Implementation of a multiplex real-time PCR assay in the diagnostic algorithm of dermatophytoses in Liège (Belgium)

Objectives:
Our study aimed to evaluate the contribution of the DermaGenius® PCR assay (DG PCR) in the diagnostic algorithm of fungal infections of the skin, hair and nails, at the National Reference Center for Mycosis (NRC) of Liège, Belgium.

Methods:
The study was conducted by the NRC of the University Hospital of Liège (CHU Liège) from July to October 2017. Samples (skin, hair and nails) were collected from patients consulting in the dermatology department. They were examined by histology and cultured on Sabouraud agar medium. DG PCR (Pathonostics, The Netherlands) is a commercial pan-dermatophyte real-time PCR which detects the most frequent dermatophytes and also Candida albicans. DG PCR was performed directly on samples with a positive histology but a negative culture for dermatophytes. Epidemiological data were recorded in patient medical files. Statistical analysis was applied using the Fisher’s exact test.

Results:
A total of 667 samples were included in the study period: 411 (61.6%) finger and toenails, 197 (29.5%) skin and 59 (8.8%) hair samples. Histology was positive in 243/667 samples (36%) while dermatophytes culture was positive in 178/667 (26.7%) cases. DG PCR was applied to 119 histology-positive/culture-negative samples. A total of 63/119 cases (53%) representing 9.4% of the total samples were detected which is a significant increase in the detection rate (p=0.019). Three dermatophytes species were detected by DG PCR: T. rubrum (51/63, 81%), T. interdigitale (6/63, 9.5%) and T. tonsurans (1/63, 1.6%). One co-infection T. rubrum-C. albicans and 4 C. albicans alone were also detected. Non-dermatophytes molds (NDM) were isolated in 109/667 (16.3%) samples and were present in 27/63 (43%) DG PCR positive cases attesting that dermatophytes detection was not impacted by the presence of other fungi (p= 0.722).

Conclusion:
This study demonstrates that DG PCR is an effective molecular diagnostic test allowing the direct detection of the most often encountered dermatophytes and C. albicans in skin, hair and nails samples. This PCR assay improves significantly the diagnostic efficacy of conventional tests and is able to unmask the presence of non growing dermatophytes even in presence of NDM. The implementation of molecular tests in routine diagnostics will probably reduce the role attributed to NDM in onychomycosis