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P318. Mapping of Crohn's disease in Northern France: Spatial and temporal variations of incidence between 1990 and 2006

M. Genin1, C. Gower-Rousseau1, G. Savoye2, J. Dupas3, F. Vasseur1, V. Merle2, E. Lerebours2, J. Salleron1, A. Cortot1, J. Salomez1, C. Préda1, J. Colombel1

1Hospital and University, Lille, France; 2Hospital and University, Rouen, France; 3Hospital and University, Amiens, France

Geographical variations of Crohn's Disease (CD) incidence have been reported worldwide reflecting putative variations in the distribution of environmental factors. In Northern France we were able to detect spatial heterogeneity in standardized incidence ratio (SIR) of CD [1].

The aims of this study were: (a) to confirm these results using Scan Statistics Methods [2]; (b) to highlight atypical geographic areas (clusters) in terms of incidence (low or high) between 1990 and 2006; (c) to study the variability of these clusters during the study period and (d) to compare CD phenotype at diagnosis between these clusters.

Patients and Methods: Between 1990 and 2006, 6234 CD cases were recorded by the EPIMAD Registry of Northern France distributed in 273 cantons (smallest French administrative areas) of Departements of Nord, Pas-de-Calais, Somme and Seine-Maritime (5.79×106 inhabitants). Detection of clusters used Scan Statistics based on Poisson's models using the canton for geographical unit and adjusted for gender and age of patients.

Results: Between 1990 and 2006 the mean crude annual CD incidence rate was 6.2/105 inhabitants for the whole region. Scan Statistics confirmed spatial heterogeneity of CD incidence and found 15 clusters: 8 with a significantly higher CD incidence rate (RR: 1.4–10.1) and 7 with lower (RR < 0.5) (Figure 1). These clusters have evolved over time as two major clusters with high incidence appeared in Southern region; the first appeared around 1996 and currently persists; the second recently appeared in North-western region since 2000. No difference was found between high and low clusters as far as CD characteristics and phenotypes.

Conclusions: Spatial heterogeneity of CD incidence in Northern France was confirmed. Moreover, this study isolated 15 atypical geographic areas in terms of incidence. Modifications between 1990 and 2006 suggest an evolution of risk factors in our region, thus focusing research on environmental risk factors for CD.

Figure: Relative risk of Crohn's disease in northern France (1990–2006) – spatial analysis.