Objective: To verify whether the high incidence of insulin-dependent diabetes mellitus (IDDM) in Sardinia is an epidemic outbreak or a steady phenomenon.
Research design and methods: All newly diagnosed cases of IDDM with onset in patients 0-29 years of age between 1 January 1989 and 31 December 1992 among residents in Sardinia were obtained from the Sardinian IDDM Incidence Registry. The local IDDM patient association (Associazione Diabete Infantile Giovanile) served as the secondary and independent source.
Results: The completeness of ascertainment was 91%. The age-standardized mean annual incidence of IDDM (per 100,000) was 34.4 in the 0- to 14-year-old age-group and 26.2 in the entire 0- to 29-year-old range, respectively. Men-to-women ratios were 1.38 and 1.55, respectively. Seasonal variation in incidence was observed, with a peak in fall and winter and a nadir in summer.
Conclusions: Sardinia has a very high and steady IDDM incidence rate, which is up to fivefold that of other Italian regions and Mediterranean countries and approaches the Finnish top rate in the world. Interaction between the genetic peculiarity of Sardinians and still unidentified powerful environmental agents is likely to account for the phenomenon.