Prevalence and demographics of irritable bowel syndrome: results from a large web-based survey

Aliment Pharmacol Ther 2005; 22: 935 942. doi: 10.1111/j.1365-2036.2005.02671.x Prevalence and demographics of irritable bowel syndrome: results from a large web-based survey E. B. ANDREWS*, S. C. EATON*, K. A. HOLLIS*, J. S. HOPKINS*, V. AMEEN, L. R. HAMM*, S. F. COOK, P. TENNIS* & A. W. MANGEL* *RTI Health Solutions and GlaxoSmithKline, Research Triangle Park, NC, USA Accepted for publication 23 August 2005 SUMMARY Background: Irritable bowel syndrome is a common gastrointestinal disorder, and its prevalence and demographics have been evaluated by different methodologies with varying results. Aim: To evaluate irritable bowel syndrome demographic and prevalence characteristics utilizing a web-enabled panel. Methods: From an existing 150 000-member panel, 31 829 individuals were randomly selected and sent screening questionnaires to evaluate irritable bowel syndrome symptoms. Individuals who agreed to participate and completed the screening questionnaire received a second questionnaire related to a diagnosis of irritable bowel syndrome, a more detailed symptom description, and additional burden of illness data. Results: Irritable bowel syndrome prevalence was 7%. Prevalence was higher in women vs. men, unmarried individuals vs. married individuals and unemployed individuals vs. employed individuals. Of those completing the second questionnaire, 51% had seen their physicians for irritable bowel syndrome symptoms in the past year and most had an episode within the past 3 months. During the past year, approximately half of the participants had used a prescription medication, and over 90% had used an over-the-counter medication for irritable bowel syndrome. Participants with irritable bowel syndrome demonstrated quality-of-life reductions relative to norms of the United States population. Conclusions: Web-enabled data collection represents a novel tool for rapidly surveying a large population of individuals with irritable bowel syndrome symptoms. INTRODUCTION Irritable bowel syndrome (IBS) is the most common diagnosis made by gastroenterologists. 1, 2 Fundamentally, it is a diagnosis made only after appropriate exclusionary work-ups have ruled out an organic aetiology for the patient s symptoms. 3 However, the nature and completeness of the exclusionary evaluations are somewhat physician- and patient-dependent. It is recognized that the prevalence estimates for Correspondence to: Dr A. Mangel, RTI Health Solutions, 3040 Cornwallis Road, PO Box 12194, Research Triangle Park, NC 27709-2194, USA. E-mail: amangel@rti.org functional gastrointestinal disorders are very sensitive to the diagnostic definition used, as no pathognomonic laboratory, endoscopic, or radiographic findings exist. 2, 3 As the diagnostic criteria for IBS have evolved from the Manning Criteria 4 to Rome I Criteria 5 to Rome II Criteria, 6 varying IBS prevalences have been reported. 7 13 Measurement of the impact of IBS on patient s quality of life, determined by both the Medical Outcomes Study Short-Form 36 (SF-36) and several disease-specific instruments, shows a large negative impact associated with IBS. 14 20 The financial impact of IBS, based on direct medical costs, decreased work productivity, and increased work absenteeism, is also substantial. 21 24 An Ó 2005 Blackwell Publishing Ltd 935

936 E. B. ANDREWS et al. increased rate of pelvic and abdominal surgeries is also associated with IBS, further increasing the burden of illness of the disease. 25 Based on primary bowel symptom patterns, IBS is subtyped into diarrhoea-predominant, constipation-predominant, or alternating bowel habits (alternators). Although formal, widely-accepted, definitions do not exist for diarrhoea and constipation, bowel movement frequencies outside the range of three bowel movements per day to three bowel movements per week are often used to define the spectrum from diarrhoea to constipation. The ability of physicians to recognize states of diarrhoea and constipation has allowed for development of therapeutic agents specific to bowel subtype. 26 29 Data on demographic, healthcare utilization and burden of illness from clinic populations are not necessarily representative of the overall IBS population. The purpose of the present study was to evaluate the prevalence of IBS and characterize demographic characteristics of individuals with IBS symptoms in the general population. In addition, we characterize the social and health characteristics of individuals with symptoms of diarrhoea-predominant or alternating IBS. We report on the first use of a novel web-based panel for the identification and characterization of individuals with IBS. MATERIALS AND METHODS Subjects A sample was drawn from an existing online webenabled research panel. The panel consisted of over 150 000 household members, representative of the United States (US) population aged 21 65 years. 