Revisiting Onychomycosis: Etiological agents and Antifungal susceptibility profile

Abstract Onychomycosis has a prevalence varying from 2- 8% at present. The incidence is rising day-by-day worldwide. There are only few studies which 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. 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 etiology on KOH examination while fifty samples grew fungi. Nineteen (38%) were dermatophytes (95% CI: 24.6–51.4%) while 31 (62%) of the isolates were non- dermatophytes (22 non- dermatophytes molds, NDM (95% CI: 30.3–57.7%); and 9 yeast (95% CI: 7.4–28.6%). Onychomycosis was more in males (55.3%) and in age group 41-50 years. Twenty one patients had diabetes. Great toe 40 (61.5%) as affected nail and DLSO (Distal and lateral onychomycosis) was most common presentation 47(72.3%). Among dermatophytes, MIC range was 0.125 -2 μg/ml for terbinafine while it was 0.25-4μg/ml for itraconazole. The MIC50 and MIC90 values were low for amphotericin B while very high for griseofulvin. Among Aspergillus sp and yeast isolates, MIC range was low for terbinafine and itraconazole as 0.03-0.25 μg/ml, 0.06-8 μg/ml, 0.03-0.25 μg/ml, 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.