Introduction

Some epidemiological studies suggest that long-term exposure to environmental air pollutants, such as particulate matter (PM), could have a role in inflammatory bowel disease (IBD) incidence and pathogenesis. However, less is known about the potential effect of short-term air pollution exposure. The aim of this study is to investigate whether short-term exposure to environmental air pollution is associated with the occurrence of IBD flares.

Aims & Methods

Anonymized hospital discharge records (HDR) with ICD-9-CM codes 555 (Crohn’s disease) and 556 (ulcerative colitis) for years 2002-2009 from all hospitals of the Lombardy region were collected. All HDR of adult patients (18-75 years) resident in Milan were included, except for recurrent hospitalizations within 6 months. Each record was assigned daily PM ≤10 µm (PM10) concentrations at municipality level by averaging PM10 levels of the day of admission with the levels of the day before (lag01) and of each preceding day up to six days before (lag06). To evaluate the association between PM10 and IBD-related hospitalizations, a time-stratified case-crossover study design was applied. Conditional logistic regression models, calculating Odds Ratios (OR) and 95% Confidence Intervals (95%CI) per increments of 10 µg/m3 of PM10, were performed.

Results

Overall, 2,176 hospital admissions (males=1,137, Crohn’s disease=1,264, ulcerative colitis=912) were included. In the entire population no clear association between PM10 and IBD-related hospitalization was identified, notwithstanding a small risk increase for males (OR: 1.03; 95%CI: 0.99-1.08 at lag04). When further stratifying for ICD code, an increased risk of hospitalization for "left-sided ulcerative colitis" (ICD code: 556.5) was found in males only, for exposures in all days preceding hospitalization up to lag04 (1.28; 1.05-1.28; 59 cases, 207 controls) (Figure 1). In females, the association was weaker, although positive (1.14; 0.91-1.42; 49 cases, 164 controls). No relevant findings emerged when looking at other ICD codes.

Conclusion

We observed an increased risk of IBD-related hospitalization in male patients with left-sided ulcerative colitis per increasing levels of air pollution in the days preceding hospital admission. Although preliminary, our findings suggest the possible role of sex as an effect modifier of the influence that air pollution might exert on IBD flares. Further studies are needed to better comprehend the complex framework characterizing the interplay between environmental and individual factors contributing to IBD.

Disclosure

DN received unrestricted research grants from Pfizer, consulting fees Dr. Falk, and lecturer fees from Ferring. MV served as a consultant for Abbvie, MSD, Takeda, Janssen-Cilag, and Celgene. He received lecturer fees from Abbvie, Ferring, Takeda, MSD, Janssen-Cilag, and Zambon. MA received consulting fees from Nikkiso Europe, Mundipharma, Janssen, Abbvie, Ferring, Galapagos, and Pfizer. FCa has served as consultant for Mundipharma, AbbVie, MSD, Takeda, Janssen, Roche, and Celgene; received lecture fees from AbbVie, Ferring, Takeda, Allergy Therapeutics, and Janssen; and received unrestricted research grants from Giuliani, SOFAR, MS&D, Takeda, Pfizer, and AbbVie.