Background: Questionnaire studies have been used to determine the prevalence of onychomycosis in the United Kingdom and Europe. One disadvantage of this methodology is that the patient self-diagnoses the onychomycosis. There have been very few large studies involving clinical examination of the nails of subjects, followed by mycological confirmation of the onychomycosis. We therefore determined the prevalence of onychomycosis in patients visiting dermatologists' offices in Ontario, Canada.
Methods: In a prospective, multicenter study, the finger- and toenails of all new patients presenting to dermatologists' offices were examined by a board-certified dermatologist. If there was clinical suspicion of onychomycosis, then nail samples were obtained for mycological examination at a central laboratory. Patients referred specifically for the management of onychomycosis were excluded.
Results: Toenails appeared abnormal in 455 (22.7%) of 2001 patients. Mycologically-confirmed pedal onychomycosis was present in 182 (9.1%) of the 2001 patients. The estimated value of the prevalence of onychomycosis in Ontario is 6.86% (95% confidence interval (CI): 5.8-8.0%), when corrected for age and sex of the general population using census data. Onychomycosis increased with age (P < 0.0001). The odds of males having onychomycosis was 84.3% greater than females of the same age (P = 0.0003). The distribution of organisms in the 141 patients with pedal onychomycosis who were culture positive was: dermatophytes 131 (92.9%), Candida species 4 (2.8%) and non-dermatophyte molds 6 (4.3%).
Conclusions: The prevalence of mycologically-confirmed toenail onychomycosis was 9.1%, with the estimated prevalence in Ontario being 6.86%. The majority of patients with abnormal-appearing nails were unaware they might have onychomycosis, that it is infectious and potentially treatable, suggesting that there is potential for increased public awareness and education.