Revisiting onychomycosis: Etiological agents and antifungal susceptibility profile

Onychomycosis has a prevalence varying from 2% to 8% at present. The incidence is rising day-by-day worldwide. There are only a few studies that have looked into resistance pattern of onychomycosis isolates, and so the present study was planned to study the epidemiology and mycological profile, including antifungal susceptibility testing, for patients presenting with onychomycosis. The present prospective study (January 2019 to June 2020) was conducted on a total of 92 clinically suspected patients of onychomycosis as per standard mycological techniques. Antifungal susceptibility testing (AFST) was done for itraconazole, terbinafine, griseofulvin, and amphotericin B as per Clinical Laboratory Standard Institute guidelines. Sixty-five out of 92 (70.6%) nail samples were positive for fungal aetiology on KOH examination, while 50 samples grew fungi. Nineteen (38%) were dermatophytes (95% CI: 24.6%-51.4%), while 31 (62%) of the isolates were non-dermatophytes (22 non-dermatophyte moulds, NDM [95% CI: 30.3%-57.7%]; and 9 yeast [95% CI: 7.4%-28.6%]). Onychomycosis was more common in males (55.3%) and in the age group 41-50 years. Twenty-one patients had diabetes. Great toe [40 (61.5%)] as affected nail and distal and lateral onychomycosis was the most common presentation [47(72.3%)]. Among dermatophytes, MIC range was 0.125-2 μg/ml for terbinafine, while it was 0.25-4 μg/ml for itraconazole. The MIC50 and MIC90 values were low for amphotericin B, while very high for griseofulvin. Among Aspergillus sp. and yeast isolates, minimum inhibitory concentration (MIC) range was low for terbinafine and itraconazole as 0.03-0.25μg/ml, 0.06-8μg/ml, 0.03-0.25μg/ml and 0.03-0.25 μg/ml respectively. Over the years, the treatment of onychomycosis has been shifted from griseofulvin to terbinafine and itraconazole as has been proven by the study too that MIC values for griseofulvin were very high. It is important to study and generate data regarding the prevalence and antifungal susceptibility profile of not only dermatophytes but also NDMs and yeast, which are increasingly isolated, for not only epidemiological purposes but also to plan targeted treatment at optimum doses of antifungals.