Commentary: Understand the evolution of IBD
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In this Commentary, Gilaad G. Kaplan, MD, of the department of medicine, University of Calgary, Alberta, Canada, discusses the four epidemiological stages of inflammatory bowel disease (IBD) and reviews the forecast of disease prevalence and how disease penetration through a population evolves over time.
There are four epidemiological stages of IBD — emergence, acceleration in incidence, compounding prevalence and prevalence equilibrium. We believe we could place every country into one of the first three epidemiological stages of IBD evolution, currently. Over time, we feel that countries will transition through all of the first three stages, and eventually we will see entry into the prevalence equilibrium stage that, at this point in 2020, we don't believe has happened yet.
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It starts with the first stage, emergence, and the idea that IBD is a modern disease. For example, ulcerative colitis only entered the medical vernacular in 1888. Then, in 1932, Crohn, Ginsberg and Oppenheimer identified what we now call Crohn's disease. Although the first documented case of IBD — as we now know it — is arguably Matthew Baillie’s 1793 Morbid Anatomy publication, it is during this period that IBD makes its emergence in the Western world.
The next stage is acceleration in incidence, characterized by a rapid rise in incidence, but low prevalence. The transition between the acceleration in incidence and compounding prevalence stages is when incidence stabilizes, or even declines, but prevalence continues to grow exponentially: We found incidence in many regions of the Western world was stabilizing and, in some places, declining at the 21st century.
In the compounding prevalence stage, although incidence rates remain relatively stable, the total prevalent population in a region continues to rapidly grow; this is because IBD is predominantly a disease of young people, though it can be diagnosed at any age. People diagnosed with IBD will have it the rest of their lives because there is no cure. However, the likelihood of dying of IBD is actually very low. The stable addition of new cases outpaces the rate of mortality and, thus, the total prevalent population continues to grow rapidly.
In the prevalence equilibrium stage, prevalence finally stabilizes. We don’t think any country in the world is currently in this stage. Stabilization of prevalence is the result of an aging population with increased mortality from age-related comorbidities — along with age-targeting diseases like COVID-19. Due to age-related complications from long-term disease and the increased likelihood of comorbid conditions, we're going to have to adapt clinics to be able to handle that population.
Management over time
Regarding management, it really relates to two conceptual ideas. One is available management in the moment in time that you're looking at, the other is management in 2020 and beyond, which is what we’re more interested in so that we can start to prepare health systems for increased demand. For example, in Canada, we forecast prevalence increasing by 3% per year and that we will reach 1% of the population by 2030. It's not just the number of people with IBD necessitating changes to health care delivery, it's also the fact that a population is aging. Management of IBD changed over the last two decades, because the needs of the IBD community have changed: These changes include advances in surveillance and treatment, telemedicine interactions during the COVID-19 pandemic, and expanded health care teams to manage complicated disease due to comorbid conditions.
Importance of looking at evolution
We're seeing that in countries throughout Asia, Latin America and Africa, year after year, the incidence is rising. Prevalence in these countries still remains low, and the number of people who have IBD in their clinics still remains low, placing most of these regions in one of the first two stages of IBD evolution. The age of the IBD population is still skewed to a much younger age, compared with the average IBD clinic in Canada and the United States, for example.
There's two major concepts driving the rise in incidence prior to stage 3. One is the unmasking of incidence: We see this in a number of newly industrialized and developing countries; as they become economically more advanced in their health care infrastructure, they become better able to accurately diagnose the diseases. The other concept is a true rise in incidence: More people are being diagnosed with IBD today than were in previous decades, and that's really driven by the Westernization of society. We're mapping the global evolution of IBD to understand at what point each country might transition to the next stage, and the health care infrastructure needed at that stage. Therefore, thinking about these epidemiological stages and what will happen in the future is really important because as much as our history with IBD in Western nations can be approximated by developing and newly-industrialized countries, those countries’ future with IBD can be predicted by our past and present experiences.
Next step in research
If we can slow down incidence, meaning prevalence will not climb as fast, we can focus on studies that explore the underlying determinants that drive incidence. Then we can gain insight into how to mitigate disease and curb the incidence of IBD even further. There are a lot of uncertain circumstances such as the impact of COVID-19 on IBD. One of the things that we're exploring right now is how COVID-19 will impact models going forward considering that it's going to have an unequal impact on mortality, relative to age, but we also recognize that COVID-19 will have a bigger impact on some countries than others.
Beyond Canada, other countries (eg, Scotland) have forecasted that the IBD population will make up 1% of their population by 2030. We think most of the Western world is going to be somewhere in that 1% region in roughly the next decade, prior to a transition to stage 4. The categorization of a given countries’ current stage of IBD evolution allows us to predict the future burden of disease in that region and inform policy-makers for early intervention to prepare their local health care systems.
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