Geographical variability of the incidence of Type 1 diabetes in subjects younger than 30 years in Catalonia, Spain.

BACKGROUND AND OBJECTIVE We decided to assess the geographical variability of the incidence of Type 1 diabetes in Catalonia (Spain) in subjects younger than 30 years at onset during the period 1989-1998. The effect of sex, age at onset, periods of years, and population density was also analyzed. MATERIAL AND METHODS Data were obtained from the prospective Catalan Registry of Diabetes Mellitus. Generalized linear mixed models were used to determine the effects of the risk factors and to find out the geographical distribution. The best model was selected by the AKAIKE information criterion. RESULTS The crude incidence of type 1 diabetes in subjects younger than 30 years was 11.8/100,000/year (95% CI 11.4-12.3). The incidence was similar between males and females in the 0-14 age group. However, there was a male preponderance in young adults. The incidence did not vary annually and was not associated with population density. The incidence did not present a spatial pattern around Catalonia. There was an unstructured geographical variability. CONCLUSIONS Some regions of Catalonia displayed values of type I diabetes higher or lower than the expected incidence. Counties with extreme values of incidence were specific for each demographic group and in no case did these counties make up clusters, suggesting that there are explanatory factors with patterns of geographic distribution. The incidence of diabetes in young male adults in some counties was similar to that of European countries with a high incidence.