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| Journal of the New Zealand Medical Association,
25-October-2002, Vol 115 No 1164
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Prevalence and correlates of irritable bowel symptoms in a
New Zealand birth cohort
Gil Barbezat, Richie Poulton, Barry Milne, Stuart Howell, J
Paul Fawcett and Nicholas Talley
Functional gastrointestinal disorders (FGID) are encountered
frequently in clinical practice. They have been defined in very broad terms as a
group of variable chronic or recurrent gastrointestinal symptoms for which no
specific structural or biochemical explanation can be
found.1 Patients with FGID may present with
challenging clinical problems; their symptoms require careful evaluation to
differentiate those with functional disorders from those with organic disease.
Irritable bowel syndrome (IBS) is a subset of the FGID, focussing on chronic or
recurrent altered bowel habit and abdominal
pain.2 It has attracted much attention because
of its importance relating to patient morbidity and cost to the
community.3
As patients with IBS present with non-specific symptoms,
there is no gold standard for diagnosis. However, significant advances have been
made to define symptom complexes, which together with absence of clinical
abnormalities on a careful full clinical assessment allow the diagnosis of IBS
to be made with reasonable confidence. Manning et al defined four key symptoms
that were useful in discriminating patients with IBS from those with organic
gastrointestinal disorders.4 These were
distention, relief of pain with bowel movement, and looser and more frequent
stools with the onset of pain. Mucus per rectum and a sensation of incomplete
evacuation were also common in these patients. Others have subsequently
confirmed these findings.5,6 There have been a
number of reports by expert committees that have attempted to clarify the
symptoms most appropriate and accurate to act as diagnostic criteria for IBS.
The latest of these (known as Rome II) defines these as ‘at least 12
weeks, which need not be consecutive, in the preceding 12 months of abdominal
discomfort or pain that has 2 of 3 features: (1) relief with defecation; and/or
(2) onset associated with a change in frequency of stool; and/or (3) onset
associated with a change in form (appearance) of
stool.’2 However, many prefer to use the
tried and tested Manning criteria, which incorporate a broader range of
symptoms. It is no longer acceptable to regard IBS as a diagnosis of the
destitute, acting as a waste basket for all inexplicable bowel
symptoms.
Studies on population prevalence of gastrointestinal
symptoms have centred predominantly in Europe and the
USA.7–11 The prevalence of IBS has been
extrapolated from these data. It is suspected that gastrointestinal symptoms are
as common in New Zealand as in those countries, but there are no reliable data
to validate this presumption. Although the original symptom criteria were not
designed for screening purposes, a validated questionnaire has been developed
from them which has been useful in identifying patients with
IBS.12 This symptom-based questionnaire has
been applied to participants in the Dunedin Multidisciplinary Health and
Development Study.13 This provided an ideal
opportunity to study a large birth cohort of subjects at an age (26 years) when
IBS is known to be prevalent from previous
studies.9
MethodsParticipants were 499 male and
481 female (mean age 26.0 years) members of the Dunedin Multidisciplinary Health
and Development Study, a longitudinal investigation of the health, development
and behaviour of 1037 children born in Dunedin during
1972–73.13 Cohort families represent the
full range of socioeconomic status in the general population of New
Zealand’s South Island and are primarily of European descent. Ninety six
per cent of the living sample (980/1019) participated in the
‘age-26’ assessment between March 1998 and July 1999. The basic
procedure involves bringing participants to the Research Unit for a full day of
individual data collection.
As part of the day’s assessments, participants were asked to complete the Bowel Disease Questionnaire (BDQ). The BDQ consists of 46 gastrointestinal symptom-related items, and has been shown to be an understandable, easily completed, and highly reliable (median k = 0.78) diagnostic tool; it has also been shown to have adequate content, predictive and construct validity.12,14 Partial information was available for 975 participants and complete information for 965 (an indication of the variation in sample size across items can be obtained from the sample numbers given in Table 1). Most participants completed the BDQ themselves, although those participants who were known from previous assessments to be below the 10th percentile in terms of reading ability had the questionnaire read to them and their answers recorded by an interviewer. Participants were classified into several a priori symptom categories based on their responses to the questionnaire, which recorded their symptoms over the previous year. Abdominal pain Persons who reported having had abdominal pain in the prior year, and who indicated that their pain was not due to an acute illness or side effect of medication, were defined as having abdominal pain. Pain was further subdivided into ‘colonic pain’, defined as pain relieved >25% of the time by defecation and/or associated with looser and/or more frequent stools at its onset. These symptoms comprise items from the Manning criteria that have been shown to be characteristic of IBS.1,4,5 The remainder with pain were classified as having non-colonic pain. Chronic constipation Persons who strained at stool and who passed hard stools and/or those whose bowel habit was <3 stools per week >25% of the time were defined as having chronic constipation. Painless constipation was defined as constipation in the absence of abdominal pain not due to acute illness or medication side effects in the prior year. Chronic diarrhoea Persons who passed loose or watery stools and/or whose stool frequency was >3 stools per day >25% of the time were defined as having chronic diarrhoea. Painless diarrhoea was defined as diarrhoea in the absence of abdominal pain not due to acute illness or medication side effects in the prior year. Table 1. Prevalence of colonic symptoms in 26-year-old
