Cases were identified according to
discharge ICD-9 codes; zip codes were used to identify county, and
pollution data were obtained from the US Environmental Protection
Agency. Total criteria pollutant emission density correlated with
adult IBD admissions (rho 0.28; p=0.02) with a 40% (95% CI 1.31–1.5)
increase in hospitalization for every log increase in pollutants.2