Rising Incidence of Inflammatory Bowel Disease in Canterbury, New Zealand

Background: A population-based study of inflammatory bowel disease (IBD) in the Canterbury province of New Zealand demonstrated an incidence of Crohn's disease (CD) of 16.5 per 100,000 population in 2004, along with a high rate of IBD overall. At the time, this was one of the highest rates of CD in the world. The current study aimed to ascertain the incidence of IBD in the same area 10 years later. Methods: All patients diagnosed with IBD in 2014 within the Canterbury region were identified and characterized. Diagnosis and disease classification were ascertained using standard accepted criteria. Projected population data for age and gender were used to calculate incidence rates for IBD overall and for CD, ulcerative colitis (UC), and inflammatory bowel disease-unclassified (IBDU). Results: During the 2014 years, 205 patients were diagnosed with IBD in Canterbury. This group comprised 134 patients with CD, 69 with UC, and 2 with IBDU. The age-standardized incidence of IBD, CD, UC, and IBDU was 39.5, 26.4, 12.6, and 0.17 per 100,000, respectively. Disease location of CD patients was evenly distributed (ileal 29%, colonic 35%, and ileocolonic 32%). Similarly, patients with UC had even distribution of proctitis, left-sided, and extensive disease. Conclusions: This study demonstrates a substantial increase in the incidence of IBD in this geographically well-defined area. Overall, incidence rates were 1.6-fold greater than when assessed 10 years earlier. The reasons contributing to these continued increases remain unclear. However, further increases in rates of IBD indicate growing health system demands in the future.