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Irritable Bowel Syndrome in the United States: Prevalence, Symptom Patterns and Impact
      07/05/05 03:40 PM

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From Alimentary Pharmacology & Therapeutics

Irritable Bowel Syndrome in the United States: Prevalence, Symptom Patterns and Impact

A. P. S. Hungin; L. Chang; G. R. Locke; E. H. Dennis; V. Barghout

Summary and Introduction
Background: The impact of irritable bowel syndrome, a gastrointestinal motility disorder, is underestimated and poorly quantified, as clinicians may see only a minority of sufferers.
Aim: To determine the prevalence, symptom patterns and impact of irritable bowel syndrome in the US.
Methods: This two-phase community survey used quota sampling and random-digit telephone dialling (screening interview) to identify individuals with medically diagnosed irritable bowel syndrome or individuals not formally diagnosed, but fulfilling irritable bowel syndrome diagnostic criteria (Manning, Rome I or II). Information on irritable bowel syndrome symptoms, general health status, lifestyle and impact of symptoms on individuals' lives was collected using in-depth follow-up interviews. Data were also collected for healthy controls identified in the screening interviews.
Results: The total prevalence of irritable bowel syndrome in 5009 screening interviews was 14.1% (medically diagnosed: 3.3%; undiagnosed, but meeting irritable bowel syndrome criteria: 10.8%). Abdominal pain/discomfort was the most common symptom prompting consultation. Most sufferers (74% medically diagnosed; 63% undiagnosed) reported alternating constipation and diarrhoea. Previously diagnosed gastrointestinal disorders occurred more often in sufferers than non-sufferers. Irritable bowel syndrome sufferers had more days off work (6.4 vs. 3.0) and days in bed, and reduced activities to a greater extent than non-sufferers.
Conclusions: Most (76.6%) irritable bowel syndrome sufferers in the US are undiagnosed. Irritable bowel syndrome has a substantial impact on sufferers' well-being and health, with considerable socioeconomic consequences.

Irritable bowel syndrome (IBS) is a chronic, episodic functional gastrointestinal (GI) disorder characterized by abdominal pain/discomfort and altered bowel habit (constipation, diarrhoea or alternating periods of both).[1] Patients often experience additional symptoms such as bloating, sensation of incomplete evacuation, straining (constipation) and urgency (diarrhoea). IBS patients can experience symptoms for many years, with an average duration of 10 or more years.[1,2] IBS is often unrecognized or untreated, with as few as 25% of IBS sufferers seeking professional health care.[3] Those seeking care are often frustrated by the lack of effectiveness of traditional treatment and management strategies.[4]

IBS prevalence is estimated to be 10-15% in Western countries.[5-9] Prevalence data and information on the health care-seeking behaviour of IBS sufferers have mostly been derived from independent studies using different methodologies and different diagnostic criteria. As there are no IBS-specific biological markers to aid diagnosis, doctors generally rely on symptom-based criteria. At least three sets of diagnostic criteria have been developed, including the Manning,[10] Rome I[11] and Rome II criteria.[12] The Rome I and II criteria are more refined than the Manning criteria, and include symptom duration within their definitions. Variations in study design, particularly the criteria used to diagnose IBS, affect the ability to compare or summarize data from multiple studies.[13]

One challenge of population-based IBS studies is ensuring that IBS is accurately diagnosed using specific, validated criteria, rather than the clinical judgement of health care professionals.[7]

IBS places a significant financial burden on society. Symptoms can significantly impact on the quality of life of sufferers, with considerable socioeconomic consequences.[14-18] For example, absenteeism from work is more prevalent in individuals with IBS than in those without,[1,19] and employers in the United States (US) are estimated to pay, on average, $1251 more for individuals with IBS than matched control beneficiaries over a 1-year period ( P < 0.001).[20]

A recent European study investigated the prevalence, symptom pattern and impact of IBS across eight countries in an attempt to define the magnitude of the problem facing health care providers.[21] The present study, which used the same methodology, evaluated IBS prevalence, symptom pattern and impact on work, social activities and well-being of sufferers in the US. Attitudes towards the health and consultation behaviour of IBS sufferers were also assessed.

