Space-time clustering in insulin-dependent diabetes mellitus (IDDM) in south-east Sweden.

Using the method developed by Knox, space-time clustering was analysed in all 584 cases of insulin-dependent diabetes mellitus (IDDM) diagnosed between 1977-1990 and below the age of 16 from four paediatric departments in south-east Sweden. The catchment areas of these clinics form a contiguous geographical area of 26,445 km2 with a total of 165,784 children aged 0-15 years. The annual incidence for the study period was 25.2 per 100,000 children aged 0-15 years with a statistically significant incidence variation between the years; highest incidence in 1983 (39.2) and lowest in 1977 and 1989 (18.9 and 20.7 respectively). In the analysis, 30 different combinations of critical cutoff values were used to define closeness in space and time of pairs of cases. Statistically significant results were seen for several combinations with the highest significance obtained for the cutoff values of 15 km and 7 months, respectively. This space-time clustering tended to be specially pronounced during the period with the highest incidence of IDDM, 1981-1985. Our results indicate that space-time clustering exists in IDDM. These findings may support the hypothesis that infectious agents (possibly viral) give rise to a portion of IDDM.