INTRODUCTION

Population-based studies of inflammatory bowel disease (IBD) in Cardiff have recorded data back to 1930 for Crohn's disease (CD) and 1968 for ulcerative colitis (UC). This study compares incidence and phenotype for 2005-2016 with past data.

METHODS

All new IBD cases resident in the Cardiff at diagnosis were collected retrospectively for the 12-year period 2005-2016, and compared with previous Cardiff data for trends in incidence and phenotype. Overall incidence was age/sex corrected to the UK population.

RESULTS

There were 991 new patients: 34% had CD, 5.4% IBD unclassified (IBD-U) and 60.5% had UC. The corrected incidence of CD was 7.7 per 100,000 person years [95% CI 6.9-8.6]. CD incidence is significantly higher than previous Cardiff studies, but the annual percentage change (APC) for 1980-2016 of 0.06; [95%CI -0.02 to 0.14] is not significant, with a previous higher APC for 1953-1980 of 0.18, [95%CI 0.13 to 0.23]. Uncorrected IBD-U incidence was 1.3 per 100,000 person years [95% CI 1.0-1.7]. UC corrected incidence was 14.4 per 100,000 person years [95% CI 13.3-15.6]. Incidence of UC is greater than in previous studies but did not increase during the current 12-year period. CD distribution at diagnosis continues to change as in previous Cardiff studies, with further increase in colonic disease and ileocolonic, (42% L2, 28% L3) and reduction in isolated terminal ileal disease (29% L1).

CONCLUSIONS

Incidence of both CD and UC are no longer rising significantly, but the location of CD at diagnosis continues to change with an increase in colonic location.Key messagesWhat is already known? It is unclear whether the incidence of IBD has now plateaued in urbanised nations. Changes in Crohn's disease location are often not reported in incidence studies and terminal ileal disease has usually been reported as the commonest site of diseaseWhat is new here? The incidence of UC and Crohn's is no longer rising in Cardiff UK, but the phenotype has changed progressively over time with a continuing increase in colonic disease location and decrease in isolated terminal ileal diseaseHow can this study help patient care? Understanding that Crohn's colitis is the predominant location has implications for diagnostic tests and implications for treatment optionsIMPACT STATEMENTThis work shows that although IBD incidence is no longer rising, the pattern of Crohn's disease is changing with more colonic disease and less isolated terminal ileal disease.PRACTITIONER RELEVANCE STATEMENTThe changing pattern of Crohn's disease location has implications for diagnostic assessment and treatment of this disease.