Materials and Methods
Survey Methodology
A random-digit dialling technique as described previously[21] was used to identify study participants. This technique has proven feasibility and accuracy in health research[22-24] and enhances the representativeness of the study. Random-digit dialling allowed large numbers of people in the US to be easily identified while avoiding the possibility of cluster sampling often seen with multiple fixed-site surveys. Sampling limitations often noted with postal surveys were also avoided. Research supports this technique as a highly efficient way of yielding accurate data.[22-24]

This methodology assumed that more than 90% of the US households had a telephone and that approximately 25% of numbers were unlisted. Random-digit dialling sampling enabled numbers in the US to be assigned with a probability of selection. As previously described,[21] a random initial sample was drawn from all known listings using a 1 in n sampling interval and an algorithm was then utilized to randomize the last two digits, thus ensuring the inclusion of unlisted numbers. All telephone numbers were prescreened for a valid dialling tone to maximize data efficiency. All fieldwork was conducted on weekday evenings and weekends so that the working population was represented in the study. In order to enhance representativeness, quota sampling was applied in terms of age and gender. This survey was carried out by The Sample Surveys Research Group (now Synovate), West Malling, UK, and commissioned by Novartis Pharmaceuticals, New Jersey, US.

Development and Application of the Questionnaires
The survey included two questionnaires and was executed in two phases; the development of the original questionnaires has been previously described.[21] The first questionnaire was subjected to five stages of piloting and testing, including respondent validation. Further validation was conducted using clinicians and lay individuals in the US - terminology modification ensured respondent comprehension. The revised US version was piloted amongst 'live' respondents prior to commencement of fieldwork. The locally derived and adapted questionnaire was then tested in the US using the telephone interview technique.

In the first phase, a screening questionnaire was employed to identify subjects already diagnosed with IBS (medically diagnosed by their clinician) and to elicit information that identified non-diagnosed IBS sufferers according to the Manning, Rome I or Rome II diagnostic criteria. Subjects were classified as having undiagnosed IBS if they confirmed that they suffered from at least two of the Manning criteria and experienced abdominal pain/discomfort at least once in every 2 months in the previous 12 months. The screening questionnaire was presented to potential participants as being part of a general health project in order to avoid introducing bias and directing responses towards IBS or other GI conditions.

Patients were defined as having IBS with constipation (IBS-C) if they experienced one or more of the following: harder/more lumpy stools than usual, the need to pass stools less often than usual (<3 times/week), or periods of straining, which was not accompanied by the need to pass stools more often than usual (>3 times/day), looser/more watery stools than usual and periods of urgency. Patients were defined as having IBS with diarrhoea (IBS-D) if they experienced one or more of the following: looser/more watery stools than usual, the need to pass stools more often than usual (>3 times/day), or periods of urgency, which were not accompanied by the need to pass stools less often than usual (<3 times/week), harder/more lumpy stools than usual and periods of straining. Patients with other bowel habit patterns were defined as having alternating IBS (IBS-A). Differentiation into these specific IBS subtypes was based only on the symptoms suffered by each respondent, without reference to a specific time frame.

In the second phase of the survey, respondents who were identified as having IBS in phase I of the survey, either medically diagnosed or diagnosed using IBS criteria (Manning, Rome I or Rome II), were invited to participate in a more formal interview regarding their symptoms, general health factors, lifestyle and impact of IBS symptoms on their lives. Data on comorbid conditions, therapy/medication use and consultation patterns were also collected. Thus, three groups of respondents were identified: those with medically diagnosed IBS; those who had IBS that had not been medically diagnosed, but who fulfilled IBS diagnostic criteria; and a healthy comparator group identified from the screening questionnaire as not having IBS. Any individuals who had experienced IBS symptoms within the previous 12-month period were identified as current IBS sufferers.

For symptoms of constipation or diarrhoea, individuals were questioned (based onthe IBS diagnostic criteria) about: any periods needing to pass stools more often than usual (>3 times/day) or less often than usual (<3 times/week); any periods when stools were looser/more watery than usual or harder/more lumpy than usual; periods of straining when going to pass a stool; periods of urgency when going to pass a stool; feeling of incomplete evacuation after passing a stool; periods of bloating.

As in the European study,[21] the development of the questionnaire used in the US population incorporated the clinical experience of the clinicians involved with this study. Alternative diagnoses (not IBS) were excluded at an early stage of the questionnaire and pilot research was performed to ensure the Manning and Rome I/II criteria were effective in this setting. The questionnaire was designed and carefully validated to avoid order effects, such as suggestion based on earlier questions.

