Soil-borne fungi whose spores can cause severe lung infections may be far more widespread in the U.S. than experts thought, a new study suggests.
These fungi include Histoplasma, known as histo for short, which is a genus of fungus that causes histoplasmosis. Authoritative sources, such as the Centers for Disease Control and Prevention (opens in new tab) (CDC) and the online medical resource StatPearls (opens in new tab), state that the fungi can be found in central and eastern U.S. states, particularly in areas near the Ohio and Mississippi River valleys.
However, according to the new research, Histoplasma can likely be found in 47 U.S. states, plus Washington, D.C., and is growing at clinically significant levels in at least one county per affected state.
"Every few weeks I get a call from a doctor in the Boston area — a different doctor every time — about a case they can't solve," senior study author Dr. Andrej Spec (opens in new tab), an associate professor of medicine and a specialist in fungal infections at the Washington University School of Medicine in St. Louis, said in a statement (opens in new tab). "They always start by saying, 'We don't have histo here, but it really kind of looks like histo.' I say, 'You guys call me all the time about this. You do have histo.'"
The new study, published Nov. 11 in the journal Clinical Infectious Diseases (opens in new tab), analyzed Medicare fee-for-service claims made between 2007 and 2016 to determine the rate of fungal infection diagnoses in the 50 states and D.C. The team included data only from Medicare beneficiaries ages 65 and older, so it's not a complete picture of all the fungal infections in each state, the study authors noted.
In addition to histo, the team specifically looked for cases of blastomycosis, an infection caused by fungi in the genus Blastomyces, and valley fever or coccidioidomycosis, which is caused by fungi in the genus Coccidioides. Historically, Blastomyces has been found in Midwestern, South Central and Southeastern states, and around the Ohio and Mississippi River valleys, the Great Lakes and the St. Lawrence River, according to the CDC (opens in new tab). Coccidioides has been detected in the southwestern U.S. and south central Washington, the agency says (opens in new tab).
When soil is disturbed, fungi in these genera release microscopic spores into the air. Most people don't get sick from inhaling the spores. However, some develop symptoms — such as fever, cough and night sweats — that resolve without medical treatment, and some develop severe lung infections that can then spread to other body parts, according to the CDC.
People with weakened immune systems face a high risk of severe infection from all three genera. In the case of histo, infants and adults older than 55 years old also have a high risk of serious disease, and for Valley Fever, the same is true for people who are pregnant or have diabetes.
Considering the 50 states and D.C., more than 90% of jurisdictions had histo, while 69% and 78% had at least one county with significant rates of coccidioidomycosis and blastomycosis, respectively, the team found.
To determine where the diagnoses took place, the team took beneficiaries' home addresses into account and assumed that they'd picked up the infections in their counties of residence. This is a limitation of the study, as it doesn't account for travel-related exposures, the authors noted. This is especially relevant because, depending on the infection, a person's symptoms may emerge weeks to months after they breathe in fungal spores, giving them plenty of time to hop state lines.
But regardless of its limitations, the study hints that these fungi lurk in far more states than experts once thought, and doctors should recognize the potential for these illnesses to crop up all across the country, the study authors concluded.