Supplementary Material for: Risk Factors for the Development of Fistulae and Stenoses in Crohn Disease Patients in the Swiss Inflammatory Bowel Disease Cohort

<p><b><i>Background:</i></b> Fistulae and stenoses represent frequent and severe complications in patients with Crohn disease (CD). Our study aimed to identify risk factors for fistula and stenosis formation in CD patients. <b><i>Summary:</i></b> We retrieved data of 1,600 CD patients from the nationwide Swiss Inflammatory Bowel Disease Cohort Study (SIBDCS). The risk for fistulae and stenoses in relation to gender, age at diagnosis, smoking status at diagnosis, and ileal involvement at diagnosis were analyzed. In the multivariate analysis, female gender showed a lower risk for developing perianal and any fistula (risk ratio [RR] 0.721, 95% confidence interval [CI] 0.582-0.893, <i>p</i> = 0.003 and RR 0.717, 95% CI 0.580-0.888, <i>p</i> = 0.002, respectively), and older age at diagnosis showed a lower risk for developing perianal fistula (RR 0.661, 95% CI 0.439-0.995, <i>p</i> = 0.047). Furthermore, ileal involvement was associated with a lower risk for perianal fistula (RR 0.713, 95% CI 0.561-0.906, <i>p</i> = 0.006), a lower risk for any fistula (RR 0.709, 95% CI 0.558-0.901, <i>p</i> = 0.005), and a higher risk for stenosis (RR 2.170, 95% CI 1.728-2.725, <i>p</i> < 0.001). <b><i>Key Messages:</i></b> In the nationwide SIBDCS, younger age at diagnosis and male gender were risk factors for developing perianal and nonperianal fistulae. Additionally, ileal involvement was revealed to be a potent risk factor (RR 2.170) for developing a stenosis.</p>