Recalcitrant and recurrent tinea: Lessons from an international survey

Abstract

We have read with great interest the article by Khan et al.,¹ which presents the results of an international survey conducted among dermatologists on the occurrence of recalcitrant or recurrent tinea of glabrous skin. The survey, carried out between February 2022 and July 2023, focussed on cases diagnosed over the past 3 years. It complements a previous survey that was limited to the European continent, which was consequently excluded from this article.

While non-microbiological causes of treatment failure and antifungal resistance in species such as Trichophyton rubrum should not be overlooked, Trichophyton indotineae is likely the predominant cause of treatment failure on a global scale. Since the mid-2010s, Indian dermatologists have reported a rise in recalcitrant and recurrent tinea cases linked to T. mentagrophytes complex isolates, later reclassified as T. indotineae.² This fungus has now been described across all continents.^2-4 In India, resistance to terbinafine has been documented in up to 75.0% of isolates, while high minimum inhibitory concentrations to azoles are observed in approximately 25.0% of cases.⁵

Several key points in the study by Khan et al. caught our attention.

A striking finding is that the vast majority of surveyed dermatologists reported encountering recalcitrant tinea. As expected, 93% of Indian dermatologists noted such cases; however, 86.3% of non-Indian dermatologists did as well, with 42.6% reporting more than 20 cases. These figures strongly suggest that recalcitrant tinea is a global health concern warranting close attention.

Dermatologists reporting the highest numbers of recalcitrant tinea cases were primarily based in India, neighbouring South Asian countries, and Middle Eastern nations—from Israel and Lebanon to the Persian Gulf. This supports the hypothesis that T. indotineae is widely distributed across the Middle East, where it was already well-documented as early as 2008–2010 in Iran and subsequently in Iraq.²

Interestingly, Mexico was also among the countries where dermatologists reported having seen a high number of cases. Currently, very little data are available on T. indotineae in Latin America. A noteworthy case was reported in Argentina, involving a patient who likely contracted the infection in Mexico, raising questions about the circulation of the dermatophyte in the region.³

Data on T. indotineae in Africa are also extremely limited,⁴ and only a small number of African countries participated in this survey. Given the relative scarcity of data compared with other regions—along with the potential for widespread dissemination due to hot climates and healthcare disparities—Latin American and African countries should be prioritized for epidemiological research.

Another striking observation is the rarity of mycological documentation: T. indotineae was mentioned only once in the survey, and antifungal resistance was documented in fewer than 10% of cases. This underscores major challenges in accessing microbiological diagnostics, which hampers accurate assessment of global resistance patterns and complicates patient management. It is therefore essential to emphasize that methods have been developed to facilitate species identification and resistance detection.² In particular, we highlight the value of MALDI-TOF mass spectrometry, when using updated libraries such as MSI-2, as a valuable diagnostic and epidemiological tool.⁶

We fully support the authors' call for international initiatives to enhance the epidemiological documentation of T. indotineae and terbinafine resistance. Robust surveillance systems are essential for tracking trends over time and differentiating between imported cases and autochthonous transmission, as each requires distinct public health responses. Notably, autochthonous cases of T. indotineae have now been well-documented in eastern China.⁷ Furthermore, clinical trials are crucial for optimizing therapeutic strategies against this emerging pathogen.

A.J. is involved in the development of MSI-2, which is a free web application for MALDI-TOF spectra identification. No financial gain is made from its use. G.M. has nothing to declare.