Clustering of childhood IDDM - Links with age and place of residence

OBJECTIVE - To improve understanding of the etiology of IDDM by analyzing spatial and space-time distribution of the incidence in children. RESEARCH DESIGN AND METHODS - Statistical tests to detect clustering were applied to a population-based register of 1,490 children (aged 0-16 years) with IDDM in Yorkshire, northern England. The Knox test analyzed clustering in space and time, and the Potthoff-Whittinghill test quantified spatial differences in incidence between small-area census units (electoral wards). The Potthoff-Whittinghill test was conditioned for childhood population density and deprivation (Townsend index). RESULTS - Both tests demonstrated clustering of IDDM in Yorkshire children. Space-time and spatial clustering is strongest in the younger children (0-4 and 5-9 years of age), even after conditioning for known associations. Clustering was more common in the county of Humberside during the years 1982-1985 and in wards of low population density (<0.26 0- to 16-year-old subjects per hectare). CONCLUSIONS - The study revealed a nonrandom space-time distribution of IDDM in children not accounted for by known covarying demographic factors. The Potthoff-Whittinghill test has not previously been applied to childhood IDDM. The new finding of strong clustering in young children is consistent with early exposure, possibly in utero, to infectious agents or localized environmental sources.