30 The survey was conducted between December 2001 and February 2002 and received approval by Research Triangle Institute s (RTI) Institutional Review Board (IRB). To avoid exclusion of non-users of computers or the Internet, all households participating in the panel were supplied with WebTV Internet service. Initially, a random sample of 31 829 men and women was drawn from the panel. Individuals who provided consent were sent a questionnaire (screening questionnaire, hereafter) for screening symptoms of IBS. Individuals who met screening criteria for diarrhoea-predominant IBS or alternative IBS were then sent a second questionnaire. The screening questionnaire asked: 1 Have you ever had continuous or repeated pain, cramping, or discomfort in your abdomen or bowels for at least 12 weeks (which need not be consecutive) in the past 12 months? and 2 In the past 12 months, which, if any, of the following have you experienced in combination with abdominal pain, cramping, or discomfort (select all that apply)? (a) Relief from abdominal pain, cramping, or discomfort with a bowel movement. (b) More frequent bowel movements. (c) Fewer bowel movements. (d) Loose or watery stools. (e) Firmer or harder stools. (f) None of the above. Participants were classified as responders if the answer to the first question was yes and at least one item was selected in the second question. Otherwise, they were non-responders. Diarrhoea-predominant subjects were defined as those who reported outcomes of (b) and/or (d), but not (c) or (e). Constipation-predominant subjects were defined as those who reported outcomes (c) and/or (e) but not (b) or (d). Alternators were defined as those who reported outcomes of (c) and/or (e) and (b) and/or (d). Those who selected outcome (f) were considered not classifiable. Information from the screening questionnaire was used to evaluate demographic characteristics and IBS prevalence. Questions 1 and 2 above are modified from the Rome II Criteria. As the Rome II Criteria are intended for use by physicians, and survey questions were presented to patients, language was modified for use by a lay population. The second questionnaire addressed symptoms, burden of illness, diagnosis and treatment of IBS during the 12 months prior to the survey. Participants were not asked about IBS symptoms per se, but rather, about abdominal symptoms. Participants completed questions regarding medical services; symptom history; medication use; IBS, irritable colon, or spastic colon diagnosis; surgery for abdominal symptoms; and time since last episode of recurring abdominal symptoms. SF-36. All participants completed the SF-36, a 36-item questionnaire that provides scores for eight domains of patient functioning: physical functioning, role physical, bodily pain, general health, vitality, social functioning, role emotional and mental health. 31 Each subscale was scored from 0 to 100, with higher scores indicating

IBS PREVALENCE FROM A WEB-BASED SURVEY 937 better health status. Scoring on the SF-36 is not linear, and interpretation of results is referenced to an extensive database of norms and comparative diseases. Missing data were imputed as per standard algorithms. Specifically, where there were missing item-level data, but more than half of the items in a given subscale were answered, the score was calculated by substituting the average item score for missing item values. If over half of the items in a particular subscale were missing, the score was treated as missing. Analysis. Continuous data were presented as mean ± standard deviation and categorical data were presented as proportions. Prevalences and 95% confidence intervals (CIs) were presented per 100 participants. Univariable analyses were conducted to compare the demographic profiles within IBS subtypes. For categorical data, group differences were tested using a Chi-square test, while for continuous variables, the two-sample independent t-test was used. SF-36 mean scores for SF-36 domains were compared between groups by the two sample independent t-test. A Bonferroni correction for the level of significance of alpha ¼ 0.05/8 ¼ 0.00625 was used as a correction for multiple domain scores between groups. Sample results on the SF-36 were compared with US population norms. All analyses were performed using SAS for Windows software (version 8.02; SAS Institute, Cary, NC, USA). RESULTS Subjects The screening questionnaire was sent to a