A common, symptom-based case definition for gastroenteritis

Article (PDF Available)inEpidemiology and Infection 136(7):886-94 · July 2008with54 Reads
DOI: 10.1017/S0950268807009375 · Source: PubMed
Abstract
National studies determining the burden of gastroenteritis have defined gastroenteritis by its clinical picture, using symptoms to classify cases and non-cases. The use of different case definitions has complicated inter-country comparisons. We selected four case definitions from the literature, applied these to population data from Australia, Canada, Ireland, Malta and the United States, and evaluated how the epidemiology of illness varied. Based on the results, we developed a standard case definition. The choice of case definition impacted on the observed incidence of gastroenteritis, with a 1.5-2.1 times difference between definitions in a given country. The proportion of cases with bloody diarrhoea, fever, and the proportion who sought medical care and submitted a stool sample also varied. The mean age of cases varied by <5 years under the four definitions. To ensure comparability of results between studies, we recommend a standard symptom-based case definition, and minimum set of results to be reported.
A common, symptom-based case definition for gastroenteritis
S. E. MAJOWICZ
1
,
2
,G.HALL
3
, E. SCALLAN
4
*, G. K. ADAK
5
,C.GAUCI
6
,
T. F. JONES
7
,S.OBRIEN
8
,O.HENAO
4
, P. N. SOCKETT
1
,
2
, for the International
Collaboration on Enteric Disease Burden of Illness Studies
1
Foodborne, Waterborne, and Zoonotic Infections Division, Public Health Agency of Canada, Guelph
and Ottawa, ON, Canada
2
Department of Population Medicine, University of Guelph, Guelph, ON, Canada
3
National Centre for Epidemiology and Population Health, Australian National University, Canberra, Australia
4
Enteric Diseases Epidemiology Branch, Centers for Disease Control and Prevention, Atlanta, GA, USA
5
Department of Gastrointestinal Infections, Health Protection Agency Centre for Infections, London, UK
6
Disease Surveillance Unit, Department of Public Health, Msida, Malta
7
Tennessee Department of Health, Nashville, TN, USA
8
Division of Medicine & Neurosciences, University of Manchester School of Medicine, Manchester, UK
(Accepted 11 July 2007 ; first published online 9 August 2007)
SUMMARY
National studies determining the burden of gastroenteritis have defined gastroenteritis by its
clinical picture, using symptoms to classify cases and non-cases. The use of different case
definitions has complicated inter-country comparisons. We selected four case definitions from the
literature, applied these to population data from Australia, Canada, Ireland, Malta and the
United States, and evaluated how the epidemiology of illness varied. Based on the results, we
developed a standard case definition. The choice of case definition impacted on the observed
incidence of gastroenteritis, with a 1
.
5–2
.
1 times difference between definitions in a given country.
The proportion of cases with bloody diarrhoea, fever, and the proportion who sought medical
care and submitted a stool sample also varied. The mean age of cases varie d by <5 years under
the four definitions. To ensure comparability of results between studies, we recommend a
standard symptom-based case definition, and minimum set of results to be reported.
INTRODUCTION
Acute gastroenteritis is an important public health
issue worldwide [1–4]. In developed countries, while
mortality is low, the associated morbidity remains
high [5–8]. In order to better estimate the true level
of morbidity in the community, several countries have
conducted population-based studies [9–22]. Using
prospective and retrospective methodologies, these
studies have collected self-reported information from
random samples of their target populations, including
information on gastrointestinal symptoms (vomiting
and diarrhoea) and their severity, secondary symp-
toms, pre-existing conditions, health-care use and
burden, possible causes, and demographics. In these
studies, gastroenteritis refers to the acute onset of
enteric symptoms unrelated to existing health
conditions, medication use, or other non-infectious
causes, and is defined by its clinical picture, with
* Author for correspondence : Dr E. Scallan, 1600 Clifton Road
NE MSD63, Atlanta, GA 30333, USA.
(Email : escallan@cdc.gov)
Epidemiol. Infect. (2008), 136, 886–894. f 2007 Cambridge University Press
doi:10.1017/S0950268807009375 Printed in the United Kingdom
symptom-based case definitions used to classify
individuals as cases or non-cases. These case defi-
nitions are designed and used to estimat e total mor-
bidity, not as part of ongoing public health
surveillance of enteric disease.
Comparing the results of such studies is compli-
cated because both the terms used for the illness
and the symptom-based case defi nitions vary, despite
the fact that the studies are essentially evaluating
the same phenomenon. This problem, although
widely noted in the literature [1, 10, 12, 15, 16, 19,
20–22] has only been explored in a preliminary
fashion using data from one country [23, 24]. Ulti-
mately, a common, validated case definition and
common set of reported results are needed to en-
sure comparability across population-based studies
of gastroenteritis and to provide a credible estimate
of the global burden of disease.
