A recent study highlighted growing concerns within the dermatological community regarding an increase in treatment-resistant fungal strains.

Researchers from The University of Texas Health Science Center at San Antonio focused their investigation on dermatophytes, a group of fungi responsible for dermatophytosis, the most prevalent fungal infection globally affecting the skin, hair, or nails. The study, published in the Journal of Clinical Microbiology, looked at samples from 2021 to 2022. According to the authors, nearly 19% of dermatophyte isolates showed high resistance to terbinafine. Half of the resistant strains were identified as the common Trichophyton rubrum, while the remainder consisted of Trichophyton indotineae (T. indotineae), a novel species.

“It was about the end of 2021, beginning of 2022, we started to notice some results that were a little strange. We hadn’t seen this before,” Nathan Wiederhold, PharmD, director of the Fungus Testing Laboratory at UT Health Science Center San Antonio, said in a press release.

The rise in cultures of dermatophytes displaying resistance to the antifungal terbinafine prompted collaboration with the Mycotic Diseases Branch at the Centers for Disease Control and Prevention (CDC), which had also observed a similar trend internationally. The study results suggest T. indotineae is widespread in the United States and some Canadian provinces, according to the authors. The emergence of resistance in T. rubrum, they noted, was partly attributed to the widespread availability of over-the-counter products containing antifungals, antibiotics, and steroids.

“It’s the availability of these products that contain an antifungal, antibiotic, and they also contain steroids," Dr. Wiederhold said. "There is widespread availability in products that can be obtained without a prescription. Steroids are kind of like throwing gasoline onto a fire when you’re talking about fungal infections.” 

The CDC currently advocates for public and medical education on fungal infections and supports the development of rapid tests capable of identifying both fungus type and resistance type. The commercial availability of these tests in the U.S. remains limited pending FDA approval, however. 

“It’s now in our backyard. Education is going to be a very important thing,” Dr. Wiederhold added. 

Source: University of Texas Health Science Center San Antonio press release. Published May 10, 2024.