Research indicates that the fungus blastomycosis may be more common than previously believed

A report published in Emerging Infectious Diseases yesterday suggests that a fungal disease that is rare but potentially fatal could be widespread in a larger area than previously believed.

The environmental fungus Blastomyces, which is present in damp soil and decomposing organic materials, is the cause of the disease blastomycosis. The fungus can induce pneumonia-like symptoms and result in severe sickness, with death rates as high as 22%, while the majority of individuals who breathe in spores don’t get sick.

Blastomycosis has historically been thought to be endemic in states along the Ohio and Mississippi rivers, the Great Lakes, and the St. Lawrence Seaway, based on infrequent case reports and documented outbreaks. Annual incidence rates in those areas are estimated to range from 0.2 to 2.0 cases per 100,000 people. Only the states of Arkansas, Louisiana, Minnesota, Michigan, and Wisconsin conduct public health surveillance.

Increased prevalence in Vermont

However, researchers with the Centers for Disease Control and Prevention and the Vermont Department of Health looked at data from the state’s all-payer health insurance claims to identify diagnoses of blastomycosis, based on recent evidence suggesting that incidence in the Northeast may be greater than known. Between 2011 and 2020, 114 individuals (median age 55, 59% male) were diagnosed with blastomycosis.

The average yearly statewide incidence of 1.8 cases/100,00 individuals is higher than the average yearly occurrences in four of the five states that required reporting between 1987 and 2017 and higher than the incidences recorded in other states situated in known endemic areas, namely Missouri, Mississippi, and Illinois.

“Although differences in surveillance methods and case definitions among states make direct comparisons difficult, Vermont’s burden of blastomycosis appears comparable to, and perhaps higher than, most states that have published blastomycosis incidences,” the researchers said.

Of the 114 individuals that were diagnosed, 30 required hospitalization for blastomycosis at least once, and 4 passed away as a result of the infection. Three counties in the state’s north-central region—Lamoille, Orleans, and Washington counties—accounted for about half of the case-patients and 65% of hospitalized patients.

More surveillance is required

The authors point out that Vermont has a lot of acidic spodosol soil, which is thought to encourage Blastomyces growth, much like hyperendemic areas of Wisconsin. Expanded surveillance is required, they suggest, and doctors should evaluate blastomycosis in patients with comparable signs and symptoms.

“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,” they said. “These results challenge routine assumptions about the epidemiology and ecology of this disease and reflect a need for future studies.”

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