Ambient air pollution correlates with hospitalizations for inflammatory bowel disease: an ecologic analysis

Known genetic loci account for less than 25% of the risk for inflammatory bowel disease (IBD), suggesting a potential role for environmental triggers. The association between ambient air pollution and IBD hospitalizations has not been previously studied.

Data from the Wisconsin Hospital Association (WHA) for the year 2002 was used to identify the number of IBD-related hospitalizations for each of the 72 counties in Wisconsin. Average annual emissions density (2002) for each of the six criteria pollutants were obtained for each county from the Environmental Protection Agency. Pearson correlation and Poisson regression analysis were performed at the level of the county.

There was a mean of 81.3 IBD hospitalizations/100,000 population per county (range 0-174). The total criteria pollutant emissions density correlated significantly with adult IBD hospitalizations (Pearson's correlation coefficient (rho) 0.28, P = 0.02). On Poisson regression, a 1-log increase in the density of total criteria pollutant emission was associated with a 40% increase in the rate of IBD hospitalizations (incidence rate ratio [IRR] 1.40, 95% confidence interval [CI] 1.31-1.50) This was similar for both ulcerative colitis (UC) (IRR 1.48, 95% CI 1.27-1.73) and Crohn's disease (CD) hospitalizations (IRR 1.39, 95% CI 1.26-1.52). Analysis of each of the individual criteria pollutant emission densities revealed a significant association for all the component criteria pollutants.

In this ecologic analysis, total air emissions of criteria pollutants appear to be associated with hospitalizations for IBD in adults. The ecologic design precludes drawing firm conclusions about association or causality and further research is needed.