Clinical evaluation of a dermatophyte RT-PCR assay and its impact on the turn-around-time: a prospective study.

Abstract

Onychomycosis is an important public health problem whose prevalence continues to grow and impact public health at several levels. Nevertheless, today the main diagnostic methods used in routine practice have many drawbacks. The aim of this study was to evaluate, for the first time, the clinical performance of a new multiplex PCR (Novaplex®) in the identification of the causative agent on nail samples, and its impact on the turnaround time, compared to our traditional laboratory methods. From 06/29/2022 to 12/21/2022, all nail samples sent to our laboratory for suspected onychomycosis were included in this prospective study. We collected for each sample the result obtained with the NovaplexࣨPCR method and with the traditional direct microscopy examination and culture. Each discordant result was checked using a third method, which is another PCR method (DermaGenius®kit) as resolver. For culture-positive samples, a turnaround time was calculated and compared to the one obtained with the Novaplex®method. A total of 131 samples were included. Among them, 5 were positive (3.8%) on direct microscopy, 33 positive (25.2%) after culture and 98 negative (74.8%). All positive (n=33) and negative (n=69) cultures were also positive/negative with the Novaplex®PCR. Twenty-nine samples were positive with the Novaplex®method but negative with culture (discordant results). The percentage agreement between the culture and the Novaplex® methods was 77.9% (102/131). While tested with the resolver (DermaGenius® PCR), 28 out 29 discordant results were similarly found positive. The percentage agreement between the 2 PCR methods (Novaplex® and DermaGenius®) was 96.6%. The Novaplex® PCR method evaluated proved to be very reliable and allowed the direct identification of 62/131 positive samples (47.3%) with the following distribution: 79.0% of Trichophyton rubrum complex, 11.3% of Trichophyton mentagrophytes complex, 6.5% of both Trichophyton rubrum complex and Trichophyton mentagrophytes complex and 3.2% Candida albicans. The median time [± 95% CI] for positive culture (between incubation and validation of the final identification) was 15 [12-23] days while the turnaround time for the Novaplex® method adapted to our clinical laboratory routine is ≤ 7 days. Laboratory confirmation of onychomycosis is crucial and should always be obtained before starting treatment. The evaluated PCR method offered a rapid, reliable, robust, and inexpensive method of identification of the causative agent compared to traditional methods.