Abstract
Introduction: The epidemiology of inflammatory bowel disease (IBD) in New Zealand (NZ) has been explored in regional studies but not at a national level. This study aimed to use administrative data to define the first nationwide IBD population and estimate the incidence, prevalence and mortality of IBD in NZ.
Methods: The Integrated Data Infrastructure (IDI) is a statistical database linking population-level health data. An IBD population was created within the IDI using hospital discharge information by International Classification of Diseases, Tenth Revision code. Incidence and prevalence rates were calculated for 16 years (2006/07-2021/22) by age, sex, ethnicity and urban/rural location. Age-sex-standardised mortality was measured annually from 2012 to 2022.
Results: Between 1 July 2021 and June 30 2022, 19 566 people in the IDI were identified as having IBD, giving a prevalence of 391.4 (95% confidence interval (CI) 386.0-396.9) per 100 000 people. The prevalence of Crohn's disease (CD), 206.9 (95% CI 203.0-211.0), was similar to that of ulcerative colitis (UC), 213.2 (95% CI 209.2-217.2), both per 100 000 people. In the same year, 1407 new cases of IBD were observed, giving an incidence rate of 28.1 (95% CI 26.7-29.7) per 100 000 person-years. The 2012-2022 standardised mortality ratio for IBD was 1.69 (95% CI 1.60-1.79).
Conclusions: A high incidence and prevalence of IBD were seen in NZ, and increased all-cause mortality rates were observed. Despite the limitations of using hospital data, this work established the value of IDI data for IBD epidemiological studies and produced national estimates of IBD burden.