Evaluation of a commercial PCR test for the diagnosis of dermatophyte nail infections

Tinea unguium, known as onychomycosis, is a dermatophyte infection of nails with worldwide distribution. Conventional methods for detecting fungi in nail specimens are either non-specific (microscopy) or insensitive (culture). PCR has been used to improve sensitivity in detecting the causative fungi in nail specimens from patients with suspected onychomycosis. Results of a commercial multiplex PCR for the detection of dermatophytes, especially Trichophyton rubrum (the main dermatophyte implicated), as compared to conventional methods are presented. A total of 418 nail scrapings obtained from dermatological outpatients were handled in the Laboratory of Microbiology between May 2010 and May 2013. Among them, multiplex PCR detected 126 (30.1%) dermatophyte-positive samples, whereas culture revealed 44 (10.5%). Direct microscopy revealed 63(15.1 %) positive specimens. T. rubrum was identified in 116 out of 126 (92%) positive PCR samples and 40 out of 44 (91%) dermatophyte-positive cultures. Implementation of PCR increased species-specific detection of dermatophytes by 21.1%, leading to a threefold increase as compared to culture alone. Multiplex PCR offers a time-saving diagnostic tool for tinea unguium and augments laboratory assistance to clinical evaluation for proper treatment.