Development and Clinical Detection of Rapid Molecular Diagnostic System for Pathogenic Dermatophytes of Tinea Capitis of Multiple Centres in China.

Objectives: Tinea capitis remains a common fungal infection in children worldwide. Species identification is critical for determining the source of infection and reducing transmission. In conventional methods, macro- and microscopic analysis is time-consuming and results in slow fungal growth or low specificity. We propose a rapid real-time diagnostic PCR method that allows species-specific identification of dermatophytes, including the Microsporum canis complex, Trichophyton mentagrophytes complex, Trichophyton rubrum complex and Trichophyton tonsurans, in patients with tinea capitis.

Methods: Hair and scrapings samples were collected from 231 patients with tinea capitis who were positive for fungal elements via direct microscopy with potassium hydroxide. Each sample was subjected to a two-step real-time PCR (RT-PCR) assay, which was designed on the basis of differences in the DNA fragments of the internal transcribed spacer (ITS) and β-tubulin covering the Microsporum canis complex, T. mentagrophyte complex, T. rubrum complex, T. tonsurans, T. verrucosum, T. schoenleinii and N. gypseum.

Results: In total, 186/231 samples (80.52%) were positive for fungal culture. The two-step RT-PCR was positive in 215/231 samples (93.07%), among which 179 were culture positive. The combined efficacy was 96.81%, which was significantly different when the RT-PCR assays were performed in parallel with fungal culture. A total of 126 samples (54.55%) were identified as Microsporum canis by fungal culture, among which the positive rate of M. canis complex RT-PCR was 97.62% (123/126). A total of 45 samples were negative for fungal culture, of which 80.0% (36/45) were positive by RT-PCR, and the percentage of M. canis complex-positive samples was 53.33% (24/45). The RT-PCR assays were negative for 16/231 samples, among which 7 were culture positive, including M. canis (n = 3), T. violaceum (n = 3) and N. gypseum (n = 1).

Conclusion: We developed a new diagnostic assay system using a rapid real-time TaqMan PCR assay with specific primers that can be applied in routine laboratory practice for hair and skin samples of tinea capitis to detect dermatophytes and increase diagnostic efficiency.