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Indian Journal of Microbiology Research


Comparison of KOH, Calcofluor White and Fungal Culture for Diagnosing Fungal Onychomycosis in an Urban Teaching Hospital, Hyderabad


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Author Details: S. Manick Dass, Vinayaraj E. V., K. Pavavni, Aishwarya Pallam, M. Srinivas Rao

Volume : 2

Issue : 3

Online ISSN : 2394-5478

Print ISSN : 2394-546X

Article First Page : 148

Article End Page : 153


Abstract

Background and Objective: Onychomycosis is a fungal infection of the finger or toe nail apparatus caused by dermatophytes, non dermatophytemoulds and yeasts (mainly Candida species). Laboratory diagnosis of superficial fungal infection relies on direct microscopic examination of fungal elements in the clinical sample and mycological culture of the particular fungal species concerned. Quality of the sample and experience of the microbiologist are the major factors that determine the successful rate of microscopic examination and culture. All diagnostic laboratories should be able to discriminate between organisms that are likely pathogens and other contamination of the culture plate determine. A direct microscopic examination is the simplest, cheapest method used for the diagnosis of mycotic infections. In this study we want to provide detailed information on diagnosis of onychomycosis and compare the efficacy of common methods employed in microbiology laboratory. This study is valuable in establishing a reliable method for early information on diagnosis of onychomycosis that may be crucial for determining appropriate therapy for the successful treatment of onychomycosis patient.
Methodology: This is a cross sectional study conducted at Apollo General Hospital, Hyderabad. A total of 150 patients with clinical features suggestive of fungal infection were selected. All samples were subjected to KOH mount, calcofluor white and fungal culture. Sabourauds dextrose agar with chloramphenicol and cycloheximide were used for the growth of dermatophytes and incubated at 37 0 C for 3 weeks. Two tubes of SDA with chloramphenicol were used for the identification and incubated at 37 and 25 0 C for 3 weeks.
Result: Out of the 150 patients, direct microscopy with KOH mount, calcofluor mount and mycological culture showed positive results in 84(56%), 95(63.33%), 59(39.33%) respectively. Mycological culture was the least sensitive method and CFW was the most sensitive method among the 3 methods. Out of the 59 culture positive 27 were positive for Dermatophyte, 27 were non dermatophytic mould and 5 were Candida. Among non dermatophyticmould, Aspergillus was the most common isolate followed by Scopulariopsis. Culture was taken as the gold standard and when KOH mount microscopy was compared to the cul¬ture, sensitivity of KOH microscopy was 83.02% and specificity was 70.1%. When calcofluor white microscopy was compared to the cul¬ture, sensitivity of calcofluor white microscopy was 89.83 % and specificity was 60.44%.
Conclusion: In conclusion Calcofluor white is an excellent method to detect fungal agents from clinically suspected onychomycosis cases with high sensitivity and negative predictive value. It can be done in all clinically suspected onychomycosis in any laboratory having adequate technical aids. In resource poor settings, KOH mount serve as an alternative method with comparable sensitivity and negative predictive value.

Keywords: Onychomycosis, KOHmount, Calcofluor white, Trichophtonrubrum, Sabourauds dextrose agar