Based on the assumption of a conservative IBS prevalence rate of 5-10%, it was estimated that 5000 respondents would need to be contacted to reach 250-500 IBS sufferers in the US. Specific target age groups for the population were 18-34, 35-54 and over 55 years, with equal numbers contacted within these age groups.

The study was carried out in the US in a sample of subjects aged 18 years or over. Those previously diagnosed with Crohn's disease, ulcerative colitis, coeliac disease, diverticulitis, peptic ulcer or cancer (including colon and gynaecological cancers) were excluded from the results because of possible overlap with IBS symptoms.

From approximately 14 000 initial telephone contacts, a total of 5009 screening interviews were conducted; all questions in this section were related to general health. Among these, 708 individuals were identified as having current IBS (any diagnostic criteria) and, from this group, 318 individuals participated in the second phase of the questionnaire (366 individuals either did not want to take part in the second phase of the questionnaire or did agree but were not available when contacted).

Prevalence, Characteristics and Symptom Patterns of IBS (Medically Diagnosed and Not Medically Diagnosed)
Overall 708 individuals (14.1% of total screened) were identified as having current IBS [medically diagnosed ( n = 166; 3.3%) or met any diagnostic criteria (not medically diagnosed; n = 542; 10.8%)]. Results from this questionnaire are shown in Table 1 .

In general, medically diagnosed IBS patients reported a greater prevalence of individual IBS symptoms. The Manning criteria identified all current IBS sufferers (100%); the Rome I criteria identified 73% and the Rome II criteria identified 62%. Thus, only partial overlap of the IBS diagnosis was seen across these diagnostic criteria. The Rome II criteria appeared to be the most restrictive set. Of those individuals who had been medically diagnosed with IBS, 4% were deemed to have IBS-C compared with 21% with IBS-D. In those not medically diagnosed, these percentages were 15% and 21%, respectively. Most individuals with IBS (74% of those medically diagnosed and 63% not medically diagnosed) reported alternating symptoms of constipation and diarrhoea (IBS-A). When IBS sufferers were asked to categorize themselves according to these three subgroups, only approximately one-third of individuals medically diagnosed and not medically diagnosed with IBS defined themselves as having IBS-A (33% and 27%, respectively) compared with IBS-C (17% and 30%, respectively) and IBS-D (45% and 29%, respectively).

Age/Sex Distribution of Current IBS Sufferers (Medically Diagnosed and Not Medically Diagnosed)
Overall, the peak ages for current IBS symptoms were between 25 and 54 years (67.3% of IBS total; Table 1 ). IBS was more common in women than men (64% vs. 36%, respectively), particularly among those who had been medically diagnosed with IBS (81.3% vs. 18.7%, respectively). The highest prevalence of IBS was seen in working women, with a prevalence of 21% (5% medically diagnosed, 16% not medically diagnosed).

Comorbid Conditions
Current IBS sufferers (both medically diagnosed and not medically diagnosed) were more likely to have suffered from other GI disorders of function (previously diagnosed by a doctor) compared with non-IBS sufferers. IBS sufferers were twice as likely to suffer from gastro-oesophageal reflux disease (GERD; 22% vs. 10%, P < 0.001) compared with non-IBS sufferers.

Duration and Patterns of Symptoms
Results of the second phase of this study confirmed that IBS is a chronic disorder, with 16% of current IBS sufferers being medically diagnosed with the condition in the previous 12-month period, 8% in the previous 13-24 months, 26% in the previous 2-5 years and 14% 6-10 years ago. Overall, one-third of current IBS sufferers had had IBS for more than 10 years.

Although respondents had IBS for considerable periods of time, IBS symptoms remained fairly constant over time with 73% of medically diagnosed IBS sufferers reporting that their symptoms had never changed. Only 22% of current IBS sufferers reported some degree of symptom improvement since the screening interview. Current IBS sufferers typically experienced symptoms for an average of 8.1 days/month and reported a wide range of symptoms, with abdominal pain/discomfort being the most commonly reported (90%; Figure 1). The majority (71%) described their overall IBS symptoms as fairly or very painful. On each day with current symptoms (designated as a 'suffering day'), respondents with IBS had an average of 2.4 episodes of IBS. These episodes varied in duration but more than half (52%) of current sufferers experienced episodes more than 60 min in duration. More than half (64%) of individuals with current IBS symptoms believed that an episode of IBS was triggered by a certain food or drink while 30% cited stress as the trigger.

