The fungus Histoplasma, which causes lung infections, was concentrated in the Midwest in the 1950s and 60s (top map), but now causes significant disease throughout much of the country (bottom). Researchers at Washington University School of Medicine in St. Louis discovered that the three main kinds of soil fungi that cause lung infections have all expanded their ranges in recent decades. Reliance on outdated maps could be causing delayed or missed diagnoses. Credit: Andrej Spec and Patrick Mazi.
Every few weeks, Andrej Spec, MD, assistant professor of medicine at Washington University School of Medicine gets a call from a doctor in the Boston area about a case they can’t solve. Although it’s a different doctor every time, they almost always say the same thing: “this looks like a lung infection due to soil fungi, but we don’t have that here.”
“’You guys call me all the time about this. You do have it,’” is Spec’s typical response. Although, Spec can’t really blame the other doctors as they are relying on outdated maps of disease-causing fungi last updated by the CDC in 1969. In fact, most areas are long thought to be free of deadly environmental fungi.
But the more calls Spec received, the more he and colleagues realized that was no longer true. Now, their new study shows soil fungi cause a significant number of serious lung infections in 48 out of 50 states and the District of Columbia.
There are three main species of soil fungi in the U.S. that cause lung infections. Historically, Histoplasma was found in the Midwest and parts of the East, Coccidioides in the Southwest, and Blastomyces in the Midwest and the South. But a growing number of case reports suggest all three have expanded out of their traditional ranges in recent decades—most likely due to climate change.
While most healthy adults and children can fight off a fungal infection fairly easily, infants, older adults and those with compromised immune systems can develop fever, cough, fatigue and other symptoms. Fungal lung infections can also easily be mistaken for bacterial or viral lung infections, such as COVID-19, bacterial pneumonia and tuberculosis.
“People with fungal lung infection often spend weeks trying to get the right diagnosis and appropriate treatment, and the whole time they’re feeling terrible,” said lead author Patrick Mazi, MD, a clinical fellow in infectious diseases. “They usually have multiple health-care visits with multiple opportunities for testing and diagnosis, but the doctor just doesn’t consider a fungal infection until they’ve exhausted all other possibilities.”
For the study, published in Clinical Infectious Diseases, Spec, Mazi and team calculated the number of fungal lung infections nationwide from 2007 to 2016 using Medicare fee-for-service claims from all 50 states and the District of Columbia. Using the patients’ home addresses to identify counties of residence, they calculated the number of cases per 100,000 person-years for each county. (Person-years are a way to correct for the fact that counties can have different population sizes; one person on Medicare for one year is one person-year).
In their analysis, the researchers defined counties with more than 100 cases of lung infection caused by Histoplasma or Coccidioides or 50 cases caused by Blastomyces per 100,000 person-years as a “meaningful” number.
Of the 3,143 counties in the U.S., the team discovered 86% had a meaningful number of fungal lung infections. Of that 86%, more than half of the counties had lung infections caused by Histoplasma, 339 counties had infections caused by Coccidioides, and 547 caused by Blastomyces.
The counties were distributed across the majority of the U.S. According to the study, 94% of U.S. states had at least one county that had a Histoplasma lung infection problem, while 69% had a Coccidioides issue and 78% had a Blastomyces fungal problem.
“Fungal infections are much more common than people realize, and they’re spreading,” said Spec. “The scientific community has underinvested in studying and developing treatments for fungal infections. I think that’s beginning to change, but slowly. It’s important for the medical community to realize these fungi are essentially everywhere these days and that we need to take them seriously and include them in considering diagnoses.”