randomly selected sample of 31 829 panel participants, and 25 986 (82%) participants completed the questionnaire. Characteristics of the sample population were, in general, reflective of the US population (Table 1). Those individuals who responded to the screening questionnaire were similar to the sample population (Table 1). The notable differences between the sample, participants and the general US population were that younger individuals (ages 21 29) were less likely to be in the sample, as were those with less formal education (Table 1). IBS participant demographics Of the 25 986 participants, 1713 met the criteria for IBS (IBS participants, hereafter). Of the IBS participants, Table 1. Comparison of the study population with the United States (US) population Demographic characteristics US population (%)* Sample (n ¼ 31 829) (%) Sex Male 48.8 48.8 48.8 Female 51.2 51.2 51.2 Age 21 29 20.1 14.7 12.8 30 44 39.4 41.4 40.2 45 59 32.5 36.5 37.2 60 65 8 7.9 8.9 Race/ethnicity White 71.4 76.6 78.3 Black 12 10.3 9.5 Hispanicà 11.6 7.8 7.2 Other 5 5.3 5.0 Education Less than 12.8 6.3 5.8 high school High school 31.7 24.6 24.8 Some college 28.4 39.8 39.8 Bachelor or higher 27.2 29.3 29.7 Participants (n ¼ 25 986) (%) * US Bureau of the Census (2002). Current Population Survey. http:// ferret.bls.census.gov/cgi-bin/ferret. Participants are defined as those who returned the questionnaire in a satisfactory manner. à Hispanic represents ethnicity. Individuals may have identified themselves as Hispanic and a race. 901 met the criteria for diarrhoea-predominant IBS, 333 met the criteria for constipation-predominant IBS and 453 had alternating IBS. Twenty-six participants were not classifiable and are included only in the overall totals. Of the IBS participants, 64% were female; 81% were white and 10% were black (see Table 2). Most IBS participants (66.9%) had at least some college education, and a majority of IBS participants (52.6%) were <44 years old (Table 2). Most (76.1%) of the IBS participants were employed, 81% were head of the household; 59.4% were married and 41.2% were earning $50 000 per year (Table 2). There was little variation in demographic characteristics across IBS subtypes. In the diarrhoea-predominant group, compared with other subtypes, there was a higher proportion of male participants and a higher proportion with lower incomes in the alternator subtypes. In addition, almost 15% of individuals with constipation-predominant subtype were disabled and,

938 E. B. ANDREWS et al. Table 2. Demographic characteristics of irritable bowel syndrome (IBS) participants completing the second questionnaire, and prevalence of IBS within each demographic group Demographic composition (%) within IBS subtype Prevalence (%) within each demographic stratum Demographic characteristics Diarrhoea (n ¼ 901) Alternator (n ¼ 453) Constipation (n ¼ 333) Overall (n ¼ 1713) Diarrhoea (n ¼ 901) Alternating (n ¼ 453) Constipation (n ¼ 333) Overall (n ¼ 1713) Overall NA NA NA NA 3.5 1.7 1.3 6.6 (6.3 6.9) Gender Male 39.0 32.9 29.1 34.9 2.8 1.2 0.8 4.7 (4.4 5.1) Female 61.0 67.1 70.9 63.6 4.1 2.3 1.8 8.2 (7.7 8.7) Education level Less than HS 5.0 7.9 9.3 6.5 3.0 2.4 2.1 7.4 (6.2 8.9) HS 23.9 25.6 29.4 25.0 3.3 1.8 1.5 6.7 (6.1 7.3) Some college 46.4 42.8 39.6 43.4 4.0 1.9 1.3 7.2 (6.7 7.7) Bachelor or higher 24.8 23.6 21.6 23.5 2.9 1.4 0.9 5.2 (4.7 5.8) Race/ethnicity White 85.5 78.8 79.9 81.3 3.6 1.6 1.2 6.4 (6.1 6.8) Black/African-American 8.1 13.2 13.2 10.3 2.8 2.3 1.7 6.8 (5.9 7.9) Other combined 6.2 6.2 6.0 6.1 3.5 1.8 1.3 6.6 (5.4 7.9) Latino/Hispanic 5.4 7.5 9.6 6.7 2.6 1.8 1.7 6.2 (5.2 7.4) Age <35 21.8 24.7 23.4 22.5 3.1 1.8 1.2 6.2 (5.6 6.8) 35 44 31.1 29.6 30.3 30.1 3.7 1.8 1.4 6.9 (6.3 7.5) 45 54 28.6 29.4 26.4 28.0 3.6 1.8 1.2 6.6 (6.0 7.2) 55+ 18.5 16.3 19.8 17.9 3.4 1.5 1.3 6.2 (5.5 6.9) Income <$20 000 14.7 23.2 21.0 17.9 3.9 3.1 2.0 9.0 (8.1 10.0) $20 000 $34 999 18.6 17.0 18.9 18.0 4.0 1.8 1.5 7.4 (6.6 8.2) $35 000 $49 999 22.2 19.9 21.3 21.1 3.7 1.6 1.3 6.6 (6.0 7.3) $50 000 $74 999 23.6 20.5 24.0 22.5 3.2 1.4 1.2 5.8 (5.2 6.4) $75 000+ 20.5 19.2 14.7 18.7 3.0 1.4 0.8 5.2 (4.7 5.8) Marital status Not married 37.8 44.4 37.8 39.0 3.9 2.3 1.4 7.7 (7.2 8.3) Married 62.0 55.4 62.2 59.4 3.24 1.4 1.2 5.9 (5.6 6.2) Employment status Working 81.5 78.6 64.0 76.1 3.4 1.2 1.0 5.9 (5.6 6.3) Not working 15.5 18.1 21.3 17.1 4.8 2.8 2.4 10.0 (8.9 11.1) Disabled 14.7 2.9 0.0 0.0 4.5 4.5 (3.4 5.9) Head of household No 15.9 20.3 15.6 16.8 3.8 2.5 1.4 7.7 (6.9 8.6) Yes 83.6 79.2 84.4 81.3 3.4 1.6 1.3 6.3 (6.0 6.6) compared with other subtypes, more frequently not working. Prevalence Table 2 presents prevalence of IBS and of the subtypes. The overall prevalence of