Emerging Antifungal-Resistant Onychomycosis in a Dermatology Clinic in Kumamoto, Japan.

We examined 477 patients with culture-positive onychomycosis at the Noguchi Dermatology Clinic between July 2015 and June 2024. Toenail onychomycosis (n = 422) was caused by Trichophyton rubrum (78.0%), Trichophyton interdigitale (19.0%), non-dermatophyte mould (2.8%) and Candida species (0.2%). Fingernail onychomycosis (n = 69) was caused by Candida species (46.4%), T. rubrum (43.5%), T. interdigitale (2.9%), non-dermatophyte mould (4.3%), and Trichosporon species (2.9%). Terbinafine-resistant dermatophyte onychomycosis (n = 17) was caused by T. rubrum (94.1%) and T. interdigitale (5.9%). The prevalence was higher than in the Japanese survey (2.3%), accounting for 6.0% of cases since 2020. Ten mutant strains (58.8%) also showed reduced sensitivity to itraconazole (0.125-0.5 mg/L). These strains were highly sensitive to ravuconazole, efinaconazole, and luliconazole. Fosravuconazole (n = 13) and topical efinaconazole (n = 4) could cure the disease. Non-dermatophyte mould onychomycosis (n = 15) was caused by Aspergillus species (40.0%), Fusarium species (33.3%), Penicillium citrinum, Talaromyces muroii, Botryosphaeria dothidea, and Scopulariopsis brevicaulis (6.7%). When the breakpoint was set to 0.5 mg/L, these strains frequently exhibited resistance to terbinafine (71.4%) and itraconazole (92.9%). Efinaconazole (n = 7) and fosravuconazole (n = 5) were effective in treating these patients. Yeast onychomycosis (n = 35) mainly affected the fingernails (34/35) and was mainly caused by Candida albicans (88.6%). We identified non-albicans Candida species (n = 2), including Candida guilliermondii and Candida parapsilosis. Non-albicans Candida isolates showed low sensitivity to itraconazole and fluconazole. Trichosporon species (n = 2) were isolated from fingernail onychomycosis.