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Background: Crohn's disease (CD) and ulcerative colitis (UC) are considered rare diseases in developing countries. We have evaluated the incidence and prevalence of CD and UC over time in a district of Seoul, Korea.
Methods: A population-based study was performed from 1986 to 2005 in the Songpa-Kangdong district of Seoul. To recruit patients as completely as possible, multiple information sources, including all medical facilities in the study area and 3 referral centers nearby but outside the study area, were used.
Results: During the 20-year study period, 138 incident cases of CD (102 men, 36 women) and 341 incident cases of UC (170 men, 171 women) were identified. For the 20-year period, the adjusted mean annual incidence rates of CD and UC per 100,000 inhabitants were 0.53 (95% CI 0.44–0.62) and 1.51 (95% CI 1.34–1.67), respectively. When analyzed by 5-year intervals, the mean annual incidence rates of CD and UC increased significantly, from 0.05 and 0.34 per 100,000 inhabitants, respectively, in 1986–1990 to 1.34 and 3.08 per 100,000 inhabitants, respectively, in 2001–2005. The adjusted prevalence rates of CD and UC per 100,000 inhabitants on December 31, 2005, were 11.24 (95% CI 9.29–13.18) and 30.87 (95% CI 27.47–34.27), respectively.
Conclusions: The incidence and prevalence of CD and UC in Seoul, Korea, are still low compared with those in Western countries, but are rapidly increasing.
Crohn's disease (CD) and ulcerative colitis (UC), collectively termed inflammatory bowel disease (IBD), are heterogeneous chronic relapsing disorders of unknown etiology. Knowledge of the incidence rates of IBD in different geographic areas or among different ethnic groups may provide insights into possible etiologic factors. Similarly, temporal trends in the incidence rates in a given area can provide valuable clues about etiology.1
The incidence rates of IBD have been found to be higher in the northern part of the world than in the southern part and higher among white populations than among nonwhite populations.2 In general, the incidence of CD is strongly correlated with that of UC. Epidemiologic studies from Western countries have also shown that the increase in the incidence of UC precedes the increase in the incidence of CD by about 15 to 20 years.3–8 In some regions, the incidence of CD is now higher than that of UC.9–11
We previously reported that during the period from 1986 to 1997, the incidence rate of UC in Korea was still lower than that in Western countries but was increasing rapidly.12 However, the incidence and prevalence of CD have not yet been determined in Korea. We therefore evaluated the incidence rates of CD over a 20-year period, from 1986 to 2005, in the Songpa-Kangdong district of Seoul, Korea. We also updated our previous data about the incidence rates of UC in the same region and compared them with those of CD. In addition, the demographic and phenotypic features at the time of diagnosis of Korean patients with IBD were assessed and compared with those of Western countries.
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We have shown here that the incidence and prevalence of both CD and UC in Seoul, Korea, although still low compared with Western countries, are increasing rapidly over time. This rising incidence, which has not yet reached a plateau, suggests that some as-yet-unknown triggering environmental factors are involved in the development of both CD and UC in Korea. In addition, we found that the incidence ratio of UC to CD is decreasing in Korea, indicating that the incidence rate of CD may catch up with or even surpass that of UC in Korea, as it has in several Western countries.9–11 This temporal trend in incidence rates may provide valuable clues to the etiology of IBD, as well as useful information for the creation of health care policy in Asian countries in which reliable epidemiologic data on IBD are generally lacking.
To determine whether the progressive increase in UC and CD incidence is real, it is important to discuss the factors that can generate false trends of increasing incidence. Previous results have indicated that the increasing incidence of UC in Korea was not due to improved accessibility to medical facilities, change in diagnostic tools, inconsistent diagnostic criteria, or increased physician awareness of the disease.12 Although the results presented here, showing a trend toward an increase in the proportion of patients with ulcerative proctitis over time, may suggest that improved sensitivity for diagnosing mild UC may have contributed to the rising incidence, we also found that the absolute number of new patients with extensive colitis or left-sided colitis is also increasing. In addition, the interval between symptom onset and diagnosis was constant during the study period. Taken together, it is unlikely that the increased incidence of UC is a result of improved diagnostic sensitivity alone.
