From the Guidelines
The most likely causative fungus in onychomycosis is dermatophyte fungi, particularly Trichophyton rubrum, which accounts for approximately 70% of all cases. This is based on the evidence from the British Association of Dermatologists' guidelines for the management of onychomycosis 2014, which states that dermatophyte infection, mostly due to Trichophyton rubrum, is the cause in over 90% of cases 1. Other common dermatophytes include Trichophyton mentagrophytes and Epidermophyton floccosum. These fungi invade the nail plate, nail bed, and surrounding tissues, causing the characteristic thickening, discoloration, and brittleness of infected nails.
Some key points to consider when diagnosing and treating onychomycosis include:
- Non-dermatophyte molds such as Scopulariopsis brevicaulis, Fusarium species, and Aspergillus species can also cause onychomycosis but are less common, accounting for about 10-20% of cases 1.
- Yeasts, particularly Candida species, are another potential cause, especially in fingernail infections and in immunocompromised individuals.
- Diagnosis typically requires microscopic examination of nail clippings with potassium hydroxide preparation and fungal culture to identify the specific causative organism, which helps guide appropriate antifungal therapy.
- The choice of antifungal therapy depends on the causative organism, with terbinafine being more efficacious than itraconazole for onychomycosis caused by dermatophytes, but itraconazole having broader antimicrobial coverage for Candida and nondermatophyte moulds 1.
Overall, dermatophyte fungi, particularly Trichophyton rubrum, are the most common cause of onychomycosis, and diagnosis and treatment should be guided by the specific causative organism and the severity of the infection.
From the Research
Causative Fungus in Onychomycosis
The most likely causative fungus in onychomycosis is:
- Trichophyton rubrum, as it is the most frequently isolated dermatophyte in onychomycosis cases 2, 3, 4, 5, 6
Types of Fungi Causing Onychomycosis
Onychomycosis can be caused by:
- Dermatophytes, primarily Trichophyton rubrum, T. interdigitale, Epidermophyton floccosum, and T. tonsurans 2, 3, 4, 5, 6
- Yeasts, such as Candida albicans and Candida parapsilosis 2, 3, 4, 5, 6
- Non-dermatophyte molds (NDM), including Fusarium species, Onychocola canadensis, and Aspergillus spp. 2, 3, 5, 6
Prevalence of Causative Fungi
The prevalence of causative fungi in onychomycosis is: