Dimorphic fungal infections spread beyond historic geographic areas
Key takeaways:
- Histoplasmosis, coccidioidomycosis and blastomycosis are dimorphic fungal infections.
- Based on insurance claims, researchers determined that the infections have expanded beyond their typical areas of endemicity.
Maps of histoplasmosis, blastomycosis and coccidiomycosis may underestimate the areas of endemicity for these infections because researchers have found diagnoses outside their historically defined regions in the United States.
“The original maps defining areas of endemicity within the U.S. for histoplasmosis, coccidioidomycosis, and blastomycosis were based on limited skin prick testing from the 1950s and outbreak data,” Reid Goodman, MD, chief fellow in the division of infectious diseases at Washington University in St. Louis, told Healio.
“In 2023, Mazi [and colleagues] published updated maps based on International Classification of Diseases coding in a Medicare cohort. This brought about significant debate about the generalizability of their findings since it was based on a [65 years and older] cohort who may have unique travel habits and mapped cases to an infected person’s home county, not necessarily where the mold infection diagnosis was made,” Goodman said.
To determine if these findings could be generalized, Goodman and colleagues conducted a retrospective analysis of more than 21 million commercially insured individuals within the U.S. annually between 2007 and 2016. According to the study, the researchers identified histoplasmosis, coccidioidomycosis and blastomycosis cases using data within the MerativeTM MarketScan database and mapped them to the location that the diagnosis was first coded.
Throughout the study period, there were 37,513 histoplasmosis, 14,987 coccidioidomycosis and 2,207 blastomycosis — referred to collectively as dimorphic mycoses — diagnoses within 387 metropolitan statistical areas. According to the study, the dimorphic mycoses were “consistently diagnosed outside their historical hyperendemic regions.”
Specifically, the data demonstrated that histoplasmosis — which has been shown to be more common in rural areas — had the widest distribution with expansion toward the north approaching the Great Lakes, toward the south along the Gulf Coast and along the eastern U.S. coastline.
Coccidioidomycosis remained “hyperendemic” to the southwest region. However, it expanded north along the west coast, as well as further along the southern Texas border and north through the Rocky Mountains and Northern Plains toward the Canadian border.
The authors wrote that there was “minimal historical or contemporary data predicting the geographic distribution of blastomycosis,” although the data from this study suggest that diagnoses expanded outside hyperendemic regions.
Based on these findings, the authors wrote that the data show support for the initial 2023 study by Mazi and colleagues.
Goodman explained that half of patients with dimorphic fungal infections experience significant diagnostic delays, leading these patients to have delayed diagnoses and worse outcomes.
“One barrier to efficient diagnosis is the term ‘endemic’ mycoses, which creates confusion in light of evidence showing expanding geographic distributions of these infections,” he said. “We are probably underrecognizing cases of dimorphic mycoses infection by restricting testing to patients with clear exposure history to a classically hyperendemic zone. Testing for these infections should be guided by the presence of a compatible clinical syndrome, regardless of known geographic exposure.”
References:
- Goodman R, et al. Open Forum Infect Dis. 2024;doi:10.1093/ofid/ofae755.
- Mazi PB, et al. Clin Infect Dis. 2023;doi:10.1093/cid/ciac882.
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Goodman R, et al. Open Forum Infect Dis. 2024;doi:10.1093/ofid/ofae755.
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