Incidence of Inflammatory Bowel Disease in New Zealand Remains High, Findings in the Manawatu Region.

ABSTRACT

BACKGROUND: New Zealand (NZ) has one of the world's highest rates of inflammatory bowel diseases (IBD), however available data are limited to southern, urban regions. AIMS: To determine the incidence and prevalence of IBD in the Manawatu region of NZ. METHODS: Patients in the Manawatu region, with a diagnosis of IBD made between 2011 and 2015 were identified. Demographic, diagnostic and disease data were collected, fulfilment of diagnostic criteria was assessed, and incidence rates were calculated. Comparison of disease phenotype and observed diagnostic criteria was made between diagnosis and 12-months following diagnosis. All resident patients with a diagnosis of IBD current on 5 March 2013 were identified, and prevalence rates were calculated. RESULTS: The mean annual age-standardised incidence rates of UC, CD, and IBD were 10.2, 17.0, and 27.2 per 100,000. IBD incidence was highest among those of European ethnicity (24.8 per 100,000), followed by Asian (1.4), and Maori (1.1). IBD incidence in the urban population was 34.0 per 100,000 (95% CI 24.1-46.0) compared to the rural population of 5.6 (95% CI 0.4-22.4). The age-standardised point prevalence of UC, CD, and IBD on 5 March 2013 was 157.7, 231.8, and 397.9 per 100,000, respectively. CONCLUSIONS: The incidence and prevalence of IBD in the Manawatu region are comparable to those reported in other Australasian studies. Incidence was lower in Maori, and in the rural population. Follow-up is required to identify any changes in incidence and phenotype, and whether rural residence remains protective.