Epidemiology of inflammatory bowel disease
Introduction
Crohn's disease and ulcerative colitis are chronic inflammatory diseases of the gastrointestinal tract, primarily affecting the small intestine and colon. Although many current hypotheses implicate a combination of environmental, genetic, and immunoregulatory factors, the cause of these two major subtypes of inflammatory bowel disease (IBD) remains unclear. Crohn's disease and ulcerative colitis are not common conditions and generally are not associated with increased mortality; however, they are associated with increased morbidity and decreased quality of life, are chronic conditions with a risk of relapse, and appear to be increasing in frequency in many areas of the world.
Epidemiology is defined broadly as the study of occurrence of illness. Descriptive epidemiology is the study of disease incidence; prevalence; temporal trends; and demographic factors such as age, gender, and ethnicity. Better understanding of the descriptive epidemiology of IBD (e.g., differences in prevalence of IBD based on age or geographic region) may identify areas for further research. This article reviews the descriptive epidemiology of ulcerative colitis and Crohn's disease.
Section snippets
Challenges in epidemiologic studies of inflammatory bowel disease
Epidemiologic studies of Crohn's disease and ulcerative colitis are fraught with difficulty. The diagnosis of IBD is not straightforward. The symptoms of IBD may be insidious in onset. Multiple investigations sometimes are required to make a firm diagnosis, and many other causes need to be excluded.
Comparing epidemiologic studies of IBD may be challenging. Diagnostic criteria for case identification in incidence and prevalence studies have varied considerably. Useful diagnostic tests such as
Incidence, prevalence, and temporal trends
Historically the highest incidence rates and prevalence for ulcerative colitis and Crohn's disease have been reported from centers in Scandinavia, the United Kingdom, and the United States [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [16], [17], [22], [27], [30], [31], [34], [36], [39], [43], [44], [45], [46], [47], [48], [49], [51], [52], [53], [56], [57], [58], [61], [62], [63], [64], [65], [66], [70], [75], [76], [77], [79], [80], [86], [88], [89], [90], [92], [94], [95], [96]
Gender distribution
In most studies of Crohn's disease, there is a slight female predominance, generally in the 50% to 60% range. A male predominance of Crohn's disease exists in many regions with low incidence rates [23], [82], [132], whereas a female predominance is much more common in moderate-to-high incidence areas. An extreme example of the latter can be found in Cardiff, Wales, where among new cases during the period 1991–1995, women outnumbered men by a greater than 2:1 margin [173]. The female
Age of onset
Although Crohn's disease is diagnosed most frequently in patients in their 20s and ulcerative colitis in patients in their 30s, the diagnosis can be made at any age. Approximately 10% to 15% of cases are diagnosed before adulthood.
The bimodal distribution of age at diagnosis of IBD typically refers to a peak in incidence in the second or third decade of life followed by a second (usually smaller) peak later in life, typically the sixth or seventh decade. Although commonly thought to be the
Ethnic and racial differences
Historically, IBD was thought to occur much less frequently in minority groups compared with whites and more frequently in persons of Jewish ancestry. Crohn's disease previously was thought to be so unusual among African-Americans that small case series were reportable [93], [119]. Studies in the 1980s and 1990s suggested, however, that the distribution of IBD among ethnic and racial groups continues to be dynamic.
The difference in IBD incidence and prevalence among whites and African-Americans
Summary
The incidence of IBD has either continued to increase or has stabilized at a high rate in most developed countries, whereas the incidence continues to rise in regions where IBD had been less common. The prevalence has continued to increase as a result of a combination of previously rising incidence and improved survival. Regardless of the exact prevalence, the burden of disease in North America and Europe is significant. Studying the patterns of geographic variation and age and gender
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