Abstract Background Crohn’s disease (CD) and ulcerative colitis (UC) are chronic inflammatory bowel diseases (IBDs) with complex and multifactorial etiologies. Genetic factors have been identified but cannot fully account for disease incidence. Spatial heterogeneity in IBD incidence has been reported across various countries and scales, suggesting a significant influence of environmental factors. Leveraging the population-based EPIMAD registry in northern France (6 million inhabitants), this study aimed to analyze the spatial distribution of CD and UC incidence and identify potential environmental risk factors at a territorial level. Methods This ecological study was conducted at the municipal level across 3,041 municipalities within the EPIMAD registry's area for the period 2000-2017. Incident cases included 9,019 CD and 5,789 UC patients. Spatio-temporal age- and sex-standardized incidence ratios were modeled using Bayesian hierarchical models. An inventory of open-access environmental data sources identified 128 datasets, 19 of which were selected to generate 112 indicators at the municipal level. These indicators included contamination levels (air, water, soil), proximity to emission sources (e.g., industrial sites), land use, agricultural practices, natural features, and climate. Ecological regressions were used to explore associations between environmental indicators and incidence. Results Significant spatial disparities in CD and UC incidence were observed, remaining stable over time (Figure 1). For both CD and UC, associations were found with certain types of crops (e.g., sugar beets, barley, wheat, flax, and potatoes) and several metals in soil (e.g., molybdenum, nickel). Associations were more pronounced for CD, including strong links with pesticide use indicators (growth regulators, herbicides, fungicides) and soil contamination by other metals such as arsenic, cadmium, and thallium. For UC, a unique association was observed with soil contamination by polycyclic aromatic hydrocarbons (PAHs), while no significant association with pesticide use was found. Conclusion These findings highlight a relationship between IBD incidence and agricultural practices, providing new insights to the existing literature. Multivariate approaches should be employed to better describe environmental exposure profiles. Additionally, individual-level epidemiological studies are needed to confirm and expand upon these results.
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