Dunedin Multidisciplinary Health and Development Study participants
(data represent prevalence per 100 (95% CI);
often = >25% of the time)
*Manning symptom criteria for IBS
Identification of
symptoms compatible with the irritable bowel syndrome (Manning criteria)
This category included persons who experienced abdominal pain not due to acute
illness or medication side effects in the prior year, in combination with two or
more of the following: 1) pain that was relieved by defecation >25% of the
time; 2) looser stools when pain began >25% of the time; 3) more frequent
stools when pain began >25% of the time; 4) abdominal distention >25% of
the time; 5) feeling of incomplete evacuation >25% of the time; and 6) mucus
per rectum. It has been shown that the more criteria that are present, the
higher the probability of IBS.4,5 Based on the
available literature, we used a cut-off score of two or more criteria to
identify symptoms compatible with IBS. This has a sensitivity of 94% and a
specificity of 55%. The presence of three or more criteria has a sensitivity and
specificity of 84% and 76%
respectively.4
Statistical analysis Logistic regression analyses were used to assess the association between sex and symptoms, and the presence or absence of colonic pain, chronic constipation, chronic diarrhoea, and IBS. The estimated parameters for specific symptoms in the logistic regression models, which also contained sex as an independent variable, are used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the symptoms. The α level of significant was set at 0.05; all p values calculated were two-tailed. ResultsOf the symptoms measured, 64% of
the sample participants had experienced at least one in the prior year. The
overall and sex-specific prevalence rates of individual symptoms are presented
in Table 1.
Abdominal pain
Abdominal pain was reported by 453 (46.5%) participants (Table 2). A
logistic regression analysis, adjusting for sex, identified a number of
characteristic features associated with colonic pain (n = 201) vs non-colonic
pain (n = 242) (Table 2). Persons with colonic pain were significantly more
likely than those with non-colonic pain to report pain in the lower abdomen,
abdominal distention and a disturbance of defecation characterized by mucus per
rectum, straining, loose or watery stools, rectal urgency and frequent (>3
per day) stools. In contrast, persons with non-colonic pain were more likely to
report pain in the upper abdomen. Severity and duration of pain were similar in
those with colonic and non-colonic pain, as were the proportions reporting hard
or infrequent (<3 per week) stools.
Table 2. Characteristics of
bowel symptoms in 26-year-old DMHDS participants with and without abdominal and
colonic pain (colonic pain = pain in prior year relieved by defecation,
and/or associated with looser and/or more frequent stools at pain onset; often =
>25% of the time)
*Adjusted for gender from logistic regressions with
abdominal pain (colonic abdominal pain, non-colonic abdominal pain, no abdominal
pain) as the dependent variable
Constipation and
diarrhoea Eighty nine (9.1%) participants reported chronic constipation
and 166 (17.1%) reported chronic diarrhoea (Table 3).
Table 3. Prevalence of symptom categories among DMHDS
participants
A comparison of the symptoms in these groups is presented in
Table 4. Those with chronic constipation and those with chronic diarrhoea were
significantly more likely to report abdominal distention as well as other bowel
symptoms, including mucus per rectum, a feeling of incomplete evacuation and
urgency. Persons with diarrhoea, but not those with constipation, were more
likely to report abdominal pain. In those with chronic constipation and
diarrhoea, 28% and 41% respectively had two or more symptoms characteristic of
IBS.
Table 4. Characteristics of abdominal pain and bowel
symptoms in subjects with and without chronic constipation and diarrhoea
(constipation = straining at stool and hard
stools and/or <3 stools per week more than 25% of the time; diarrhoea =
loose, watery stools and/or >3 stools/day more than 25% of the
time)
*Adjusted for gender from logistic regressions with
constipation or diarrhoea (vs no constipation or no diarrhoea) as the dependent
variable; † p<0.05;
‡ p <0.01;
§ p <0.001
Symptoms compatible with
IBS The prevalence rate for IBS in this sample is shown in Table 3. Of
the six Manning symptom criteria for IBS, 33% of the sample reported one or more
of the complaints. Defining IBS as two or more of the six Manning criteria in
those with abdominal pain not due to acute illness or medication side effects in
the prior year, the prevalence of IBS was 18.8% (95% CI, 16.3–21.3). The
estimated prevalence rate decreased to 10.3% if three or more Manning criteria
symptoms were required to fulfil the definition, and to 3.3% if four or more
symptoms were required. Regardless of the definition used, prevalence rates were
higher for women than men (two or more symptoms: OR = 1.7, 95% CI =
1.2–2.4; three or more symptoms: OR = 1.7, 95% CI = 1.1–2.5; four or
more symptoms: OR = 2.8, 95% CI = 1.3–6.0). The sex-specific proportions
for each of the Manning criteria are shown in Figure 1. There were elevated
prevalence rates for women for each of the six criteria.
