Space-time clusters of Crohn's disease in northern France

Geographical variations in Crohn's Disease incidence have been reported worldwide suggesting putative variations in the distribution of environmental risk factors. A spatial heterogeneity in standardized incidence ratios of Crohn's Disease was previously detected in northern France. Aims The goals of this study were to highlight significant atypical clusters in terms of incidence using scan statistics methodology and to study the evolution of these clusters during the study period. Subjects and methods From 1990 to 2006, the EPIMAD Registry recorded 6,472 Crohn's Disease cases distributed in 273 administrative areas of northern France. Detection of clusters used space-time scan statistics adjusted for gender and age of patients. Results Scan statistics provided identification of 18 significant clusters of two types: 14 time-constant clusters and 4 time-varying clusters. Among the fourteen time-constant clusters, 5 clusters of high incidence and 9 clusters of low incidence were detected. Among the four time-varying clusters, 3 clusters of high incidence and 1 cluster of low incidence were identified. Conclusion The existence of time-constant and time-varying clusters suggests that risk factors of Crohn's Disease are still at work in our region.