Does the incidence of IBD increase when persons move from a low- to a high-risk area?

Inflammatory bowel disease (IBD), both Crohn’s disease (CD) and ulcerative colitis (UC), are much more common in the countries of Europe and North America.1,2 Over the last several decades CD has been noted in these populations to have increased even further, whereas UC has remained much the same.3 In 1997 an article from the United Kingdom described IBD as essentially being confined to Western countries.4 In North America, Americans of North European descent have more than a 4-fold increased incidence than Americans of African-American descent.1 In this population, Jews of European descent have a 5-fold increase compared to that of Caucasians. Other North American studies have shown that the incidence in Caucasians is much greater than those of African-Americans, which is greater than Asians and those of Hispanic origin.2 In countries of low incidence, e.g., Seoul, Korea, there has been a 10-fold increase in UC since the 1980s.2 To answer the specific question, one needs to study populations in the developing countries, obtain accurate figures for the incidence and prevalence of both CD, and UC and then compare these when migration occurs of these populations to countries where the incidence and prevalence is much higher, that is, in Europe or North America. This migration underscores the impact and importance of environmental risk factors. There is increasing knowledge of the importance of the bacterial population, resident in the human gut, and its influences on IBD. There are now known to be important bacterial epithelial cell interactions that are thought to be involved in the pathogenesis of IBD. There are very few studies of the total population of bacteria in humans but there have been major breakthroughs in the ability to study these bacterial populations and they are now being applied to the IBD populations. As of yet, they have not been applied to countries where the prevalence is low and then restudied in the same people who migrate to countries where the prevalence is high. It will be this kind of crucial information that will pinpoint whether a move from developing to developed countries is accompanied by a corresponding change in colonic bacterial populations. Other possibilities could be the effect of infestations and parasites. The incidence of helminths is known to be high in developing countries and it is postulated that this is a potential factor in keeping the immune status of the individuals continually stimulated such that IBD does not develop.5 Benign eggs from worms have been used to treat CD with successful results in subjects residing in developed countries.6 Following along the same lines, it is postulated that the increasing incidence of CD (7/100,000) documented in India may be related to improved sanitation.7 CD is a disease of the twentieth century, described in 1932, with scattered reports of over the preceding 50 years. In India, UC was first reported in 1964 and CD was considered almost nonexistent until 1986.8 In the last 10 years CD has been reported more frequently from different parts of India. The main differential diagnosis in India is tuberculosis affecting the small and large bowel. There is now documented decrease of the incidence of tuberculosis and an increased incidence of CD. This has also been addressed by examination of the IBD incidence in people from Bangladesh who emigrated to East London, UK; here the incidence of IBD is rising and that of abdominal tuberculosis is falling in this subpopulation.9 Similarly, there are epidemiological studies of CD in Indian migrants moving to the county of Leicestershire in the UK, where the county population of 993,000 includes 10% South Asians, mostly from India.10 The standardized incidence in South Asians in the 1980s was 2.4/100,000 in Hindus, 3.4/ 100,000 in Sikh’s, and 5.4/100,000 per year in Muslims. There has been a rise in the standardized incidence of CD in Europeans to 4.7/100,000 from 3.4 in the 1970s. In Leicester this increase can be entirely explained by new cases of colonic disease. Similarly, epidemiology studies of IBD in the pediatric East Indian population of British Columbia document the incidence rates for CD to be 6.8/100,000 and 5.44/100,000 for UC between 1996 and 2001.11 In a 3-year prospective study among Europeans and firstand second-generation South Asians in Leicester from the years 1991–1994 documented that extensive UC was more common in the second-generation migrants than the first generation and was comparable to that in the European community.12 The annual average incidence of UC was 9.1/ 100,000, similar to a previous retrospective study. However, From the Division of Gastroenterology, Zeidler Ledcor Centre, University of Alberta, Alberta, Canada. Copyright © 2008 Crohn’s & Colitis Foundation of America, Inc. DOI 10.1002/ibd.20562 Published online in Wiley InterScience (www.interscience.wiley.com).