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BackgroundOnychomycosis, a fungal nail infection, is primarily caused by dermatophytes, yeasts, and non-dermatophyte moulds (NDMs). The incidence of this disease and the predominance of specific pathogens vary across different regions and evolve.ObjectivesThis study aimed to elucidate the epidemiology of onychomycosis and the pattern of causative pathogens in Beijing, and to ascertain the in vitro antifungal susceptibility profiles of Trichophyton rubrum against itraconazole (ITR), terbinafine (TER), and fluconazole (FLU).Materials & MethodsInvolving 245 patients of onychomycosis with positive fungal culture results, the study implemented internal transcribed spacer (ITS) sequencing of ribosomal DNA (rDNA) on all collected samples. The mean age of the participants was 37.93 ± 13.73 years, with a male-to-female ratio of 1.53:1.ResultsThe prevalence of toenail infections was significantly higher than that of fingernails. Distal and lateral subungual onychomycosis (DLSO) were the most frequent clinical classifications. PCR results indicated that dermatophytes were the most prevalent pathogens, followed by yeasts and NDMs, among which T. rubrum was the most dominant dermatophyte.ConclusionTER demonstrated high sensitivity to T. rubrum. However, in clinical settings, some patients with onychomycosis exhibit a poor response to TER treatment. The relationship between in vitro antifungal sensitivity and clinical effectiveness is complex, and understanding the link between in vitro MIC values and clinical efficacy requires further investigation.