We analyzed all spectra identified as T. indotineae during March 2022–December 2025 by MSI users. We considered only first-intention identifications with a score of >20 (i.e., above the threshold used for the application for correct species identification as previously described [9]). When the same spectrum was uploaded multiple times, only 1 entry was retained. We addressed the bias caused by the increase in the number of users over time by normalizing the number of T. indotineae identifications relative to the number of identifications for the genus Trichophyton spp. and for the T. mentagrophytes complex (i.e., T. mentagrophytes, T. interdigitale, and T. indotineae).

Figure 1

Figure 1. Geographic distribution of Trichophyton indotineae spectra in study of global spread of T. indotineaetracked by the Mass Spectrometry Identification (MSI) Network, 2022–2025. Maps indicate global (A)...

During the study period, 566 users from 54 countries submitted 1,657,334 spectra that led to the identification of fungal agents. Those identifications included 123,025 (7.7%) that were identified as Trichophyton spp. (by 316 users in 44 countries) and 3,399 (0.2%) that were identified as T. indotineae (by 183 users in 29 countries) (Figure 1, panel A). The number of T. indotineae identifications per user ranged from 1 to 299 spectra. Europe accounted for 63.8% of users, ahead of Asia (16.8%), Latin America (15.7%), North America (1.6%), Oceania (1.6%), and Africa (0.5%). As a consequence, most T. indotineae spectra were identified in Europe (3,040 [89.4%]). In western and northern Europe, which had the highest number of MSI users, detections were not limited to major urban centers.

Figure 2

Figure 2. Temporal evolution of Trichophyton indotineae spectra identified in study of global spread of T. indotineaetracked by the Mass Spectrometry Identification Network, 2022–2025. Spectra were identified during...

Over the study period, the number of T. indotineae spectra increased continuously: from 237 in 2022 to 454 in 2023, then to 1,016 in 2024, and finally to 1,692 in 2025. At the same time, the percentage of spectra identified as T. indotineae within the Trichophyton genus increased from 1.2% to 3.6% and within the T. mentagrophytes complex from 4.6% to 13.1% (Figure 2). Among centers identifying Trichophyton spp. isolates, the percentage that detected T. indotineae rose from 24.7% to 46.1%.

Our results reveal a marked global increase in T. indotineae isolation; the number of identifications rose ≈3-fold during 2022–2025. At the same time, the proportion of T. indotineae within the T. mentagrophytes complex has increased. Those findings are consistent with national or regional data that also demonstrate a temporal increase and a wide geographic distribution. Of note, the analysis of MSI data indicates T. indotineae was identified in countries where no cases had yet been reported, such as Bulgaria, Croatia, Colombia, Luxembourg, and Uruguay. Recent publications have already demonstrated the usefulness of MSI in identifying the first cases of T. indotineae in Brazil and Hungary (10,11).

The first limitation of our study is that the picture we provide of the geographic distribution of T. indotineae reflects both the availability of mass spectrometry devices and the use of the MSI application. Thus, no spectra were identified in Africa, where the devices are not widely available, or in well-known T. indotineae–endemic areas such as India and the Middle East, where few, if any, MSI users are present. Another pitfall is that the analysis is based on the number of spectra, not on the number of isolates. Inferring the number of isolates without additional data is difficult. Moreover, we do not control the conditions under which the application is used, because MSI might be used for research purposes and not exclusively for diagnostic use. Furthermore, isolates originating from a specific geographic area might be transmitted and consequently identified in another location or even another country (e.g., when isolates are sent to reference centers or used as part of research).

However, our results demonstrate that MSI can serve as a powerful interface and epidemiologic surveillance tool for emerging fungal pathogens such as T. indotineae or Candida auris. Integration of clinical and antifungal susceptibility data could enable the development of a more complete surveillance network for T. indotineae and bolster other initiatives, such as one supported in 2023 by the European Centre for Disease Prevention and Control that encouraged reporting of T. indotineae infections through EpiPulse (https://www.ecdc.europa.eu/en/publications-data/communicable-disease-threats-report-14-17-may-2023-week-20).

In non–T. indotineae–endemic settings, distinguishing between imported and locally acquired cases is key. The establishment of T. indotineae is now well documented in eastern China (12), and, in Germany, a growing number of infections have been reported since early 2025 among patients without recent travel history, indicating local transmission (13). Similarly, increased vigilance regarding transmission routes is required to improve understanding of T. indotineae dissemination mechanisms. Sexual transmission has recently been suggested as an underestimated route, which has been seen for T. mentagrophytes ITS-genotype VII (14). Because MSI is also used in veterinary laboratories, identifying host types could help monitor the zoonotic circulation of T. indotineae, because cases have been reported in dogs in India, Iran, and Egypt (15). Reliable and rapid identification of T. indotineae has direct clinical benefits, and real-time detection of T. indotineae cases could help identify patients for inclusion in clinical trials, which are needed given the frequent relapses observed after apparent cure with itraconazole therapy

In conclusion, we encourage microbiology laboratories to use MSI to identify dermatophytes for both individual and public health benefit. Health authorities should address this rapidly evolving international issue, which is associated with therapeutic challenges.