Age at diagnosis and seasonal variation in the onset of insulin-dependent diabetes in Chile (Southern hemisphere).

The age at diagnosis, sex, and the date of both the diagnosis (month--year) and the onset of symptoms of 525 insulin-depdendent diabetic patients, under 30 years of age at the time of diagnosis, were collected retrospectively from hospital records. The patients came from Chilean cities located in the Central Zone: Santiago (87%) and Temuco--Concepcion (13%). The age at diagnosis showed a bimodal distribution up to 19 years of age, with the main peak at 12 years and another at 6 years. The female peak preceded the male peak by 1 to 2 years. The onset of symptoms showed a seasonal variation, with the highest frequency in winter and the lowest in spring (P less than 0.01). There was also a significant variation in the time of diagnosis, especially in the 0--19 age group: most cases were diagnosed in winter (June, July) with the lowest number in summer (December).