The current lack of a standard definition is due,
in part, to the subjectivity of gastroenteritis as a
syndrome. Addit ionally, it stems from the need for
individual studies to be able to tailor their case defi-
nition to their specific purposes (e.g. diarrhoeal dis-
ease vs. acute gastrointestinal illness), to make their
case de finition and thus their data consistent with
other previously collected da ta within their country,
and to work within existing administrative, research,
or other frameworks. Most studies already collect
data in a manner which would allow more than
one symptom-based case definition to be applied
post hoc, although not all studies have collected
all specific data items which could be important.
Future studies could easily adapt data collection
to en able the application of any study-specific case
definitions, as well as a commonl y agreed standard
definition for internationa l comparison purposes.
The objectives of our investigation were to:
(a) demonstrate the impact of using different
symptom-based case definitions on the ob-
served epidemiology of gastro enteritis ;
(b) assess the feasibility of developing case defi-
nition multipliers for use in adjusting for
variation in incidence rates among studies;
and
(c) recommend a standard, symptom-based case
definition for gastroenteritis, along with a
minimum set of results to be reported under this
definition, to facilitate countries in collecting
information necessary to allow accurate inter-
country comparisons.
METHODS
This analysis was conducted using popul ation-based
survey data on gastroenteritis from Australia,
Canada, Ireland, Malta, and the United States.
The original study methodologies are described in
Table 1. In these studies, gastroenteritis refer s to
the acute onset of enteric sympt oms unrelated to
existing health conditions, medication use, or other
known non-infectious causes. The population covered
in the five study areas ranged from 44 million in
the United States to 0
.
38 million in Malta, and the
sample sizes varied from 16 435 (United States) to
3496 (Canada).
Four symptom-based case definitions (FoodNet
[14], Irish [19], National Studies of Acute Gastro-
intestinal Illness (NSAGI) [15], and Norwegian [16])
were selected from the literature to reflect the range of
published definitions from community-based studi es
of gastroenteritis that co uld be applied to existing
population data from the five countries (Table 2).
These definition s were applie d to individual country
data by investigators within that country. For this
analyses, all individuals not meeting the case defi-
nition were included in the non-case group.
We evaluated the impact of each case definition on
observed estimates of incidence per person-year
(overall and by gender), the mean age of cases, the
proportion of cases with gastrointestinal symptoms
(vomiting only, diarrhoea only, both vomiting and
diarrhoea), the proportion of cases with secondary
symptoms (bloody diarr hoea, fever), the mean dur-
ation of illness, and the proportions of cases who saw
a physician, submitted a stool specimen, were hospi-
talized, missed work, and had ongoing symptoms at
time of interview.
The results of these analyses were evaluated to de-
termine if systematic differences in definitions existed
that would enable the development of case definition
multipliers’. We hypothesized that if such systematic
variation existed between case definitions (e.g. case
definition A was two times greater than case definition
B), multipliers could be used to relate the incidence
estimates from studies which used different de fi-
nitions.
The results of this investigation were used to de-
velop a recommended standard case definition and
recommended set of results to be reported. A draft
standard definition, designed for simplicity and broad
utility, was presented at the third Annual Meeting of
the International Collaboration on Enteric Disease
A common, symptom-bas ed case definition for gastroenteritis 887
Table 1. Original methodologies of the five population-based studies of gastroenteritis whose data were used in this analysis
Australia Canada Ireland Malta United States
Sample size 6087 3496 9903 3504 16 435
Cooperation rate 68 % 35 % 84 % 100% 33 %
Study area population 19 million 0
.
5 million 5 million 0
.
38 million 44 million
Study methodology Telephone, cross-
sectional, retrospective
Telephone cross-sectional,
retrospective
Telephone, cross-sectional,
retrospective
Telephone, cross-sectional,
retrospective
Telephone, cross-sectional,
retrospective
Study period Sep. 2001–Aug. 2002 Feb. 2001–Feb. 2002 Dec. 2000–Nov. 2001 Apr. 2004–Dec. 2005 Mar. 2002–Feb. 2003
Study area Australia Population of one municipality Ireland and Northern Ireland Population of Malta and Gozo Selected counties in the USA
Sampling method household Random digit dialling Randomly selected telephone
numbers
Random digit dialling Random sample of individuals
identified and contacted
(telephone or mail)
Random digit dialling
Sampling method individual
within the household
Chosen by last birthday Chosen by next birthday Chosen by next birthday Kish Grid
Sampling frame All persons resident in private
households with a fixed line
telephone
All persons resident in private
households listed in the
electronic directory
All persons resident in private
households with a fixed line
telephone
All persons resident in Malta,
from the general population
database
All persons resident in private
households with a landline
telephone
Language (in which interview
conducted)
Arabic, Cantonese, English,
Greek, Italian, Vietnamese,
Mandarin
English English Maltese, English English, Spanish
Timing of interviews Daytime/evenings/weekends Daytime/evenings/weekends Evenings/weekends Daytime/evenings Daytime/evenings/weekends
Contact attempts Up to 10 Up to 5 Up to 4 Up to 10 Up to 20
Variables used in statistical
weighting
Area (i.e. state/territory), age,
sex, household size, number
of telephone lines in each
household
None Age, sex, jurisdiction Age, sex Age, sex, household size,
number of telephone lines
Illness term Acute gastroenteritis Acute gastrointestinal illness Acute gastroenteritis Infectious intestinal disease Diarrhoeal illness
Time period for observation 4 weeks prior to interview 4 weeks prior to interview 4 weeks prior to interview 4 weeks prior to interview 4 weeks prior to interview
Case definition inclusion
criteria
o3Doro2V;oro4Dor
o3 V when symptoms of
respiratory illness are also
present in 24 h
D, or V o3 D; or bloody D ; or V with
one of D, cramps/abdominal
pain, fever in 24 h
o3Doro3 V in 24 h period ;
or D or V with o2
additional symptoms
(abdominal cramps,
abdominal pain, fever,
nausea, blood in stool,
mucus in stool, diarrhoea
or vomiting)
o3 D in 24 h lasting >1 day
or resulting in activity
restriction
Case definition exclusion
criteria
Non-infectious causes (e.g
pregnancy, medications,
chronic illness, or alcohol
consumption)
Chronic causes of D or V (e.g.
