Inappropriate Antifungal Prescribing May Be Driving Resistant Ringworm Infections

Jennifer Middleton, MD, MPH
Posted on February 11, 2024

A novel antifungal-resistant tinea species, Trichophyton indotineae, has been causing severe skin infections in South Asia over the last 10 years, and this species has since been identified in 11 U.S. states. Patients with T. indotineae infections can have widespread disease and often require oral antifungal medications for treatment. T. indotineae’s appearance correlates with a high incidence of topical antifungal use in the United States, prompting the Centers for Disease Control and Prevention (CDC) to recommend that physicians (1) confirm the presence of tinea before prescribing these medications and (2) eliminate the use of combination topical antifungal/corticosteroid products.

Tinea corporis, often referred to colloquially as ringworm because of its annular appearance, is a “common infection of the epidermis (skin, hair, or nails) caused by dermatophyte molds.” The differential diagnosis of tinea corporis’s classic erythematous, raised, scaly ring is extensive and includes annular psoriasis, atopic dermatitis, erythema multiforme, and granuloma annulare. Although most family physicians, podiatrists, and dermatologists are confident that they can diagnose ringworm based only on its clinical appearance, a 2017 survey found that eight out of 15 board-certified dermatologists missed the diagnosis of tinea corporis when based only on “visual inspection,” and varying proportions of survey participants also incorrectly attributed other diagnoses to tinea.

Topical antifungal medications are commonly prescribed in the United States for these infections; a recent report by the CDC found that “a total of 6.5 million topical antifungal prescriptions were filled by Part D beneficiaries (overall rate = 134.0 prescriptions per 1,000 beneficiaries)” in 2021 at a total cost of U.S. $231 million. Of those, 15% were antifungal prescriptions for clotrimazole/betamethasone dipropionate, which was of particular concern to the authors given the speculation that combination topical antifungal/corticosteroid products are a primary driver of antifungal-resistant tinea species such as T. indotineae. The authors of this report urge clinicians to instead use “antifungal monotherapy, with a short course of low-potency corticosteroid treatment added if needed for symptoms such as severe pruritis.”

A 2014 AFP article on “Diagnosis and Management of Tinea Infections” includes a detailed description of how to perform a potassium hydroxide (KOH) preparation to confirm a tinea corporis diagnosis before prescribing a topical antifungal. The article reminds readers that topical butenafine or terbinafine are more efficacious for ringworm compared with topical clotrimazole or miconazole; it also discourages the use of combination topical antifungal/corticosteroid products “because they can aggravate fungal infections.” If you are concerned that a treatment-resistant case of tinea corporis might be caused by T. indotineae, the CDC advises contacting your local public health department for assistance. Finally, we can help to curb the spread of superficial tinea infections by reminding patients to shower after exercise, not walk barefoot in locker rooms or public showers, not share sports equipment (such as helmets), and change socks and underwear at least once a day.