1. Incidence
The most recent data on the incidence of IBD in Asian countries were shown in
Fig. 1. Recently, the incidence and prevalence of IBD in a population-based inception cohort from Songpa-Kangdong district, Korea was updated with a 30-year study period from 1986 to 2015 [
7]. The age- and sex-adjusted annual incidence of IBD has increased continuously throughout the 30-year period: from 0 in 1986 to 2.42/100,000 inhabitants in 2015 for CD and from 0.33/100,000 inhabitants in 1986 to 6.58/100,000 inhabitants in 2015 for UC. According to this study, CD incidence had increased approximately 40 times during the past three decades, and UC incidence had increased approximately 20 times. The average annual percentage change (APC) in IBD incidence was 12.3% during 1986-1995 and 12.3% during 1996-2005, whereas it was only 3.3% during 2006-2015 (
P< 0.05). This indicates a moderation in the increase in IBD incidence in recent years, despite the continued increase in the incidence of IBD. Recently, the incidence and prevalence data from Korea using a nationwide health insurance database reported conflicting results [
8-
10]. Two studies reported a plateau or even decrease in the IBD incidence in Korea between 2006 and 2014 [
8,
9]. One of the studies reported CD and UC incidences as 3.6/100,000 and 5.0/100,000, respectively, in 2006 and 3.1/100,000 and 4.2/100,000, respectively, in 2012 [
8]. The other study reported the incidences of CD and UC as 3.1/100,000 and 5.9/100,000, respectively, in 2011 and 2.4/100,000 and 5.0/100,000, respectively, in 2014 [
9]. However, the most recent study using this database reported of increased IBD incidence between 2009 and 2016 [
10]. This study reported the incidences of CD and UC as 2.4/100,000 and 4.0/100,000, respectively, in 2009 and 2.9/100,000 and 4.0/100,000, respectively, in 2016 [
10]. This discrepancy could be because of the difference in the definition of incident cases and relatively short washout periods between the enrollment in the administrative database and IBD diagnosis, which can cause a misclassification between the incident and prevalent cases [
11]. A similar discrepancy was observed for North America in which the incidence of IBD decreased between 1996 and 2009 in the Canadian population-based study [
12]. Cases may have been underestimated because IBD diagnosis was not based on clinical diagnosis and medical record review, but on a diagnostic code-based scoring systems including the International Classification of Diseases-9 codes, physician billing claims, and discharge diagnoses [
2,
11].
In 2019, longitudinal data on the incidence of IBD were reported in Taiwan [
13]. A retrospective analysis was performed using data, between January 2001 and December 2015, from the National Health Insurance and the Ministry of Health and Welfare, Taiwan. The crude incidence of CD increased from 0.17/100,000 in 2001 to 0.47/100,000 in 2015, and the crude incidence of UC increased from 0.54/100,000 in 2001 to 0.95/100,000 in 2015. The APC was 2.69 by the joinpoint trend analysis for the general trends in patients diagnosed with IBD, which was significant from 2001 to 2015. The trend of CD also increased significantly according to the joinpoint trend analysis from 2001 to 2015, with the APCs as 4.75 (2001-2010) and 15.92 (2010-2015), whereas they were nonsignificant in the trend for UC, given that the APC value was 0.82 from 2001 to 2015.
According to the multinational epidemiological study from Asia, the Asia-Pacific Crohn’s and Colitis Epidemiologic Study (ACCESS), the incidence of IBD had an increasing trend in Asian countries including Brunei, China, Hong Kong, India, Indonesia, Macau, Malaysia, Singapore, Sri Lanka, Taiwan, Thailand, and the Phillippines [
4,
14]. Between 2011 and 2013, the mean annual crude incidence of IBD per 100,000 in Asia was 1.50 (95% confidence interval [CI], 1.43-1.57). From 2011 to 2012, the crude overall annual incidence per 100,000 of IBD, CD, and UC in Asia was 1.14 (95% CI, 1.06-1.23), 0.35 (95% CI, 0.31-0.40), and 0.76 (95% CI, 0.69-0.84), respectively. From 2012 to 2013, and the corresponding incidence rates were 1.89 (95% CI, 1.77-2.01), 0.66 (95% CI, 0.60-0.73), and 1.20 (95% CI, 1.11-1.29), respectively.
In a multicenter study using a hospital and territory-wide administrative coding system from Hong Kong, the age-adjusted incidence of IBD per 100,000 individuals increased from 0.10 (95% CI, 0.06-0.16) in 1985 to 3.12 (95% CI, 2.88-3.38) in 2014 [
15]. The age-adjusted incidence per 100,000 increased from 0.01 (95% CI, 0.00-0.05) in 1985 to 1.46 (95% CI, 1.29-1.65) in 2014 for CD and from 0.09 (95% CI, 0.05-0.15) in 1985 to 1.51 (95% CI, 1.35-1.69) in 2014 for UC.
In Japan, recent data on the longitudinal analysis of IBD epidemiology have been lacking. However, we have observed a constant increase in the incidence of IBD over the past 60 years, as published in the previous reports. In 1955, the incidence of CD and UC was 0.002/100,000 and 0.03/100,000, respectively [
16]. In 1991, the incidence of CD and UC had risen to 0.51/100,000 and 1.95/100,000, respectively [
17]. From 1986 to 1998, the CD incidence has been estimated to be as high as 0.9/100,000 [
18]. A recent report using a survey conducted in 2014 reported the incidence of CD as 2.0/100,000 and the incidence of UC as 12.2/100,000 [
19].
In China, longitudinal data on the trend in the incidence of IBD is not available. In meta-analyses that summarized the epidemiologic data on a national level, the incidence of CD was estimated at 0.28/100,000 during 1950-2002 and this was slightly increased to 0.85/100,000 on extending the period to 1950-2007 in mainland China [
20,
21]. A population-based study from Wuhan reported the age-adjusted incidence of IBD, CD, and UC were 1.96, 0.51, and 1.45/100,000, respectively [
22]. According to ACCESS, the pooled incidence rates of IBD, CD, and UC in China were 1.61, 0.34, and 1.21, respectively, between 2011 and 2013 [
14]. In addition, within China, the pooled incidence of IBD varied from 0.18/100,000 to 0.73/100,000 for CD and 1.12/100,000 to 1.33/100,000 for UC according to the population density of the regions [
14].
In Southeast Asia and South Asia, only a few studies on the epidemiology or natural course of IBD have been published [
23-
27], most of which are referral-center-based studies. Based on the data from the ACCESS, the pooled incidence of UC was lower in Southeast Asia than that in East Asia (0.49/100,000 vs. 1.14/100,000;
P= 0.002) and the pooled incidence of CD was comparable between Southeast Asia and East Asia (0.36/100,000 vs. 0.34/100,000;
P= 0.878) [
14]. In Malaysia, the first population-based study from the Kinta Valley region reported the incidence of IBD as steadily increased over the past two decades; from 0.07/100,000 population-years in 1990-1995 to 0.69/100,000 population-years in 2005-2010 [
26]. In a Malaysian hospital-based study, the mean crude incidence of IBD had increased steadily between 1980 and 2018: 0.36 (1980-1989), 0.48 (1990-1999), and 0.63/100,000 person-years (2000-2009). From 2010 to 2018, the mean crude incidence doubled to 1.46/100,000 person-years [
28]. In the ACCESS, India showed a higher incidence of IBD than those of East Asia and Southeast Asia (9.31/100,000 vs. 1.53/100,000 and 0.80/100,000) [
14].