Increasing Incidence and Prevalence of the Inflammatory Bowel Diseases With Time, Based on Systematic Review

Natalie A. Molodecky; Ing Shian Soon; Doreen M. Rabi; William A. Ghali; Mollie Ferris; Greg Chernoff; Eric I. Benchimol; Remo Panaccione; Subrata Ghosh; Herman W. Barkema; Gilaad G. Kaplan

Disclosures

Gastroenterology. 2012;142(1):46-54. 

In This Article

Discussion

We present a comprehensive review of the worldwide incidence and prevalence of IBD. This review will help researchers estimate the global public health burden of IBD and the allocation of appropriate health care resources and research in specific geographic regions. Furthermore, by collating more than 200 reports on the incidence and/or prevalence of IBD, we anticipate that this report will serve as an essential resource for gastroenterologists and epidemiologists. Considerable differences were observed in the incidence of IBD across different geographic regions and over time. The majority of studies were conducted in European countries, whereas population-based data on the incidence and prevalence of IBD in developing countries were lacking. The highest prevalence of IBD worldwide was reported in Canada and Europe, whereas Asia had a lower prevalence of IBD. Studies that explored temporal trends showed that the incidence of IBD continues to increase in many regions of the world. Consequently, IBD appears to be emerging as a global disease.

The incidence and prevalence of IBD were highest in westernized nations, with the highest reported incidence rates in Canada (19.2 per 100,000 for UC[13] and 20.2 per 100,000 for CD[13,14]), Northern Europe (UC was 24.3 per 100,000 in Iceland[15] and 10.6 per 100,000 for CD in the United Kingdom[16]), and Australia (17.4 per 100,000 for UC and 29.3 per 100,000 for CD[17]). Similarly, prevalence was highest in Europe (505 per 100,000 for UC in Norway[18] and 322 per 100,000 for CD in Italy[19]) and Canada (248 per 100,000 for UC and 319 per 100,000 for CD[20]). Based on these estimates, approximately 0.6% of the population of Canada has IBD.[21] A North-South gradient has long been reported for IBD;[9] however, since the 1980s, this geographic distinction has been less prominent, with some of the highest incidence rates of IBD occurring in Southern Australia and New Zealand.[17,22] Sex differences were inconsistent, suggesting that the disease occurred equally among both sexes. Universally, incidence rates for both CD and UC were highest among the second to the fourth decade of life. Thus, IBD affects individuals in the most formidable and productive years of life, resulting in long-term cost to the patient, health care system, and society.[23]

The few studies that evaluated race/ethnicity reported the greatest incidence of IBD among white and Jewish people. However, the incidence of IBD in Hispanic and Asian people has been shown to be increasing,[24] and studies have shown that individuals emigrating from low prevalent regions (eg, Asia) to higher prevalent countries (eg, England) are at increased risk for developing IBD, particularly among first-generation children.[25] A lack of population-based studies evaluating race/ethnicity in developed nations and the paucity of data from developing countries highlight an important gap in the literature to be addressed in future studies.

In developing nations, IBD was a rare occurrence; however, as these nations have become more industrialized, the incidence of IBD has increased.[6,7] The emergence of IBD in traditionally low prevalent regions (eg, Asia) suggests that the development of IBD may be influenced by environmental risk factors. The geographic distribution of IBD provides clues for researchers to investigate possible environmental determinants of IBD. For example, IBD occurs more commonly in urban versus rural regions.[26–29] Individuals raised in urban areas of industrialized nations are exposed to considerably different environmental risk factors than those living outside these regions. Industrialization and urbanization of societies are associated with changes to microbial exposures, sanitation, occupations, diet, lifestyle behaviors, medications, and pollution exposures, which have all been implicated as potential environmental risk factors for IBD.[30] However, the exact relationship between genetic susceptibility and the role of the environment in the pathogenesis of IBD still largely remains a mystery. To advance our understanding of the key determinants of IBD in the developed and developing world, future population-based studies should focus on reporting incidence and/or prevalence of IBD stratified by gene-environment-phenotype interactions.

A statistically significant increase in the incidence of IBD was shown in 75% of CD and 60% of UC studies. Since 1980, 56% of CD and 29% of UC studies have shown a statistically significant increasing incidence. A significant decrease in the incidence of UC was only reported in 6.0% of studies, and none for CD. Thus, the incidence of IBD is increasing or stable in virtually every region of the world that has been studied. Because mortality in IBD is low[31] and the disease is most often diagnosed in the young,[32] these findings suggest that the global prevalence of IBD will continue to increase substantially. The rising incidence of IBD during the 20th century may be explained by environmental exposures that result from increasing urbanization; however, this increase could be due to increased awareness of IBD by physicians and the public, as well as advancements in diagnostic methods for IBD. Greater access to medical services, such as colonoscopies, in the latter part of the 20th century may have contributed to the increase in incidence of IBD. For example, the incidence and prevalence of ulcerative colitis in Punjab, North India, was only determined by conducting a house survey and performing sigmoidoscopy/colonoscopy among suspected cases.[33] Additionally, increased utilization of colonoscopy in developing countries may have led to greater differentiation of CD from UC, leading to relatively more diagnoses of CD. Future studies should adjust incidence rates by diagnostic procedure (eg, colonoscopy) utilization.

We conducted a comprehensive systematic review of the published literature on the incidence of IBD, but we did not perform a meta-analysis due to considerable variability between studies. There are multiple sources of heterogeneity, some of which include differences in population characteristics, study methodologies, and access to medical services and advancement of diagnostic procedures between countries. As a result, incidence rates and prevalence values are likely underestimated in studies published early in the observation period and in developing countries. Study quality was not used as an exclusion criterion and therefore likely contributed to differences in incidence estimates in the same geographic region. For example, the diagnostic criteria for IBD were not uniform across geographic regions and time.[34,35] Case ascertainment was different between studies, with some studies identifying IBD cases through administrative databases while others used patient registries. Some studies reported crude incidence rates, while others reported age- and/or sex-adjusted incidence rates. Furthermore, in the developing world, defining incidence and prevalence is considerably more difficult because many countries lack health care systems that compile health outcomes into administrative databases. In many developing nations, care is centralized in hospitals; thus, hospitalization records may more accurately reflect prevalence of disease as compared with hospitalization records from the developed world, where outpatient management of IBD is more common.

Limitations of the systematic review also include the exclusion of unpublished manuscripts and abstracts from conference proceedings. Studies that only evaluated the incidence of pediatric-onset IBD were excluded because of a previous report.[11] Further, when the incidence rates were reported separately for male and female subjects, an average was calculated. Similarly, an overall estimate was calculated when incidence rates for different races were reported and when the estimates were provided over multiple years. In the assessment of time trends, many studies only reported figures without specifying the numeric incidence rates over time. The incidence rates were extrapolated from these figures.

Despite these limitations, this systematic review provides a comprehensive overview of the incidence and prevalence of IBD across time and geography. The burden of IBD varied by geography and appears to be increasing over time. Definitive reasons for the increasing incidence rates of IBD are largely unknown. Despite more than 200 publications in the literature, our systematic review highlights the need for incidence and prevalence data in many regions of the world, particularly from developing countries. Future studies in these regions are required to provide further insight into the geographic patterns and time trends of IBD and will provide important insights into the etiology of IBD.

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