Mapping of inflammatory bowel disease in northern France: spatial variations and relation to affluence

Abstract

Background: Geographic variations in the incidence of inflammatory bowel disease (IBD) may reflect variations in the distribution of environmental etiologic factors. We assessed spatial variation in the incidence of IBD in northern France and analyzed its association with a deprivation index.

Methods: All cases of IBD included in the EPIMAD registry between 1990 and 2003 were extracted. The standardized incidence ratio (SIR) was calculated for each canton in the region. The association between incidence and deprivation was assessed using the Townsend deprivation index.

Results: The mean annual incidence rates of Crohn's disease (CD) and ulcerative colitis (UC) were 6.2 x 10(-5) and 3.8 x 10(-5), respectively. The mean cumulative numbers of cases by canton were 18.4 (1-183) for CD and 11.3 (0-148) for UC. For both CD and UC, mapping depicted spatial heterogeneity in the SIR with spatial autocorrelation. A high relative risk (RR) of CD was observed in mainly rural and periurban cantons of the region. For UC, a high RR was found in cantons of the south and the center of Pas-de-Calais. No significant correlation was observed between spatial variations in IBD and deprivation.

Conclusions: The incidence of IBD is associated with spatial heterogeneity in northern France. The noteworthy predominance of CD in agricultural areas warrants further investigations.