Researchers at Imperial College London have confirmed that drug-resistant mold infections originating from gardens, homes, and farms are causing persistent, life-threatening illness in humans.

Molds like Aspergillus fumigatus are ubiquitous around the world, so the average person’s immune system is skilled at recognizing and clearing inhaled mold spores.

Drug resistant mold strains are on the rise worldwide, and the Imperial study, published Monday in the journal Nature Epidemiology, identifies a likely driving factor: exposure to agricultural fungicides.

While a hefty dose of fungicide will kill a mold like Aspergillus, gradual exposure in the environment can lead the way to drug resistance, Johanna Rhodes, a genomic epidemiology fellow at Imperial, told Insider.

“It’s kind of like building up a tan gradually,” Rhodes, the study’s lead author, said. “If it’s exposed a little bit at a time, it will develop the resistance slowly.”

The study is one of the first to confirm that people can catch drug-resistant fungal infections from their everyday environments.

To interrogate the connection, Rhodes and her team collected and analyzed more than 100 Aspergillus samples from infected patients across England, Wales, Scotland, and Ireland between 2005 and 2017. They also sequenced mold samples from those patients’ environments and compared them for matches.

For some patients, samples of Aspergillus taken from the lungs were nearly identical to spores found in nearby soil or other environmental sources, picked based on hospital location. In six separate cases, drug-resistant aspergillosis infections could be traced back to the patient’s environment with high confidence.

Fungi are evolving drug resistance

Researchers like Rhodes are especially interested in tracking drug-resistant mold strains, which are on the rise worldwide.

Infections with normal Aspergillus sicken 10-20 million people around the world, according to estimates cited in the study. The infection is typically treated with a class of antifungal drugs called azoles, but emerging drug resistance is a growing threat.

Almost half of the samples collected in the UK-based study were resistant to at least one first-line antifungal drug, and more than 10% of samples (including three from patients) had evolved resistance to two or more azole drugs.

Although drug resistance can emerge during treatment in hospital settings, the authors concluded that the fungi in question developed resistance before it infiltrated any human lungs, and that pointed them to agricultural fungicides.

Antifungal resistance can be deadly for patients with compromised immune systems, whether they’re on immunosuppressant medications or managing an autoimmune condition. Studies have found a 25% increase in mortality three months into infection with drug-resistant Aspergillus compared to those with typical, treatable fungal infections.

How to avoid mold inhalation in your home and in your garden

Like many fungi, Aspergillus thrives in decaying environments. Soil beds, compost bins, and decaying wood are plenty hospitable for fungal growth, and mold spores can become airborne and spread to new environments.

Drug-resistant Aspergillus is virtually everywhere, Rhodes said, because spores can move through the air and transfer genetic material to wild Aspergillus colonies that have never encountered azoles.

As the risk of exposure is so widespread, the authors are calling for improved surveillance of drug-resistant strains of fungus.

While the average person can’t sequence mold spores from their backyard, Rhodes recommended leaving windows open to prevent a buildup of Aspergillus in the home, as well as to clear out other pathogens like the coronavirus. N95 face masks acquired during the COVID-19 pandemic can also work for avoiding spore inhalation while gardening or handling compost.