The Incidence of Inflammatory Bowel Disease in Chicago Over an 18-Year Period

Abstract

Introduction: The prevalence of inflammatory bowel disease (IBD) is highest in North America and Europe, and the incidence has been increasing over time1.In North America,studies of epidemiology in IBD have been limited and there are no epidemiological studies in a large urban city such as Chicago. The aims of our study are to determine the incidence of IBD in Chicago, and to assess changes in the incidence over time. Methods: We identified patients 18 years or older who had been seen at the University of Chicago Medicine (UCM) from Jan 1, 2000 to Sept 20, 2017. We used a unique database, the Clinical Data Research Warehouse, which includes all patients who have had any prior encounter at UCM. The database was queried for patients without a prior diagnosis of IBD for at least 6 months, and who were subsequently diagnosed with IBD at 2 separate encounters. Incidence was calculated by the number of new IBD cases, divided by the total number of cases in the study period, multiplied by 100,000 person-yrs. Medians were used to characterize age and time to diagnosis. Results: 1055 incident cases of IBD (548 CD, 507 UC) were identified. 578 were women, 388 black, 565 white, and 24 Asian/Pacific Islander. The median age at diagnosis was 37 (IQR 26-55). The median lag time from first encounter at UCM to diagnosis was 26 months (IQR 11-62). The median lag time was longer for black patients (46 months, IQR 18-88) in comparison to white patients (17months, IQR 9-44). The overall crude incidence rate of IBD was 117/100,000 person yrs. The highest incidence was in the 20-29 and the 30-39 age groups (27.8/100,000 and 22.1/100,000 person-yrs). The incidence rate for females and men was 64/100,000 and 53/100,000 person-yrs respectively. The incidence rate for blacks was 43/100,000 person-yrs, and whites was 63/100,000 person-yrs. From the period of Jan 1, 2000 to Dec 31, 2008 the incidence was 57.9/100,000 person yrs. Subsequently, from Jan 1, 2009 to Sept 20, 2017, the incidence was 59.3/100,000 person yrs. Conclusion: To our knowledge, this is the first study that looks at the incidence of IBD in a large, ethnically diverse, urban setting in North America. We found no change in the incidence of IBD over time. However, the lag time to diagnosis was longer in blacks than in whites. Further understanding of differences in clinical presentation and approach to diagnosis by providers is needed.