There appeared to be a gender difference in the reporting of IBS-related symptoms in current IBS sufferers. Women were more likely to report constipation, bloating, trapped wind, swollen tummy, tightness of clothing and tiredness. There were no differences in prevalence of abdominal pain, diarrhoea and heartburn between men and women with IBS.

Impact of IBS on Work, Lifestyle and Health
Responses from current IBS sufferers (medically diagnosed and not medically diagnosed) indicate that IBS negatively impacted upon a wide range of daily activities. Work productivity, particularly the ability to concentrate, and time management, was significantly affected in respondents with IBS compared with individuals without IBS (Figure 2; P = 0.01). The proportion of men and women reporting an impact was not significantly different.

In the 12 months prior to the survey, IBS sufferers had more time off work, spent more days in bed and cut down on usual activities on more days compared with non-IBS sufferers. Nearly one-quarter of IBS respondents worked fewer hours, 11% missed work and 67% felt less productive when at work because of their symptoms. Two-thirds of current IBS sufferers had cut back on the number of overall activities during the previous 12-month period for an average of 15 days. The average number of days affected by ill health leading to absenteeism was 6.4 vs. 3.0 days (current IBS sufferers vs. non-IBS sufferers). Overall, current IBS sufferers were twice as likely to spend at least 1 day in bed or cut back on usual activities compared with non-IBS sufferers. Nearly one-quarter of current IBS sufferers had missed social engagements.

IBS symptoms also had a significant impact on social well-being and daily social activities among sufferers compared with non-sufferers ( P = 0.01). Undertaking long journeys, going out for a meal and going on holiday were all noted as more of a problem for IBS sufferers than controls (Figure 3a; P = 0.01). In addition, diet and food choice were also adversely affected by current IBS symptoms (Figure 3b; P = 0.01 vs. individuals without IBS). IBS sufferers reported a wide range of effects of symptoms on daily life (>/=5 points on a scale of 0 = no impact to 10 = significant impact), in particular many felt they had to be either near a toilet or make frequent trips to the toilet (Figure 4). Again, the proportion of men and women reporting an impact was not significantly different.

Current IBS sufferers were more likely to perceive themselves as having poor health; compared with 54% of non-IBS sufferers, only 35% of IBS sufferers described themselves as having good health. More than half (57%) of all current IBS sufferers questioned felt that they would have more control over their life without IBS symptoms. An impact of health on relationships was also more evident amongst current IBS sufferers compared with non-IBS sufferers: more IBS sufferers found it difficult to make new friends (46% vs. 40%, P < 0.001) and have physical relationships (52% vs. 41%, P < 0.001), and they felt that their IBS symptoms affected family relationships (48% vs. 40%, P < 0.001).

Attitudes to Condition

In general, the attitude towards health and overall quality of life appeared to be affected to a greater extent in medically diagnosed patients than in IBS sufferers who were not medically diagnosed ( Table 2 ).

Current IBS sufferers commonly informed their partner about their condition (68%). Although they also often told other family members (56%) and friends (54%), they were less likely to inform colleagues (22%) or their employer (16%). Most confidants were deemed to be very (44%) or fairly (39%) understanding. Overall, one-quarter of IBS sufferers highlighted that their self-confidence was reduced as a result of IBS; this was particularly evident among the medically diagnosed group (46% vs. 17% of those not medically diagnosed). The majority (87%) of respondents medically diagnosed with IBS believed their IBS to be a real medical condition, compared with only 43% of individuals not medically diagnosed ( Table 2 ). As an indication of desire for effective therapy, nearly half of current IBS sufferers (46%) agreed that they would try 'anything' to alleviate their IBS symptoms.

Consultation Pattern and Health Care Use
A primary care doctor was the most common health professional seen by current IBS sufferers (83%); gastroenterologists were the next most commonly consulted group (40%; Table 2 ). Abdominal pain/discomfort was the most common reason for consulting a health professional (28% of consultations), followed by symptom frequency (10%). Current IBS sufferers had seen a doctor or nurse an average of 4.2 times in the past 12 months if medically diagnosed or 1.3 times if not medically diagnosed. More than half (53%) of respondents not medically diagn