IBS was 6.6% (CI: 6.3 6.9). The prevalence by subtype was 3.5% (CI: 3.3 3.7) for diarrhoea-predominant IBS; 1.3% (CI: 1.2 1.4) for constipation-predominant IBS and 1.7% (CI: 1.5 1.9) for alternators. Prevalence of IBS was similar across all race/ethnicity groups and was highest in persons without a high school education, especially in those individuals with alternating and constipation-predominant IBS. IBS prevalence increased as income decreased, with a 9.0% (CI: 8.1 10.0) prevalence among individuals with an annual income <$20 000 vs. 5.2% (CI: 4.7 5.8) in the highest income group. Unemployed individuals had a higher prevalence of IBS (10.0%, CI: 8.9 11.1) than those who were employed (5.9%; CI: 5.6 6.3). Prevalence was higher among unmarried

IBS PREVALENCE FROM A WEB-BASED SURVEY 939 individuals compared with married (7.7% vs. 5.9%) and was higher among individuals who were not head of household (7.7%) relative to those who were (6.3%). Physician consultation, medication use and surgeries The second questionnaire was sent only to diarrhoeapredominant and alternating patients. There were 1354 IBS participants with diarrhoea-predominant or alternating IBS, and 1180 (87%) of these satisfactorily completed the second questionnaire (phase 2 respondents, hereafter). A majority [66% (n ¼ 782)] of phase 2 respondents had symptoms consistent with diarrhoeapredominant IBS and 34% (n ¼ 398) had a pattern consistent with alternating IBS. During the year preceding the survey, 51% of phase 2 respondents saw a doctor about their abdominal symptoms. Women consulted physicians more frequently than men (54% vs. 47%). Thirty-five per cent of phase 2 respondents reported having been diagnosed with IBS, irritable colon, or spastic colon. Between the two IBS subtypes we observed no meaningful differences in the per cent with a previous IBS diagnosis; however, 43% of women and 21% of men (P < 0.0001) reported having one of these diagnoses. Twenty-two per cent of the phase 2 respondents had symptoms for more than 10 years: 15.1% between 6 and 10 years, 40.9% between 1 and 5 years, and 21% of subjects reported symptoms for <1 year. Of those who had symptoms >10 years, 56% had received a formal diagnosis of IBS, spastic colitis, or irritable colon, while only 15% of those that had experienced symptoms for <1 year had received a formal diagnosis. Approximately 67% of phase 2 respondents reported that their most recent episode occurred within the last 3 months. No meaningful differences between diarrhoea-predominant participants and alternators for any of the above parameters was noted. Figure 1 shows the type of physician consulted for IBS symptoms. Both men and women with diarrhoeapredominant or alternating IBS most often saw a family practitioner (23.5%), followed by a gastroenterologist (20%). Those with alternating IBS tended to consult physicians more frequently than those with diarrhoeapredominant disease. Use of at least one prescription therapy to treat IBS symptoms in the past year was reported by 46% of phase 2 respondents. H2-antagonists and antidiarrhoeals were the most frequently Figure 1. Type of physician subjects reported seeing for abdominal symptoms within the last 12 months [males are shown in the upper panel and females are shown in the lower panel. Alternating participants ¼ blackened bars and diarrhoea-predominant participants ¼ dotted bars]. reported medications. Ninety-one per cent also reported using over-the-counter (OTC) therapies during the past year. More than 60% of subjects reported using either an antidiarrhoeal or an antacid. Analgesics were used by approximately 50%, and over the 12-month period, phase 2 respondents used a mean of 4.0 categories of medications (prescription and OTC combined). Women were more likely than men to be using prescription medication (53% vs. 45%). Prescription or OTC medications were used to treat the spectrum of IBS symptoms, with 71.6% using drugs for the treatment of abdominal pain and discomfort, 52.4% for urgency, 53.4% for frequent bowel movements, 33.5% for infrequent bowel movements, 55.4% for loose watery stools and 31.9% for hard firm stools. In addition, 71.4% reported dietary changes as a treatment of their IBS symptoms, and 29.5% and 26.6% reported using stress reduction therapies and herbal remedies, respectively. Eleven per cent of respondents reported having, at some time, abdominal surgery for their abdominal symptoms. For females, 12% of diarrhoea-predominant respondents and 14% of alternators reported having surgeries. Lower frequencies were seen in males, with 10% of diarrhoea-predominant males and 8% of male alternators undergoing surgery related to their abdominal complaints.

