Incidence, disease burden and clinical presentation of patients newly diagnosed with inflammatory bowel disease in a population-based inception cohort.

Background and aims: Emerging data indicate a stabilizing incidence of inflammatory bowel diseases (IBD), including ulcerative colitis (UC), Crohn's disease (CD), and IBD unclassified (IBDU) in Western countries. We aimed to investigate the incidence of IBD, its initial clinical presentation, and patient-reported burden.

Methods: Copenhagen IBD Inception Cohort is a prospective, population-based cohort of patients with newly diagnosed IBD according to the ECCO guidelines in the period between May 2021 and May 2023, within a catchment area covering 20% of the Danish population.

Results: Based on 554 patients (UC: 308, CD: 201, and IBDU: 18), the incidence rates per 100,000 person-years were: IBD: 23.4 (95% confidence interval, 21.5-25.4), UC: 14.0 (12.6-15.6), CD: 8.6 (7.4-9.8), and IBDU: 0.8 (0.5-1.3). The median diagnostic delay was significantly shorter for UC (2.5 months (interquartile range [IQR] 1-6)) than for CD (5 months (IQR 1.5-11), p<0.01). Moderate-to-severe disability was reported by 34% of CD patients and 22% of UC patients (p=0.01), severe fatigue by 30% and 26% (p=0.43), and severely impaired health-related quality of life (HRQoL) by 43% and 30% of patients, respectively (p=0.01). Hospitalization rates (UC: 20%, CD: 34%, p<0.01), and need for immunomodulators, biologics, or surgery within three months of diagnosis, were high in both UC (3%, 7%, and 37%, respectively) and CD (31%, 18%, and 10%, respectively).

Conclusions: We found a high incidence of IBD in Copenhagen with a substantial disease burden characterized by early and high requirement for advanced therapies and high rates of fatigue, disability and impaired HRQoL at diagnosis.