Can Foot Dermatophyte Infections Signal Future Diabetes Risk? Findings from a Register-based Study

Dermatophyte infections are common in general practice and occur more often in individuals with type 2 diabetes (T2D), but whether they signal undiagnosed T2D remains unclear. We conducted a register-based cohort study including positive PCR tests for dermatophyte infection from the feet or nails, matched 1:3 to individuals from the same geographic area in Denmark. Those with known diabetes, type 1 diabetes or aged under 20 were excluded. Incidence rates (IRs) and incidence rate ratios (IRRs) for new-onset T2D were estimated using Poisson regression. The final cohort comprised 78,140 individuals, with a median age of 51 years, and 60.8% were male. The IR for T2D was 9.23 per 100 person-years in the exposed group and 9.00 in the unexposed group, with an adjusted IRR of 1.00 (0.91-1.11, p=0.94), indicating no significant association. In a sensitivity analysis excluding unexposed individuals with prior topical antifungal treatment, the IRR increased to 1.15 (1.08-1.23, p=0.001). While the primary analysis showed no significant association, the sensitivity analysis suggested a modest increased risk when exposure misclassification was reduced, supporting dermatophyte infection as a possible early signal of undiagnosed T2D in selected populations.