We found that the number of new patients with isolated colonic CD has remained constant, whereas the number with isolated small bowel disease, which is relatively difficult to diagnose, is increasing. Although this may suggest that the increased incidence of CD over time is a result of the availability of new diagnostic modalities such as capsule endoscopy or double-balloon enteroscopy, we found that only 6 patients underwent these procedures, none of whom was diagnosed with isolated small bowel disease by these procedures alone. In addition, we found that the number of new patients with both small bowel and colonic disease, the predominant type in our study, is increasing. Therefore, improved diagnostic sensitivity for small bowel lesions has contributed little to the overall increase in the incidence of CD in our study. Moreover, like UC, the time interval from symptom onset to CD diagnosis was constant during the study period, indicating that increased incidence was not caused by increased awareness.
One of the most interesting findings of our study is a marked male predominance in the incidence of CD in Korea. This finding contrasts with that of Western studies,9, 10, 17, 18 which have reported a slight female predominance of CD incidence in Western populations. Differential rates of smoking between men and women might cause the male predominance of CD. However, considering that the male-to-female ratio of UC was 1:1 in our study, it is unlikely that the smoking factor can explain the male predominance of CD in our study. Recently, several reports have shown a male predominance among newly diagnosed pediatric patients with CD in Western countries, suggesting a changing sex pattern from female to male predominance in this age group.19–23 However, our result is still different from these Western reports in that we could observe a male predominance of CD not only in pediatric but also in adult populations in Korea. A male predominance of CD has also been observed in Japan24 and Hong Kong.25 Taken together, these findings suggest that there may be sex-related differences in triggering or predisposing factors between Asian and Western populations.
Regarding the age distribution of incidence, it seemed that for both CD and UC, there was a second small peak in the 60–69 year age group, similar to findings in Western populations.3, 26–30 In contrast, studies in Asian populations31–33 have not reported this second peak. These studies, however, included too few patients for reliable age distribution curves, or they reported only the number of patients in each age group but not age-specific incidence rates.
The proportion of UC patients with proctitis at diagnosis has been regarded as a marker for the completeness of the patient collection.34 Our finding, that 43.7% of UC patients had ulcerative proctitis, is comparable to the 30% to 51% reported in Western population–based studies10, 17, 28–30, 35, 36 but is higher than that in Asian populations.31, 32, 37 These Asian studies, however, were hospital based and may not have included all patients with mild UC. In analyzing the location of CD, we did not separate patients with upper gastrointestinal disease by the Vienna classification,16 both because upper endoscopy was performed in only a small proportion of the patients and because in some patients, it was difficult to discriminate lesions limited to the terminal ileum from those proximal to the terminal ileum. We found that about two-thirds of CD patients had both small bowel and colonic disease, whereas only about 10% had isolated colonic disease. These findings are in contrast with those of most recent European studies, which reported that isolated colonic disease was the most common type of CD.26, 27, 35, 38 However, our results are comparable with those in Japan,39 suggesting that the location of CD in East Asian countries may be different from that in Western countries.
A positive family history has been shown to be the strongest risk factor for the development of IBD.40, 41 However, the degree of familial aggregation of IBD may differ by geographic area and/or ethnic group. We found that only 2.7% of our IBD patients had a family history of IBD, much lower than the 5% to 18% of patients in Western countries.42–47 However, the frequency reported here was about 2-fold higher than the 1.3% reported previously in this same district.48 When coupled with the 2-fold increase in IBD prevalence over the same time period, from 19.81/100,000 to 42.11/100,000, it is likely that the increase in frequency of family history simply reflects the increase in IBD prevalence in this area. That is, the low frequency of family history of IBD in Korea may result from the low prevalence of IBD in this country. Because the population relative risk of first-degree relatives of IBD patients in Korea was similar to that in Western countries,49 our findings suggest that the frequency of a family history of IBD in Korea will approach that of Western countries as the prevalence of IBD in Korea approaches that of Western countries.
In conclusion, we found that, although the incidence and prevalence rates of both CD and UC in our study area are lower than those of Western countries, they are increasing rapidly. These findings, together with the distinct demographic and phenotypic characteristics of Korean IBD patients, may provide clues to the etiology of these diseases, as well as useful information for health care policy.