Background: Geographical and seasonal variations of type 1 diabetes (T1D) are useful for establishing the key ethio-pathogenic factors of the disease. The present work seeks to analyze the incidence rates of T1D in Navarre for the 2009-2016 period, its geographical distribution and seasonal variations in birth and diagnosis in affected persons.
Methods: Prospective study with one primary and three secondary sources. The completeness of the registry, determined using the capture-recapture method, was 96.08%. The confidence intervals of zone and onset season incidence rates were determined assuming an underlying Poisson distribution. Adjusted effect of onset age, sex, onset season and geographical area over changes in incidence rates were analyzed using a Poisson regression model. Comparison among areas was carried out after the corresponding adjustments of incidence by the indirect standardization method.
Results: Four hundred and twenty-eight new cases were detected (incidence= 8.36/100,000 inhabitants per year, CI95%: 7.58-9.19). The disease is predominant in males (63% of patients). The incidence in children under 15 years was higher than in adults (21.54, CI95%: 18.43-25.02 vs. 5.94, CI95%: 5.23-6.71; p<0.001). Incidence was highest in the four southern regions of Navarre, most of the cases being in winter and spring. No differences were found regarding birth season over incidence.
Conclusion: Navarre maintains a high T1D incidence in childhood that decreases progressively with age. Sex, age group, geographical zone and onset season are independently associated with the incidence rates observed in the study.