940 E. B. ANDREWS et al. SF-36 On every domain of the SF-36, the functional status of phase 2 respondents was negatively impacted relative to US population norms (Figure 2). Subjects with a preexisting diagnosis of IBS were more affected on each domain (Figure 2). On a majority of domains, women reported a greater negative impact on quality of life than did men, and for most domains, diarrhoea-predominant participants and alternators were similarly affected. DISCUSSION Prevalence In the present study, an IBS prevalence of 6.6% was found. This prevalence is consistent with that reported in some other studies, but different from values found in others. A Canadian sample 32 reported a prevalence of 13.5% using Rome I and 12.1% using Rome II Criteria. In the US householder survey, 9 11% of those surveyed reported symptoms consistent with IBS. In a large survey (>41 000 patients) recently conducted in eight European countries 11 overall prevalence of IBS was 9.6%, and ranged from 6.2 to 12% across countries. The Rome Criteria are important tools for clinical trials and regulatory purposes but are not useful in everyday clinical practice. Thus, prevalence estimates for IBS based on the Manning or Rome Criteria may represent minimum estimates of the potential clinic populations. In a review of six large health surveys, 7 the prevalence of IBS in women was 3.2 times that in men. The present survey also identified a higher prevalence in women, with an approximately two times greater prevalence rate in women as compared with men. In the previously Figure 2. Effects of irritable bowel syndrome (IBS) on quality of life (The domains of the Short-Form 36 are shown on the horizontal-axis). mentioned review, 7 the prevalence of IBS in white individuals was 5.3 times the prevalence of black individuals, and prevalence was highest in those aged 45 64 years. In the present survey, whites had lower prevalence than, but not significantly different from, blacks or other race/ethnicity subgroups. To our knowledge, this study is the first to identify a relationship between measures of socioeconomic status (SES) and IBS prevalence. Individuals with lower income and less education had a higher prevalence of IBS than individuals with higher SES (e.g. higher income, higher education), and unmarried individuals and heads of households had a higher prevalence of IBS than married individuals and non-heads of households. While this study shows a higher prevalence of IBS among persons of lower income and education in the general population (Table 2), within the IBS population, the typical person tends to be white, female, approximately 44 years of age, married, employed, have had symptoms >1 year and have some college. These characteristics of typical IBS patients are similar to 9, 33 those observed in other studies. The strong relationship between IBS prevalence and lower SES within the general population suggests that some of the burden of IBS may be hidden from treating physicians, contrasting with the characteristics of the typical person with IBS. This may result from the large numbers of white, married and employed females in the general population. Even a low prevalence within a large population group could result in a large fraction of the IBS patients that physicians encounter. Burden of illness Recent studies have demonstrated the large negative impact that symptoms of IBS have on patients lives. 14 20 These studies used various disease-specific instruments, as well as the more general SF-36 that was used in the present study. Quality of Life data consistently show that, relative to US population norms, IBS patients experience negative impact on all or most domains of the SF-36. Furthermore, on domains of bodily pain, emotional well being, emotional functioning, energy/fatigue and social functioning, IBS has a greater impact than diabetes and is similar in effect to depression. 14 Results of the present study confirmed the large negative impact IBS symptoms have on participants lives in every domain and that women were affected to a greater extent than were men.

