Cyclical variation in the incidence of childhood‐onset type 1 diabetes during 40 years in Navarra (Spain)

OBJECTIVE: To trace the evolution of type 1 diabetes (T1D) in Navarre in children under 15, between 1977 and 2016, and their characteristics at onset regarding age and sex. SUBJECTS AND METHODS: We performed a descriptive analysis, using prospective-retrospective information. The study included all cases of T1D diagnosed in Navarre in children aged 0 to 14 years old from 1 January 1977 until 31 December 2016. The capture-recapture method was used, retrieving information from three independent sources: the five hospitals in Navarre as a primary source, and the Navarre Association of Diabetics (ANADI) and the primary healthcare system as the secondary source. Estimates and confidence intervals were calculated assuming a subjacent Poisson distribution. Chi square test was used to compare incidence between groups. The analysis of changes in incidence since 1977, adjusted for age group, sex and year of diagnosis, were evaluated with a multivariate Poisson regression model and joinpoint regression. RESULTS: A total of 577 cases were registered resulting in a crude incidence rate of 14.99/100 000 inhabitants-year (95% confidence interval [CI]: 13.79-16.26). From 1977, the incidence has increased in cycles, reaching an incidence rate of 22.98 (95% CI: 18.52-28.21) in 2016. The relative annual increase is 3% (95% CI: 2.3-3.8). The highest incidence is in the 10 to 14 age group (P < 0.001). No differences in sex were found. The mean age at onset in children under 15 years has not changed significantly (P = 0.572). CONCLUSIONS: The incidence of T1D in Navarre has increased 4-fold in the last four decades but is stable since 2001.