Source of fungal lung infections has spread outside historical borders

Three species of soil fungi, known to cause lung infections, have been found in U.S. states outside of what was historically accounted for by the CDC in 1969, according to a study published in Clinical Infectious Diseases.

These three main species of soil fungi are Histoplasma, Coccidioides and Blastomyces.

“We have been assuming the geographic distribution of Histoplasma, Coccidioides and Blastomyces have been evolving and getting larger,” Patrick B. Mazi, MD, infectious disease clinical fellow at Washington University School of Medicine in St. Louis, told Healio. “There are some great mathematical models predicting geographic expansion of these fungi, and there is growing epidemiological data and case series/reports of these fungi supporting the model predictions. I think our work is really more supporting evidence for this, but with more than 45 million individual patients, it is at a much larger scale.”

In a retrospective analysis, Mazi and colleagues evaluated more than 45 million Medicare recipients across all U.S. states and Washington, D.C., from Jan. 1, 2007, to Dec. 31, 2016, to determine how many cases of fungal lung infections there were for each county, prompted by an increase in recent diagnoses.

Researchers looked at Histoplasma, Coccidioides and Blastomyces individually to determine the number of lung infections for each county and state per 100,000 person-years, using 100 cases per 100,000 person-years as the clinically meaningful threshold for histoplasmosis and coccidioidomycosis and 50 cases per 100,000 person-years as the threshold for blastomycosis.

From 3,143 U.S. counties, researchers reported 79,749 diagnoses of histoplasmosis, 37,726 of coccidioidomycosis and 6,109 of blastomycosis. In terms of clinically meaningful cases, 1,806 counties met the threshold for histoplasmosis cases, along with 339 counties for coccidioidomycosis and 547 counties for blastomycosis.

Researchers found that 94% of states plus D.C., had at least one county above the threshold for histoplasmosis, with corresponding rates of 69% for coccidioidomycosis and 78% for blastomycosis. Historically, Histoplasma fungi were limited to the Midwest and parts of the East, whereas Coccidioides primarily were found in the Southwest and Blastomyces in the Midwest and South, according to a press release.

“I believe anthropogenic climate change is a major driver of the changing geographic distribution of histoplasmosis/blastomycosis/coccidioidomycosis because these dimorphic fungi maintain environmental reservoirs; they are inextricably linked with the local environment,” Mazi told Healio. “Because of this, I think they are excellent subjects to research how climate change affects epidemiological patterns of infectious disease.”

With these findings, researchers reported that diagnoses of soil fungi, or dimorphic mycoses, have spread outside of their historical borders that were last reported by the CDC in 1969 and clinicians should account for this when making a diagnosis.

“My recommendation for practicing clinicians would be to send off histoplasmosis/blastomycosis/coccidioidomycosis testing for every patient with a compatible clinical syndrome and not to place so much emphasis on travel history/exposure,” Mazi said. “Travel can still certainly raise our index of suspicion, but lack of travel should not prevent these pathogens from being included on a differential or dissuade clinicians from ordering testing.”

Mazi also told Healio that authors of this study have collaborated with Matthew Pullen, MD, from University of Minnesota, to create mycoses.org, a website that allows for easier access to data on incidence rates for these pathogens in specific practice areas of clinicians.

For more information:

Patrick B. Mazi, MD, can be reached at pmazi@wustl.edu.

Reference:

Lung infections caused by soil fungi are a problem nationwide. https://medicine.wustl.edu/news/lung-infections-caused-by-soil-fungi-are-a-problem-nationwide/. Published Nov. 16, 2022. Accessed Nov. 17, 2022.