Epidemiologic study of the irritable bowel syndrome in Beijing: stratified randomized study by cluster sampling.

To explore the prevalence of irritable bowel syndrome (IBS) in Beijing and its risk factors.Phase I: a screening for IBS in Beijing area according to symptoms using both Manning (modified including constipation) and Rome criteria. 2486 subjects were studied by cluster sampling of the inhabitant groups according to a stratified design of urban, suburban and rural areas, and sample size of each area studied was in proportion to the population of the area. Selection of the inhabitant groups was made by simple random sampling. Age of subjects enrolled in the study was 18-70 years. All subjects fulfilling the selection criteria were requested to fill in a questionnaire assisted by trained doctors or medical students during the visit to their families. Phase II: an aliquot of patients who fulfilled at least the Manning criteria were further selected according to their scoring series to undergo detail clinical examination in the hospital including laboratory examination, abdominal ultrasonography, colonoscopy or/and barium enema to exclude organic disease of the colon. Prevalence of IBS of the population was then adjusted by the rate of correct diagnosis during Phase II study. Study using Minnesota Multi-Personality Indices (MMPI) was done in some cases. Probable risk factors were explored by comparing their frequencies among IBS group and non-IBS group using chi 2 and logistic analysis of multifactors.The adjusted point prevalence of IBS in Beijing is 7.26% according to Manning criteria, and is 0.82% according to Rome criteria. There is a higher prevalence rate in city (10.50%) than in rural areas (6.14%) by stratified analysis (P < 0.001). Male to female ratio is 1:1.15. And IBS is more common in people aged between 18-40 years (51.6%), and among the intellectuals. Our study indicated that history of dysentery (OR 3.00), exposure to cool (OR 1.55) and ingestion of cold food and raw materials (OR 1.24) may be the most important risk factors (P < 0.001), and IBS patients may have a higher tendency of psychological abnormalities.IBS is a common disorder in Beijing and should be taken into consideration in the human welfare strategy.