Geographic distribution of inflammatory bowel disease in the UK: A spatially explicit survey

Inflammatory bowel disease (IBD) is characterized by chronic inflammation in the gastrointestinal (GI) tract, with two main forms: Crohn's disease (CD) and ulcerative colitis (UC). While CD can affect any part of the digestive system, UC predominately affects the colon and rectum. The incidence and prevalence rates of IBD cases are increasing worldwide, including in Europe where the UK has one of the highest incidence and prevalence rates. This study reports on a new survey of IBD cases in the UK, involving 5,452 respondents. The survey was promoted periodically by multiple IBD organizations across the UK over 307 days (01 Dec 2021-03 Oct 2022) and collected data on participants' IBD diagnoses and histories. The distributions of CD and UC cases were examined on a grid scale and based on these distributions, relative risk was calculated and mapped in regions where CD and UC cases were recorded. In addition, age- and sex-standardized morbidity rates (ASMRs) for CD and UC were calculated. The results of this UK-wide IBD study reveal an even geographical distribution of reported IBD cases and relative risk across the UK. The ASMR analysis revealed that the reported morbidity rate for women (in the 20-59 age range) was much higher than the morbidity rate for men in both CD and UC cases. In addition, the CD:UC ratio, which has the advantage of normalizing for possible sampling biases, revealed a cluster of large values (i.e., relative risk of CD) in the North-West England which may require further investigation.