The four epidemiological stages in the global evolution of inflammatory bowel disease

Abstract

Inflammatory bowel disease (IBD) is a global disease; its evolution can be stratified into four epidemiological stages: Emergence, Acceleration in Incidence, Compounding Prevalence and Prevalence Equilibrium. In 2020, developing countries are in the Emergence stage, newly industrialized countries are in the Acceleration in Incidence stage, and Western regions are in the Compounding Prevalence stage. Western regions will eventually transition to the Prevalence Equilibrium stage, in which the accelerating prevalence levels off as the IBD population ages and possibly as a result of an unexpected rise in mortality during the COVID-19 pandemic. Mitigating the global burden of IBD will require concerted efforts in disease prevention and health-care delivery innovations that respond to changing demographics of the global IBD population. In this Perspective, we summarize the global epidemiology of IBD and use these data to stratify disease evolution into four epidemiological stages.

Fig. 1. Four epidemiological stages of IBD evolution.

The changing pattern in the incidence (orange) and prevalence (blue) of inflammatory bowel disease (IBD) across the four the stages of IBD evolution. Developing countries are in the Emergence stage, during which sporadic cases of IBD are documented. Newly industrialized countries are in the Acceleration in Incidence stage, during which incidence rises and prevalence is relatively low. Countries of the Western world are in the stage of Compounding Prevalence, during which incidence is stable, but prevalence is rising steeply. The slope of the prevalence increase will level off with the transition to the Prevalence Equilibrium stage, which represents the opposing force between an ageing IBD population and the incidence of IBD.

Fig. 2. Coalescing Incidence Ranges for IBD in regions in the Western world.

The Coalescing Incidence Range is the range of average reported incidence values as defined by the range between the 25th and 75th percentiles (interquartile range) of the amalgamated incidence data reported in a region. The boxes show the interquartile ranges of incidence rates reported for Western regions (data drawn from the 2017 systematic review by Ng et al.) for Crohn’s disease, ulcerative colitis and all inflammatory bowel diseases (IBD).

Fig. 3. The interplay and determinants of IBD incidence, prevalence and mortality.

The figure shows the Unmasking of Incidence by economic factors that improve the detection of undiagnosed inflammatory bowel disease (IBD) (for example, access to colonoscopy) and the True Rise in incidence due to westernization of society (for example, smoking) that influence the extent of incidence (water from the tap), which adds to the prevalent population (accumulation of water in the sink). The prevalence level is then affected by the rate of mortality, which is influenced by ageing of the IBD population with complications from longstanding disease, age-related comorbidities and COVID-19.

Fig. 4. Global map of the epidemiological stages of IBD evolution in 2020.

Regions are organized into anticipated current epidemiological stage of inflammatory bowel disease (IBD) evolution according to United Nations development classifications (2020). Regions in the first stage (Emergence) are highlighted in green, regions in the second stage (Acceleration in Incidence) are highlighted in yellow and regions in the third stage (Compounding Prevalence) are highlighted in orange. Regions with black borders are regions for which population-based incidence or prevalence studies are available. Regions with grey borders lack data on incidence or prevalence, highlighting current gaps in knowledge of IBD epidemiology^,.