Onychomycosis in France, SFMM survey: Laboratory practices for the diagnosis in 2023 and epidemiology in 2019-2022

Onychomycosis is a widespread superficial fungal infection worldwide, linked to dermatophytes and to a lesser extent to pseudodermatophytes or other moulds but also to yeasts. A retrospective national online survey was conducted in 2023 by the Société Française de Mycologie Médicale on the onychomycosis diagnostic process and culture identification results between 2019-2022. Among the 30 responses received for the practices part, it appeared that all laboratories used at least two culture media for this analysis (Sabouraud chloramphenicol and Sabouraud chloramphenicol-cycloheximide), 60% of them used mass spectrometry for fungal identification and 23.3% associated it with panfungal molecular sequencing. For the epidemiology part of the survey, data from 31 participants were collected. Identifications of fungal cultures from nails were obtained in 20,862 cases showing 79.8% of dermatophytes, among them 84.8% of Trichophyton rubrum. Pseudodermatophytes were responsible for 281 onychomycoses (1.4%), with 68.0% of Neoscytalidium hyalinum. This fungus was found in particular in the Martinique, a French territory in the Caribbean, where it has been reported twice as frequent as T. rubrum. Yeasts and moulds were found in 10.3% and 8.5% of the nail cultures, respectively, but the data collected for these fungi in this survey did not allow to separate onychomycosis from fungal colonisation or contamination (except Candida albicans, classically retained as a pathogen of the nails mainly from the hand). Finally, from 2015 to 2022, 24 cases of invasive fungal infections originating from nail infection were reported, including three related to dermatophytes, confirming that onychomycosis, rarely, can become life-threatening.