The Incidence and Prevalence of Paediatric- and Adult-Onset Inflammatory Bowel Disease in Denmark During a 37-Year Period: A Nationwide Cohort Study (1980-2017)

Background: Incidence rates of inflammatory bowel disease [IBD] reported from developed countries are rising, with some levelling out. The aim of this study was to assess the disease burden of IBD by estimating the incidence and prevalence across age groups and projecting these to 2030 in a high-incidence country. Methods: Using an algorithm [incorporating ICD codes, medications and histopathology], patients [n = 69 862] diagnosed with Crohn's disease [CD] or ulcerative colitis [UC] between 1980 and 2017 were identified in the Danish National Patient Registry and included in a nationwide cohort. Results: From 1980 to 2017 the overall incidence of CD increased from 5.1 [95% CI: 4.5-5.8] to 15.6 [95% CI: 14.6-16.6] per 100 000, while the incidence of UC increased from 6.2 [95% CI: 5.5-6.9] to 27.2 [95% CI: 25.9-28.6] per 100 000. For paediatric-onset CD [pCD], the incidence increased from 1.9 [95% CI: 1.2-2.8] to 9.9 [95% CI: 8.1-11.8] per 100 000 and from 1.8 [95% CI: 1.2-2.8] to 8.7 [95% CI: 7.1- 10.5] per 100 000 for paediatric-onset UC [pUC]. In 2017, the prevalence of CD and UC was 293 [95% CI: 288-297] and 523 [95% CI: 517-528] per 100 000. For pCD and pUC, the prevalence was 35 [95% CI: 31-38] and 28 [95% CI: 26-32] per 100 000. Conclusions: The incidence of paediatric- and adult-onset IBD in Denmark continues to increase and is among the highest in the world.