Inflammatory bowel disease (IBD) includes ulcerative colitis (UC) and Crohn's disease (CD), which are chronic inflammatory diseases of the gastrointestinal tract. The underlying aetiology and pathogenesis of IBD remains largely unknown, but are thought to result from an interaction between genetic susceptibility, environmental factors and the host immune response. IBD has been regarded as a disease primarily occurring in Western populations. High prevalence rates have been reported from North America, United Kingdom, and Northern Europe [1–3]. Although it was earlier considered rare in Asia [4–6], a number of recent reports suggest an increase in the incidence and the prevalence of IBD in the region [7–13]. Although better diagnostic awareness and increasing access to modern endoscopic technology may play a role, these factors alone are unlikely to explain this increase. Reasons for the increasing incidence of IBD in Asia are probably multi-factorial, and may at least partly be related to development and prosperity, resulting in improved hygiene and changing dietary habits [14]. Investigating the early stages of IBD as it emerges in new populations may provide a new opportunity to study its pathophysiology.

Unfortunately, data on the epidemiology and clinical characteristics of IBD in many Asian countries, and for that matter in most developing countries, are scarce [13]. Epidemiological and clinical information on IBD in many of these countries suffer from poor reporting networks, limited population based data, hospital data from undefined catchment areas, and non-uniform diagnostic criteria. There are also problems in diagnosis due to lack of awareness, poor resources, and problems of differentiating IBD from intestinal infections; circumstances where accurate incidence and prevalence figures are difficult to derive [14].

Sri Lanka is a country in economic transition, and disease patterns reflect this; there has been a gradual decline in diseases associated with poverty and an increase in non-communicable diseases. The epidemiology of IBD in Sri Lanka has not been investigated. We conducted a study to determine the prevalence and clinical characteristics of IBD in the Colombo and Gampaha districts of Sri Lanka. These two adjoining districts were selected as they appeared to be best suited for a hospital based survey: the two districts have a well defined catchment area for the regional hospitals; they are the most developed and populous in Sri Lanka; they have a reasonable ethnic and urban-rural mix, and high literacy rates (>95%) which would positively impact on health seeking behaviour [15].

There were 295 confirmed cases of IBD (UC = 240, CD = 55). Of these, 34 cases (UC = 30, CD = 4) were newly diagnosed during the study year. The prevalence of UC was 5.3/100,000 (95% CI 5.0-5.6/100,000) and CD was 1.2/100,000 (95% CI 1.0-1.4/100,000). The incidence of UC was 0.69/100,000 (95% CI 0.44 - 0.94/100,000) and CD was 0.09/100,000 (95% CI 0.002-0.18/100,000). Age related prevalence for UC and CD are given in Figure 2. Among 295 confirmed cases of IBD, the female:male ratios for UC and CD were 1.5 and 1.0 (Table 1). This trend for female preponderance in UC was observed in different age groups except in the 15 to 19 year group (Table 2). Of patients with UC, 89.7% were Sinhalese, 7.3% Tamil and 3% Muslim. 90.9% with CD were Sinhalese, 7.3% Tamil and 1.8% Muslim. The observed differences in type, extent and severity of disease generally reflected the districts' ethnic demography (Table 3). Mean age at diagnosis (males and females) for UC was 36.6 and 38.1 years, and for CD 33.4 and 36.2 years.

	Ulcerative colitis (UC) (N = 240)	Crohn's disease (CD) (N = 55)
Sex
Females	144	28
Males	96	27
Mean age at diagnosis
Females	38.1	33.4
Males	36.6	36.2
Ethnicity
Sinhalese	209 (89.7%)	50 (90.9%)
Tamil	17 (7.3%)	4 (7.3%)
Muslim	7 (3%)	1 (1.8%)
	-	-
Extent of disease (UC-221)
Distal	113 (51.1%)	-
Left-sided	50 (22.6%)	-
Extensive	58 (26.3)	-
Extent of disease (CD-55)
Only small intestinal involvement	-	7 (12.7%)
Only large intestinal involvement	-	44 (80%)
Large & small intestinal involvement	-	4 (7.3%)
Perianal disease	-	4 (7.3%)
Upper gastrointestinal involvement	-	3 (5.5%)
Severity of disease	(UC-166)	(CD-45)
Mild	97 (58.4%)	26 (57.7%)
Moderate	49 (29.5%)	10 (22.2%)
Severe	20 (12.2%)	9 (20%)
Extra-intestinal manifestations
Arthralgia and arthritis	68 (28.3%)	13 (23.6%)
Ocular disease	22 (9.2%)	9 (16.4%)
Skin rashes	18 (7.5%)	3 (5.5%)
Backache	17 (7.1%)	3 (5.5%)
Positive family history	5 (2.1%)	3 (5.5%)
Surgical intervention	11 (4.6%)	10 (18.2%)

Age group (years)	UC (F:M ratio/100,000)	CD (F:M ratio/100,000)
00-04	-	-
05-09	1.50	-
10-14	2.00	-
15-19	0.71	0.33
20-24	1.44	0.83
25-29	1.36	1.66
30-34	1.76	1.50
35-39	1.73	0.75
40-44	1.38	1.33
45-49	1.50	1.33
50-54	1.44	0.00
55-59	1.66	1.00
60-64	1.20	2.00
65-69	1.50	0.00
70-74	1.00	0.50
> 75	-	-

