THE SARDINIAN IDDM STUDY - 1 - EPIDEMIOLOGY AND GEOGRAPHICAL-DISTRIBUTION OF IDDM IN SARDINIA DURING 1989 TO 1994

Analysis of the geographical variation of risk for a disease is a key issue in descriptive epidemiology and may provide useful suggestions f or planning further studies to identify the underlying causes. We adop ted a Bayesian approach to investigate the geographical distribution o f insulin-dependent diabetes mellitus (IDDM) incidence rate across Sar dinia. Data on incidence of IDDM in children aged under 15 years (619 IDDM cases) in Sardinia was obtained by the Sardinian Eurodiab ACE reg ister, The overall completeness of ascertainment was: 91.3 %. The aver age yearly standardized incidence rate for the years 1989-1994 was 33. 24 per 100000 (95 % C.I. 30.60, 35.88), which is the second highest in Europe after Finland. Sex and age-specific risks were higher in males than in females. Considering the variation of IDDM risk according to the age at diagnosis, the risk profile increased up to the 13th year o f age for both sexes, being steeper in males. The degree of geographic al variation in IDDM risk was small with a slight difference between t he highest and the lowest standardized rate across the map, Indeed, ev en the municipalities at lowest risk in Sardinia showed a risk higher than most European countries. The Sardinian population is genetically atypical, characterized by genetic homogeneity and marked susceptibili ty to autoimmune diseases. Our finding of a small geographical variati on within the island coupled with a marked temporal trend previously o bserved in data on military conscripts could be interpreted as evidenc e of a relatively recent environmental aetiological factor that was un iformly distributed across the island and had its effect in a genetica lly predisposed population.