with compatible signs and symptoms. Standardized surveillance could also improve our understanding of exposures, risk factors, and clinical outcomes.

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