Association Between Short-Term Exposure to Fine Particulate Pollution and Outpatient Visits for Ulcerative Colitis in Beijing, China: A Time–series Study

Environmental factors play an important role in the development of ulcerative colitis (UC). However, only few studies have examined the effects of air pollution on UC occurrence. We conducted a time–series analysis to explore the association between short-term exposure to fine particulate matter (PM2.5) and outpatient visits for UC in Beijing, China. In total, 84,000 outpatient visits for UC were retrieved from the Beijing Medical Claim Data for Employees between January 1, 2010 and June 30, 2012. Measurements of daily PM2.5 concentrations were obtained from the United States Embassy air-monitoring station. A generalized additive model with quasi-Poisson link was applied to examine the association between PM2.5 concentrations and outpatient visits for UC stratified by sex, age, and season. We found that short-term exposure to PM2.5 was significantly associated with increased daily outpatient visits for UC at lag 0 day. A 10 μg/m3 increase in PM2.5 concentration at lag 0 day corresponded to a 0.32% increase in outpatient visits for UC (95% confidence interval (CI), 0.05–0.58%; P = 0.019). There was a clear concentration–response association between daily outpatient visits for UC and PM2.5 concentrations. The PM2.5 effects were significant across all sex and season subgroups, without evidence of effect modification by sex (P = 0.942) or season (P = 0.399). The association was positive in patients younger than 65 years old but negative in those 65 years old or older, although the difference was not significant (P = 0.883). In conclusion, our study demonstrated that short-term exposure to ambient PM2.5 was significantly associated with an increased risk of daily outpatient visits for UC, especially in younger people. Additional studies are warranted to confirm our findings.