Comparison of fluorescent staining versus KOH wet-mount microscopy for detection of superficial fungal infection

Abstract

Objective To compare the diagnostic value of fluorescent staining versus KOH wet-mount microscopy in detecting superficial fungal infection. Methods Totally, 600 specimens from cases of clinically diagnosed superficial fungal infections and 102 from cases of clinically diagnosed Malassezia infection (including 54 cases of pityriasis versicolor and 48 cases of Malassezia folliculitis) were collected from the dermatology clinic of Tenth People′s Hospital of Tongji University between July 2017 and February 2018. These specimens were subjected to fluorescent staining and KOH wet mount separately followed by direct microscopy, and the positive rate and average time for slide reading were compared between the two methods. Culture served as the gold standard method, and the missed diagnosis rate was compared between the two methods. Statistical analysis was carried out using chi-square test or Fisher′s exact test for comparing enumeration data, and paired t test for comparing emeasurement data. Results Of the 600 specimens from clinically diagnosed superficial fungal infection cases, fungi were detected in 546 (91.00%) and 489 (81.50%) by fluorescent staining and KOH wet-mount microscopy respectively (χ2 = 22.83, P 0.05) , with the average reading time being 38.36 ± 8.79 s and 41.25 ± 15.67 s respectively (t = 1.14, P > 0.05) . Of the 48 specimens from Malassezia infection cases, 43 (89.58%) and 11 (22.92%) specimens were detected to be positive for fungi by fluorescent staining and KOH wet-mount microscopy respectively (χ2 = 43.34, P < 0.05) , and fluorescent staining showed shorter average reading time (42.14 ± 12.61 s) compared with KOH wet-mount microscopy (103.56 ± 9.48 s, t = 17.83, P < 0.05) . Among the 600 specimens from superficial fungal infection cases, culture yielded fungi in 479. Moreover, 476 specimens were found positive by fluorescent staining, and 3 were found negative (0.63%) , while KOH wet-mount microscopy showed 465 positive results and 14 negative results (2.92%) . There was a significant difference in the missed diagnosis rate between the two methods (χ2 = 7.25, P < 0.05) . Conclusion Compared with KOH wet-mount microscopy, fluorescent staining can increase the detection rate, reduce missed diagnosis rate and shorten reading time. Key words: Tinea; Tinea versicolor; Malassezia; Clinical laboratory techniques; Fluorescent staining; KOH method