Research in context
Evidence before this study
In a previous systematic review, we searched MEDLINE from 1950 to 2010 (8103 citations) and Embase from 1980 to 2010 (4975 citations) for population-based studies that reported the incidence or prevalence of Crohn's disease or ulcerative colitis. The search identified 260 population-based studies on the incidence or prevalence of Crohn's disease or ulcerative colitis. Collectively, these studies defined the epidemiological patterns of the inflammatory bowel diseases during the 20th century. Since the 1950s, the incidence and prevalence of inflammatory bowel disease steadily increased in the countries of North America, Europe, and Australia. During this time, more than two-thirds of studies reported that incidence rates were increasing significantly in the western world. We define the western world as consisting of countries influenced by a western European cultural heritage, including the USA, Canada, Australia, New Zealand, and all countries in western Europe. By contrast, few population-based studies on the epidemiology of inflammatory bowel disease were published from countries in Africa, Asia, and South America. At the turn of the 21st century, additional epidemiological studies have been reported from across the world. For example, the Asia-Pacific Crohn's and Colitis Epidemiologic Study Group (ACCESS) defined the incidence of inflammatory bowel disease in 12 countries in Asia and Australia. These newer studies, which were not included in the original systematic review, have shed light on the changing global epidemiological patterns of inflammatory bowel disease.
Added value of this study
We did a systematic review of population-based studies on the incidence (119 studies) or prevalence (69 studies) of inflammatory bowel disease from 1990 to 2016. Since 1990, incidence rates have shifted in western countries, with 73% of studies on Crohn's disease and 83% of studies on ulcerative colitis showing stable or falling incidence. However, disease burden remains high, with prevalence surpassing 0·3% in North America, Oceania, and most countries in Europe. By contrast, newly industrialised countries in Africa, Asia, and South America whose societies become increasingly westernised and urbanised, are mirroring the progression of inflammatory bowel disease in the western world during the 1900s.
Implications of all the available evidence
Since the recognition of ulcerative colitis in 1875 and Crohn's disease in 1932, the incidence of inflammatory bowel disease has increased substantially in the western world. Our findings show a paradigm shift whereby the incidence of inflammatory bowel disease in most western countries has begun to stabilise and in some regions decrease. However, after several decades of sharply rising incidence, the prevalence of inflammatory bowel disease has risen to more than 0·3% of the population in North America, Australia, and many countries in Europe. The high prevalence of inflammatory bowel disease in the western world will challenge clinicians and health policy makers to provide quality and cost-efficient care to patients with inflammatory bowel disease. More striking is the observation that as newly industrialised countries have transitioned towards a westernised society, inflammatory bowel disease emerges and its incidence rises rapidly. The peak in the incidence of inflammatory bowel disease has probably not yet transpired in these newly industrialised countries. Consequently, these countries will need to prepare their clinical infrastructure and personnel to manage this complex and costly disease. During the past 100 years, the incidence of inflammatory bowel disease has risen, then plateaued in the western world, whereas countries outside the western world seem to be in the first stage of this sequence. Thus, future research should focus on identification of the environmental risk factors seen during the early stages of industrialisation of society to highlight avenues to prevent the development of inflammatory bowel disease.