	Sinhala	Tamil	Muslims
General population of the two districts*	83.5%	8%	6.5%
UC	209 (89.7%)	17 (7.3%)	7 (3%)
Extent of UC
Distal	103 (91.2%)	7 (6.2%)	3 (2.6%)
Left sided	43 (86%)	4 (8%)	3 (6%)
Extensive	51 (88%)	6 (10%)	1 (2%)
Severity of UC
Mild	90 (92.8%)	4 (4.1%)	3 (3.1%)
Moderate	48 (98%)	-	1 (2%)
Severe	18 (90%)	2 (10%)	-
CD	50 (90.9%)	4 (7.3%)	1 (1.8%)
Extent of CD
Only small intestinal involvement	6 (85.7%)	1 (14.3%)	-
Only large intestinal involvement	41 (93.2%)	2 (4.5%)	1 (2.3%)
Large and small intestinal involvement	3 (75%)	1 (25%)	-
Perianal disease	3 (75%)	-	1 (25%)
Upper gastrointestinal involvement	3 (100%)	-	-
Severity of CD
Mild	23 (88.5%)	3 (11.5%)	-
Moderate	9 (90%)	1 (10%)	-
Severe	8 (88.9%)	-	1 (11.1%)

*Other ethnic groups 2%

At the time of diagnosis, among UC patients, 51.1% had proctitis, 22.6% left-sided disease and 26.3% extensive disease [173 out of the 240 (72.1%) UC patients had had a full colonoscopy to assess extent at the time of diagnosis), and 58.4% had mild disease, 29.5% had moderate disease, and 12.1% had severe disease. 80% of CD patients had only large bowel involvement. 2.2% of UC and 5.5% of CD patients had a positive family history. 40.4% of UC and 38.2% of CD patients had extra-intestinal manifestations. 4.7% of UC and 18.2% of CD patients had undergone surgery.

The present study, the first epidemiological study of IBD in this country, showed that prevalence rates were 5.3/100,000 for UC and 1.2/100,000 for CD. The incidence rates were 0.69/100,000 for UC and 0.09/100,000 for CD. The prevalence rates are low compared to Western populations [1–3], but are comparable to many, but not all, of the reported rates from Asia [14, 18, 19].

Shivanda et al. has suggested that a good epidemiological study for IBD should have a well-defined catchment area and up-to-date population data, good diagnostic facilities, uniform criteria of case definition, a common protocol and an established referral system [20]. Our study satisfied several of the above criteria. The two districts selected for the study have well defined catchment areas for the regional hospitals. Only permanent residents of the districts were included in the survey. As the most urbanised and developed districts in the country, demographic data are up-to-date, staffing and diagnostic facilities in hospitals among the best in the country. It is therefore unlikely that there is significant migration to other parts of the country for employment or health care. The high literacy rate of the population would also positively impact on health seeking behaviour [15]. Based on the results of the telephone interview of doctors in the smaller hospitals, it was reasonable to assume that most if not all IBD patients in the catchment area would be referred to specialists for investigation and treatment. The need to select only hospitals staffed by specialists would have improved the accuracy and uniformity of the diagnosis of IBD, especially because bowel infections are common in countries such as ours, and may trigger and alter the course of underlying IBD [21, 22]. However, there are limitations; being a hospital based study the survey was limited to symptomatic IBD patients seeking medical care, and direct data collection was limited to patients seeking health care in hospitals. Furthermore, patients who may have sought alternative forms of treatment would have been excluded. These limitations would have led to underestimation of the true incidence and prevalence of IBD in the districts.

We observed several differences in the clinical characteristics of IBD in our patients compared to Western patients. These may well be due to IBD in Asians being genetically and phenotypically different to IBD in Western populations. There was an overall female predominance for UC (F: M = 1.5:1) but no racial differences in prevalence. This is in contrast to reports from Western and most Asian countries where there is no sex difference. The mean age at diagnosis of our patients was slightly older than that observed in Western [3] and some other Asian studies [9–13]. This may be due to late presentation at the specialist hospital, but could also reflect milder disease in this cohort. IBD was uncommon among our children, unlike in Western series. Many Western studies have found a so-called 'second peak' of prevalence for UC in the over-65s. Our patient population showed peak prevalence in the fourth decade. The apparent bimodal age distribution (Figure 2) is in agreement with Western studies [23], but is difficult to draw firm conclusions on because of the relatively small number of UC patients and even smaller number of CD patients in our study. A family history for both UC and CD was uncommon, and may indicate a lesser genetic predisposition to the disease than in Western populations, but time trend studies of the prevalence of IBD are necessary to investigate this further. Most of our patients with UC had mild, distal or left sided disease clinically and endoscopically, and responded well to medical treatment, with only a few patients requiring surgical intervention. Many of our observations are similar to those in previous reports of UC from the Asian region [7, 24, 25].

The prevalence of UC and CD in this hospital based study was low compared to Western populations, but similar to some in Asia. Many features of IBD were similar to IBD in the West, but there were notable differences: there was a female preponderance for UC although there were no racial differences; IBD commonly presented in the fourth decade of life and was uncommon in children; only few of our patients had a family history; and most patients with UC had mild, distal or left sided disease. Investigating these differences as IBD emerges in developing countries may give further clues to its aetio-pathogenesis.

The authors wish to thank Professor KI Deen and Drs JVS Aryasinghe, KVU Kalubowila, S Kumaresena and CA Jayasuriya for help with the study.