Prevalence, Molecular Characterization, and Antifungal Resistance of Dermatophytes Causing Onychomycosis in Adults in Kaduna, Kaduna State

Onychomycosis, a fungal infection of the nail apparatus, represents the most prevalent nail disorder globally, causing significant cosmetic, functional, and quality-of-life burden. Despite its prevalence in tropical settings, molecular epidemiological data on causative dermatophyte species and antifungal resistance in North West Nigeria are absent. This study investigated the prevalence, molecular characterization, and antifungal resistance of dermatophytes in adults with onychomycosis at a dermatology clinic in Kaduna, Kaduna State. Nail clippings and scrapings from 120 consenting adults with clinical onychomycosis were processed by direct KOH microscopy and culture on Sabouraud Dextrose Agar with cycloheximide. Species identification was confirmed by ITS region sequencing of recovered isolates. Antifungal susceptibility was determined by EUCAST broth microdilution for terbinafine, itraconazole, fluconazole, and amorolfine. Dermatophyte culture positivity was 62.5 percent. Trichophyton rubrum was the predominant species (68%), followed by T. mentagrophytes complex (19%) and T. violaceum (13%). Reduced terbinafine susceptibility (MIC above 0.125 mg/L) was detected in 11.7 percent of T. rubrum isolates, linked to SQLE gene mutations confirmed by sequencing. Itraconazole remained effective across all isolates. Advancing age, diabetes mellitus, and wearing occlusive footwear were significant risk factors. These findings provide the first molecular-level dermatophyte resistance data from North West Nigeria and support terbinafine susceptibility testing before treatment initiation. Keywords: onychomycosis, Trichophyton rubrum, ITS sequencing, terbinafine resistance, Kaduna.