IBS PREVALENCE FROM A WEB-BASED SURVEY 941 Physicians and medications The patient burden of IBS is also reflected by physician visits, medication use and evaluative procedures. Everhart and Renault, 1 analysing office-based physician visit data from the National Ambulatory Medical Care Surveys, reported IBS to be the most common diagnosis made among gastroenterologists and the seventh leading diagnosis for all physicians. Prescriptions for medications were given at 75% of visits, and there was a high rate (at least 50%) of return appointments. Russo et al. 2 surveyed a sample from the American Gastroenterology Association, and IBS was the most common gastrointestinal disorder seen. In the present survey, over half of the participants with either diarrhoea-predominant or alternating disease reported seeing a physician about their IBS symptoms within the last 12 months. Approximately 65% reported their most recent episode occurred within the last 3 months. In the past 3 months, 46% and 91% of these participants had used at least one prescription and at least one OTC medication for treatment of IBS symptoms, respectively. These frequencies are similar to those reported in the US Householder Survey 9 where IBS patients averaged 1.64 physician visits per year for their gastrointestinal symptoms. In a recent community-based survey, 34 acid suppressants were found to be the medications most commonly prescribed to IBS patients, and this prescribing pattern was also seen in the present study. Hasler and Schoenfeld 25 reviewed the prevalence of abdominal and pelvic surgeries in IBS patients and reported an increased number of cholecystectomies, hysterectomies, appendectomies and other surgeries in IBS patients. In the present survey, 11% of IBS patients had abdominal surgery secondary to IBS symptoms. Web-based study There are several advantages to data collection using the web-based survey methodology: (i) information was obtained from a diverse sample, representative of the US population; (ii) data collection occurred rapidly, and: the web-based research panel is an existing panel for which a substantial amount of information already exists; and (iii) participants can be re-questioned if additional longitudinal follow-up is desired. Access to this population also enabled evaluation of prevalence within various demographic and socioeconomic groups. A disadvantage of the web-enabled methodology, as with other survey techniques, is the lack of access to clinical information. Additionally, a potential bias exists if some individuals do not participate in a web-based panel because of concerns about the technology. It is believed that these issues would not have a large impact on the conclusions drawn from this study. Because IBS is an episodic condition with symptoms that may change over time, sampling individuals at a single point in time is a potential disadvantage of this and other study methods. In conclusion, this study presents a new web-enabled technology for conducting prospective data collection in patients with IBS. ACKNOWLEDGEMENTS Funding was provided by GlaxoSmithKline and RTI Health Solutions. REFERENCES 1 Everhart JE, Renault PF. Irritable bowel syndrome in officebased practice in the United States. Gastroenterology 1991; 100: 998 1005. 2 Russo MW, Gaynes BN, Drossman DA. A national survey of practice patterns of gastroenterologists with comparison to the past two decades. J Clin Gastroenterol 1999; 29: 339 43. 3 Drossman DA, Camilleri M, Mayer EA, Whitehead WE. AGA technical review on irritable bowel syndrome. Gastroenterology 2002; 123: 2108 31. 4 Manning AP, Thompson WG, Heaton KW, Morris AF. Towards a positive diagnosis of the irritable bowel. Br Med J 1978; 2: 653 54. 5 Thompson WG, Creed F, Drossman DA, Heaton KW, Mazzacca G. Functional bowel disorders and functional abdominal pain. Gastroenterology Internat 1989; 5: 75 91. 6 Thompson WG, Longstreth GF, Drossman DA, Heaton KW, Irvine EJ, Muller-Lissner SA. Functional bowel disorders and functional abdominal pain. Gut 1999; 45(Suppl. II): II43 7. 7 Sandler RS. Epidemiology of irritable bowel syndrome in the United States. Gastroenterology 1990; 99: 409 15. 8 Jones R, Lydeard S. Irritable bowel syndrome in the general population. Br Med J 1992; 304: 87 90. 9 Drossman DA, Li Z, Andruzzi E, et al. US householder survey of functional gastrointestinal disorders: prevalence, sociodemography, and health impact. Dig Dis Sci 1993; 38: 1569 80. 10 Delvaux M. Functional bowel disorders and irritable bowel syndrome in Europe. Aliment Pharmacol Ther 2003; 18(Suppl. 3): 75 9. 11 Hungin APS, Whorwell PJ, Tack J, Mearin F. The prevalence, patterns and impact of irritable bowel syndrome: an international survey of 40,000 subjects. Aliment Pharmacol Ther 2003; 17: 643 50.

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