The epidemiology of coeliac disease in East Dorset 1993-2002: an assessment of the 'coeliac iceberg', and preliminary evidence of case clustering.

BACKGROUND: Coeliac disease (CD) results from mucosal exposure to dietary gluten in genetically predisposed individuals, although other environmental factors may be involved. The seroprevalence of CD is approximately 1%, with a high ratio of undiagnosed to diagnosed cases, leading to the concept of a 'coeliac iceberg'. AIM: To provide contemporary estimates of the incidence of diagnosed CD and the size of the submerged 'coeliac iceberg', and to seek evidence of disease clustering. DESIGN: Prospective observational study in a defined local population. METHODS: Data were collected prospectively for all biopsy-proven cases diagnosed at Poole Hospital, 1993-2002. Age-specific incidence was calculated and point prevalence estimated for cases within the defined study zone. Evidence of disease clustering was sought using a space-time scan statistic based on a Poisson model. RESULTS: The overall incidence of CD was 8.7 cases/100,000/year (95%CI 7.4-10.1), with a median age at diagnosis of 53 years. Incidence increased progressively during the study period, and the estimated point prevalence of biopsy-proven CD rose from 0.18% to 0.4%. An area of significant space-time clustering was identified, with an incidence of 22.9 cases/100,000/year (95%CI 16.1-31.6), but there was no evidence of seasonality. DISCUSSION: The submerged component of the 'coeliac iceberg' may be diminishing due to increasing case ascertainment, with a projected ratio of undiagnosed to diagnosed cases as low as 1.5:1. Our identification of clustering must be interpreted with caution, but suggests that an additional environmental factor may influence the pathogenesis of CD.