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P673 Annual Incidence of IBD in Otago, New Zealand: An 18-year Epidemiological Analysis

C. Galts1, F. Huinzing1, A. Gray2, J. Norton1, K. Copell1, M. Schultz*1

1University of Otago, Department of Medicine, Dunedin School of Medicine, Dunedin, New Zealand, 2University of Otago, Department of Preventive and Social Medicine, Dunedin School of Medicine, Dunedin, New Zealand


The incidence of Inflammatory Bowel Disease (IBD) continues to increase in some regions of the world, while in others it plateaus or even declines. It has been previously shown that New Zealand has one of the world's highest IBD incidence rates, but changes over time have not been investigated. The aims of this study were to determine the annual incidence of IBD, Crohn's Disease (CD) and Ulcerative Colitis (UC) in the Otago region, New Zealand from 1996 to 2013 and to examine changes in demographics and disease presentation at diagnosis over the 18-year study period.


All patients in Otago who had at least one ICD-10 code for IBD (K50.X and 555.X for CD, K51.X and 556.X for UC, and K52.3 and 558.9 for IBDU) during the period 1996-2013 were identified. A diagnosis of IBD according to accepted criteria, the date of diagnosis, demographic information, phenotypic data, according to the Montreal classification and treatment details were extracted from individual patients' electronic and paper records. Age standardised annual incidence rates of CD, UC, and IBD-Unclassified (IBDU) were calculated and trends over time assessed. This study was approved by the University of Otago Human Ethics Committee.


442 Otago residents had confirmed IBD diagnosed during 1996-2013, of which 52% had CD, 40% UC and 8% IBDU. The median age at diagnosis for IBD was 35 (CD 31; UC 41) and the vast majority (97.1%) of new diagnoses were in patients with European ancestry, with a disproportionately low amount of cases in indigenous populations (IBD Maori 1.8% of all cases; Pacific Islanders 0.2% of all cases). The overall incidence over this time period for IBD was 13.4/100,000 (UC 4.46/100,000; CD 6.59/100,000) and the average annual age-adjusted IBD incidence rate increased by 0.27 cases per 100,000 people per year (p=0.095). The lowest incidence was recorded in 2006 for IBD with 6.4/100,000 people (CD 1.7/100,000; UC 2.6/100,000) and the peak incidence for IBD was 23.8/100,000 people in 2012 (CD 15.3/100,000; UC 5.7/100,000). Besides disease location in CD (increase in ileocolonic disease presentation L3, p=0.02), there were no significant changes in disease presentation over the 18 years (all p ≥0.19).


This study highlights the significant annual fluctuation of disease incidence and over the past 18 years there has been a slight but non-significant increase in IBD incidence. The average annual incidence for IBD remains one of the highest in the world. While the proportion of ileocolonic CD has increased, all other phenotypic measures for CD and UC have remained the same over the past two decades. In a nation with mixed ethnicities, IBD is more prevalent in those of European descent.