Early Release – Recognition of Antifungal-Resistant Dermatophytosis by Infectious Diseases Specialists, United States – Volume 30, Number 9—September 2024 – Emerging Infectious Diseases journal

Dermatophytosis (i.e., ringworm, tinea) is a common superficial fungal skin infection caused by dermatophyte molds (1). In the past decade, widespread outbreaks of antifungal-resistant dermatophytosis have occurred in South Asia because of the spread of Trichophyton indotineae fungus, which causes extensive pruritic plaques on the trunk, extremities, groin, and face in immunocompetent persons (2–4). Unlike typical dermatophyte skin infections, those involving T. indotineae fungus often do not resolve with over-the-counter topical antifungals or oral terbinafine (first-line systemic therapy) (2,3).

T. indotineae fungus has been detected in at least 11 US states, and recalcitrant dermatophytosis caused by antifungal-resistant T. rubrum fungus also has been reported (2,5,6). Affected patients have experienced diagnostic delays and received inappropriate therapies, including topical corticosteroids, which can worsen dermatophytosis (2). Antifungal-resistant dermatophytosis cases in the United States probably are underrecognized because this condition is not reportable to public health authorities in any state (https://www.cdc.gov/fungal/php/case-reporting) and most superficial fungal infections are not confirmed with diagnostic testing (7). Further, laboratory capacity to identify dermatophyte species and perform antifungal-susceptibility testing (AFST) may be limited, given that definitive identification of certain species, such as T. indotineae, requires advanced molecular techniques (e.g., using internal transcribed spacer region sequencing) and most clinical laboratories do not perform AFST for molds (2,8).

Antifungal-resistant dermatophytosis cases might require infectious diseases (ID) clinician consultation both to manage antifungal use and because of the potential effect of these infections on highly immunocompromised patients. Understanding ID clinicians’ level of awareness regarding antifungal-resistant dermatophytosis and access to laboratory testing could improve strategies to increase disease recognition and facilitate early appropriate treatment. Therefore, we surveyed ID clinicians by using the Emerging Infections Network (EIN) (https://ein.idsociety.org), a sentinel network of ID physicians and other ID specialists.

During December 2023, EIN distributed a survey link to ≈3,000 member subscribers on 3 separate occasions ≈1 week apart. EIN queries are designated as non–human subjects research by the institutional review board of the University of Iowa.

In total, we received 158 responses (Table). The most common practice setting was university hospital (47%), followed by community hospital (16%) and nonuniversity teaching hospital (12%). Most respondents were adult ID physicians (80%), followed by pediatric ID physicians (12%), pharmacists (4%), nurse practitioners, physician assistants or physician associates (1%), or other (3%). Overall, 103 (65%) respondents had heard of antifungal-resistant dermatophytosis before receiving the survey; among those, most (58%) had heard of it through previous EIN listserv emails. Seventeen percent of respondents reported seeing or consulting on a patient who had dermatophytosis that was potentially resistant to treatment or concerning for resistance within the previous year.

Approximately half (47%) of respondents reported that if they saw a patient with potentially resistant dermatophytosis, they either would not be able to obtain laboratory testing to determine the species (16%) or were unsure whether they could obtain such testing (31%) (Table). Likewise, most respondents (61%) reported they would either not be able to obtain testing to determine if a dermatophyte was resistant to antifungals (16%) or were unsure whether they could obtain such testing (45%).

In summary, our survey found that approximately one third (35%) of ID clinicians had not heard of antifungal-resistant dermatophytosis. Only 53% of respondents reported knowing how to obtain access to dermatophyte speciation testing, and even fewer (39%) reported knowing how to obtain testing for dermatophyte resistance (Table). Those findings probably reflect the relatively recent recognition of these infections in the United States and the fact that testing to identify T. indotineae and other resistant dermatophyte species is limited to select US mycology reference centers and public health laboratories (2,8).

Dermatophyte species identification and AFST are critical to guiding antifungal treatment decisions for patients with potentially resistant dermatophytosis and for monitoring population-level trends in resistance profiles to inform treatment guidelines (8). National guidelines for treating antifungal-resistant dermatophytosis are lacking, but the azole antifungal itraconazole has been used successfully for patients with dermatophytosis caused by T. indotineae and terbinafine-resistant T. rubrum fungi (2,9). However, clinicians should be aware of challenges with itraconazole, including pharmacokinetic variability (e.g., absorption), insurance coverage, drug–drug interactions, need for prolonged treatment (e.g., >6 weeks), and reports of emerging itraconazole-resistant T. indotineae and T. rubrum fungi (2,6,9,10).

One limitation of our survey is its low response rate and nonrepresentative nature. Furthermore, the survey might overestimate clinician awareness of antifungal-resistant dermatophytosis and laboratory testing access if clinicians experienced in this topic were likelier to respond. Despite those limitations, our survey highlights a need for increased awareness of antifungal-resistant dermatophytosis and increased laboratory capacity to identify and perform susceptibility testing for dermatophytes to address this emerging public health concern.

Healthcare professionals can find information about recognizing, diagnosing, treating, and reporting emerging dermatophyte infections online (https://www.aad.org/member/clinical-quality/clinical-care/emerging-diseases/dermatophytes), including information about laboratories that can perform testing (https://www.aad.org/member/clinical-quality/clinical-care/emerging-diseases/dermatophytes/recognizing-trichophyton-indotineae#testing). Those websites were developed as a collaboration between the Centers for Disease Control and Prevention and the American Academy of Dermatology’s Emerging Diseases Task Force.

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