Inflammatory bowel disease in Waikato, New Zealand: incidence and prevalence

Inflammatory bowel disease (IBD) prevalence is rising globally; however, indigenous groups are underrepresented. Waikato, New Zealand, is a large region with a high proportion of Māori patients. In Canterbury in 2006, 1% of patients with IBD were Māori. We investigated the incidence and prevalence of IBD in Waikato over 10 years.

This was a retrospective cohort study assessing the incidence and prevalence of IBD between 2009 and 2019. The search strategy included pathology, radiology, Provation, ICD-10 coding and private clinics, using the keywords: Crohn's, Crohn, ileitis, colitis, ulcerative, inflammatory bowel disease and IBD. Collected data included current age and age at diagnosis, sex, ethnicity and IBD subtype.

The IBD point prevalence on 31 December 2019 was 375.6/100 000 compared with 293.6/100 000 in 2010, increasing by 27.9%. The annualised incidence was static from 21.5/100 000 in 2010 to 17.5/100 000 in 2019. Female patients comprised 53.3% of the cohort. Ulcerative colitis (UC) made up 54.2% of cases, 43.8% had Crohn disease (CD) and 2.0% had indeterminate colitis. Sixty (3.7%) patients identified as Māori. In non-Māori patients, the average age at diagnosis was 36.2 years, compared with 33.0 years in Māori patients (P = 0.11). In Māori patients, 53.3% had UC and 45.0% had CD. Thirty-five percent of Māori patients lived 50 km or more from base hospital, compared with 41% of non-Māori patients (P = 0.33).

IBD prevalence has increased substantially; however, the incidence has remained static. Māori IBD rates are higher than previously reported, in keeping with international indigenous trends. Māori patients were diagnosed at a similar age as non-Māori patients, with similar disease subtypes.