Microbiological culture combined with PCR for the diagnosis of onychomycosis: Descriptive analysis of 121 patients

Abstract

Background: Onychomycosis is the most common nail pathology, involving various pathogens such as dermatophytes, moulds and yeasts.

Objective: The objective of this study was to observe the prevalence of onychomycosis, analyse the most appropriate diagnostic test, and assess the distribution of pathogens based on age, sex, quarter of the year, duration of symptoms and previous treatment.

Methods: Retrospectively, mycological culture and PCR data and results were collected from 121 patients.

Results: Of the 121 samples, 57% (69/121) tested positive when both microbiological study techniques were combined. The prevalence of onychomycosis was higher when PCR was performed (52.1%) compared to microbiological culture (33.1%). Among the 81 samples negative by microbiological culture, 31 were positive by PCR. Similarly, of the 58 samples negative by PCR, eight were positive by microbiological culture. Diagnostic accuracy data (with 95% confidence intervals) for PCR, using microbiological culture as the gold standard, were as follows: sensitivity of 0.8, specificity of 0.62, positive predictive value of 0.51 and negative predictive value of 0.86. The most frequently identified pathogen was Trichophyton rubrum, and the hallux nail plate was the most commonly affected location. However, no statistically significant associations were found between sex, age, quarter of the year and affected area with culture and PCR results.

Conclusion: Combining microbiological culture and PCR can increase the detection rate of onychomycosis and help avoid false-negative results.

Keywords: diagnosis; microbiological culture; nail pathology and dermatophytes; onychomycosis; polymerase chain reaction.