A Novel Contrast Stain for the Rapid Diagnosis of Dermatophytoses: A Cross-Sectional Comparative Study of Chicago Sky Blue 6B Stain, Potassium Hydroxide Mount and Culture

BACKGROUND: The current upsurge of complicated dermatophytosis in India and other parts of the world has necessitated the development of rapid and accurate diagnostic techniques. Conventional methods such as potassium hydroxide (KOH) mount lack color contrast and require a trained eye, whereas fungal culture is laborious and costly. Chicago sky blue 6B (CSB) a new contrast stain promises to be a reliable and rapid diagnostic method. It contains 1% CSB stain and is used with 10% KOH as clearing agent. AIMS AND OBJECTIVES: The objective of this study is to compare the efficacy of a novel contrast stain (CSB) and KOH mount in the diagnosis of dermatophytoses with culture as the reference method. METHODS: The infected skin scrapings, nail clippings, and hair specimens from 100 patients, with clinically diagnosed dermatophytoses, were subjected to KOH mount, CSB stain, and culture on Sabouraud's dextrose agar. Using fungal culture as the reference standard, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of CSB stain and KOH mount were determined. An inter-rater reliability analysis was performed using the Cohen's κ statistic to determine agreement amongst the different diagnostic modalities. RESULTS: Of the 100 cases, the CSB stain and KOH mount were positive in 85 (85%) and 70 (70%) cases, respectively. Cultures on Sabouraud's agar yielded growth in 59 (59%) cases. The sensitivity, specificity, PPV, NPV, and accuracy of CSB stain were 98%, 34%, 68%, 93%, and 72%, respectively. The same for KOH mount were 71%, 32%, 60%, 43%, and 55%, respectively. CONCLUSION: CSB stain is a simple, rapid, sensitive, accurate, and inexpensive office-based method with qualitatively superior demonstration of dermatophytes compared to KOH mount.