A report by the US Centers for Disease Control and Prevention claims antifungal creams and combinations of antifungal treatments with corticosteroids are likely to be contributing to the rise and spread of severe skin, scalp, and nail fungal infections.

In 2023, dermatologists detected the first known cases in the US of highly contagious drug-resistant fungal skin infections that don't respond to the few fungal treatments we have.

First concentrated in Southeast Asia, these drug-resistant fungal infections have spread to China and beyond, and have now been detected in at least 11 US states to date.

To get a handle on the situation, researchers at the US Centers for Disease Control and Prevention (CDC) have examined a whole year's worth of antifungal prescriptions in the US, to understand which types of clinicians are dishing out what drugs.

As with the rise of antibiotic resistance among bacteria, overuse of antifungals gives potentially pathogenic fungi ample opportunity to find ways to thwart the drugs, especially when they are prescribed for the type of wrong infection or not used properly.

By understanding antifungal prescribing practices, CDC epidemiologist Kaitlin Benedict and colleagues hoped they could provide crucial insights to help nip the problem in the bud before it gets much worse.

"The large volume of topical antifungal prescriptions in the context of emerging resistance highlights the need to better understand current prescribing practices and to encourage judicious prescribing by clinicians and improve patient education about recommended use," the team writes in their paper.

They analyzed data on roughly 1 million health professionals who wrote prescriptions for nearly 49 million people covered under Medicare, the US government's national health insurance program, in 2021.

Roughly 6.5 million topical antifungal prescriptions were filled that year in the US, at a total cost of US$231 million, the researchers found.

"The actual volume of topical antifungal use among the study population is likely considerably higher than that identified in this study because most topical antifungals can be purchased over the counter without a prescription," the researchers note.

Most antifungal prescriptions in 2021 were written by primary care physicians (40 percent) followed by nurse practitioners, dermatologists, and podiatrists.

The top 10 percent of antifungal prescribers – some 13,106 practitioners – prescribed nearly one-half of the dispensed medications, which may be because they see a lot of patients with suspected fungal infections or are quick to treat them.

While this is suggestive of some potential overuse or at least liberal prescribing, the Medicare data didn't include diagnostic information on the types of fungal infections patients had, so the researchers couldn't determine if patients had been prescribed the right medication to treat their specific condition, or if doctors had tested the infections first to know which drug to prescribe.

Concerning Benedict and colleagues was the large number of clotrimazole-betamethasone prescriptions, which accounted for 15 percent of all topical antifungals prescribed. This combination treatment is thought to be a potential driver of emerging drug-resistant tinea, also known as dermatophytosis.

They also note how clinicians, including board-certified dermatologists, commonly diagnose a skin condition simply by looking at it, yet they are "frequently incorrect".

"To help control the emergence and spread of antimicrobial resistant superficial fungal infections and help promote the appropriateness of topical antifungal prescribing, health care providers could use diagnostic testing whenever possible to confirm suspected superficial fungal infections," the researchers conclude.

The research has been published in US CDC's journal, Morbidity and Mortality Weekly Report.