Successive mycological nail tests for onychomycosis: a strategy to improve diagnosis efficiency

ABSTRACT

Onychomycosis is a fungal infection of nails caused by dermatophytes, yeasts and moulds, accounting for about 50 percent of onychopathies. A high frequency of onychomycosis caused by Candida species has been reported during the last few years in northeast Brazil, as well as in other regions of the world. A clinical diagnosis of onychomycosis needs to be confirmed through laboratory exams. We evaluated the importance of serial repetition of direct microscopic exams and fungal culture for the diagnosis of onychomycosis in the city of Fortaleza, Ceará, in northeast Brazil. We first made a retrospective study of 127 patients with onychomycosis, identifying the fungi that had been isolated from fingernails and toenails. We then made a prospective study of 120 patients, who were submitted to three successive mycological examinations. Ungual residues were scraped off and directly examined with a microscope and fungal cultures were made. In the retrospective study, in which only one sample was analyzed, the incidence of onychomycosis was 25.0 percent. In our prospective study, in which we had data from successive mycological examinations, 37.8 percent had onychomycosis. The most commonly isolated fungi in both studies were yeasts from the genera Candida, especially C albicans, C. parapsilosis and C. tropicalis. We found a high proportion of onychomycosis caused by Candida species. We also concluded that serial repetition of direct microscopic examination and fungal culture, with intervals of 2-5 days improved the diagnosis of onychomycosis. We suggest that this laboratorial strategy is necessary for accurate diagnosis of this type of mycosis, especially when the standard procedures fail to diagnose fungal infection, despite strong clinical suspicion.