Sex differences
Compared with men, women were more likely to report any IBS symptom (OR =
2.2, 95% CI = 1.7–2.9) and that they experienced abdominal pain (OR = 2.2,
95% CI = 1.7–2.9). Women also were more likely than men to report the
following symptoms: moderate or worse pain severity (OR = 3.0, 95% CI =
2.2–4.2); looser stools at pain onset (OR = 1.9, 95% CI = 1.2–2.8);
lower abdominal pain (OR = 2.8, 95% CI = 2.1–3.9); mucus per rectum (OR =
5.0, 95% CI = 2.9–8.8); infrequent (<3 per week) stools (OR = 2.1, 95%
CI = 1.3–3.4); straining (OR = 2.5, 95% CI = 1.5–4.3); urgency (OR =
2.2, 95% CI = 1.2–3.9); bloating (OR = 5.1, 95% CI = 2.9–8.9); and
chronic constipation (OR = 2.2, 95% CI = 1.4–3.5).
Figure 1. The sex-specific proportions for each of six
symptoms composing the Manning criteria for IBS in persons with abdominal pain
not due to acute illness or medication side effects in the prior year
 1 = pain relieved by defecation often; 2 = increased
stool frequency at pain onset often; 3 = looser stools at pain onset often; 4 =
abdominal distention often; 5 = feeling of incomplete evacuation often; 6) mucus
per rectum
DiscussionThis study has shown that abdominal
symptoms are very common in a community cohort of young New Zealanders aged 26
years. As many as 64% of them had at least one symptom in the previous year.
This is almost identical to an older American cohort studied with similar survey
material (68%).7 A significant number of these
have symptoms fulfilling the well defined Manning criteria fitting a diagnosis
of IBS.4 In this birth cohort, 18.8% fulfilled
at least two, 10.3% at least three, and 3.3% at least four of the six Manning
criteria. These results are similar to those from a comparable study in the USA
by Talley et al who found a prevalence of 17.0%, 12.8% and 8.7% for each of the
frequencies of diagnostic criteria.7 However,
that study was performed by postal survey on an older group of subjects
(30–64 years). A smaller, community-based study from the UK by Thompson
and Heaton described 13.6% of subjects having symptoms compatible with IBS; when
these were split into young (17–27 years), middle-aged (45–65
years), and older (60–91 years) age groups, the respective prevalences
were 19.2%, 7.2% and 14.0%.8 Another USA-based
study by Drossman et al found 17.1% of 789 community subjects of mean age 24
years with bowel function suggesting IBS.9
Population prevalence therefore appears very similar amongst New Zealanders when
compared with that in the USA and UK.
Participants in this study comprise 96% of a complete birth
cohort who have now been followed up for 26 years. Most of them are experienced
in responding to questionnaires, with a small minority requiring additional
help. This was provided by staff trained and experienced in this
field.13 Symptoms were defined clearly and the
questionnaire used has been validated. We believe the results accurately reflect
the pattern of clinical symptoms among young people in the general population.
As there is no gold standard for diagnosis of IBS, other conditions (eg
inflammatory bowel disease, coeliac disease) cannot be excluded entirely.
However, the prevalence of these disorders in the community is low and therefore
unlikely to significantly distort the number thought to have
IBS.6,15
The previously described female preponderance of IBS has
been confirmed in this cohort of subjects. Not only were the features of IBS
more common in females, but abdominal pain, loose stools, passage of mucus per
rectum, urgency, straining at stool, infrequent stools and constipation were at
least twice as common than in males. Bloating was even more common in females
(OR 5.1, CI 2.9–8.9) but the reasons for this are probably
multifactorial.
As confirmed in this study, there are a wide range of
abdominal symptoms among those surveyed in the community. Interestingly, lower
abdominal pain was more frequently related to disturbance in bowel habit, while
upper abdominal pain was less likely to be related to alterations in bowel
habit. This is consistent with IBS representing a spectrum of pathophysiological
disorders that could be linked in their clinical
presentation;16,17 some of these have been
linked to psychosocial factors.18,19 These are
to be reported in a further analysis of the extensive lifelong developmental
data available on this cohort.
Author information:
Gil O Barbezat, Professor of Medicine, Department of Medicine; Richie Poulton,
Director; Barry J Milne, Research Fellow, Dunedin Multidisciplinary Health and
Development Research Unit, Department of Preventive and Social Medicine, Dunedin
School of Medicine, Dunedin; Stuart Howell, Research Fellow, Department of
Medicine, University of Sydney, Sydney, Australia; J Paul Fawcett, Senior
Lecturer, School of Pharmacy, University of Otago, Dunedin; Nicholas J Talley,
Professor of Medicine, Department of Medicine, University of Sydney, Sydney,
Australia
Acknowledgements: We
thank the Dunedin study members and their parents, Unit research staff, Air New
Zealand, and Study founder, Phil Silva. The Dunedin Multidisciplinary Health and
Development Research Unit is supported by the Health Research Council of New
Zealand.
Correspondence:
Professor G O Barbezat; Department of Medicine, Dunedin School of Medicine, P O
Box 913, Dunedin. Fax: (03) 474 7724; email: gil.barbezat@stonebow.otago.ac.nz
References:
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