morning sickness, Crohn’s
disease, ulcerative colitis)
Non-infectious causes of D or
V, including excess alcohol,
morning sickness, Crohn’s
disease, and ulcerative colitis
Pre-existing illness or non-
infectious conditions in
which vomiting/diarrhoea is
a symptom or the concurrent
taking of any medications
which can cause diarrhoea/
vomiting as side-effects
Chronic cases of D (e.g. colitis,
IBS), or surgical removal of
part of stomach or intestines
Reference [17] [15] [19] [21, 22] [18]
D, Diarrhoea (i.e. loose stool) ; V, vomiting IBS, irritable bowel syndrome.
888 S. E. Majowicz and others
Burden of Illness Studies (18 March, 2006, Atlanta,
GA, USA). At that time, the Collaboration had rep-
resentation from over 20 countries involved in con-
ducting or planning burden-of-illness studies, of
which population-based surveys of gastroenteritis
form a main component [25]. The expert feedback
obtained from this group informed the final standard
case definition and minimum set of results to be re-
ported. This definition was then applied to the data
from the five countries participating in this analysis.
Analyses wer e conducted in Microsoft Excel 2000
(Microsoft Corporation, Redmond, WA, USA),
SPSS versions 12.0 and 14.0 for Windows (SPSS Inc.,
Chicago, IL, USA), SAS version 9.1 (SAS Institut e,
Cary, NC, USA), and Intercooled Stata version 8
(Stata Corp, College Station, TX, USA).
RESULTS
The impact of using different case definitions
Under the four selected symptom-based case defi-
nitions (FoodNet, Irish, NSAGI, and Norwegian),
the observed incidence per person-year for each of the
five countries ranged as follows (Fig. 1) : Australia
[0
.
58 (95% CI 0
.
47–0
.
70) to 1
.
21 (95% CI
1
.
06–1
.
35)]; Canada [0
.
85 (95 % CI 0
.
75–0
.
97) to 1
.
3
(95% CI 1
.
1–1
.
4)]; Ireland [0
.
43 (95% CI 0
.
38–0
.
63)
to 0
.
75 (95% CI 0
.
690
.
81)]; Malta [0
.
21 (95% CI
0
.
19–1
.
90) to 0
.
37 (95 % CI 0
.
35–1
.
89)] and the
United States [0
.
59 (95 % CI 0
.
55–0
.
64) to 1
.
03 (95 %
CI 0
.
97–1
.
09)]. Under the FoodNet definition, the
incidence of gastroenteritis in Canada was signifi-
cantly higher than in Australia, Ireland, and the
United States, and the incidence in the United States
was significantly higher than in Ireland. Under both
the Irish and Norwegian definitions, the incidence of
gastroenteritis in Australia, Canada, and the United
States were not significantly different from each other,
but were all significantly greater than the incidence in
Ireland. Under the NSAGI definition, the incidence of
Table 2. Published symptom-based case definitions for gastroenteritis applied in this analysis to population data
from Australia, Canada, Ireland, Malta, and the United States
Definition
name Illness
Time period for
observation Definition Exclusions Ref.
FoodNet Diarrhoeal
illness
4 weeks prior
to interview
o3 D in 24 h
lasting >1 day, or
resulting in activity
restriction
Chronic cases of D (e.g. colitis,
irritable bowel syndrome),
or surgical removal of
part of stomach or intestines
[14]
Irish Acute
gastroenteritis
4 weeks prior
to interview
o3 D; or bloody D ;
or V with one of D,
cramps/abdominal
pain, fever in 24 h
Non-infectious causes of D or V,
including excess alcohol,
morning sickness, Crohn’s disease,
and ulcerative colitis
[19]
NSAGI Acute
gastrointestinal
illness
4 weeks prior
to interview
D or V Chronic causes of D or V (e.g.
morning sickness, Crohn’s
disease, ulcerative colitis)
[15]
Norwegian Gastroenteritis 4 weeks prior to
interview
o3 D in 24 h; or at least
3 of the following: V,
nausea, abdominal
cramps, fever
Chronic diarrhoeal illness [16]
FoodNet, United States Foodborne Diseases Active Surveillance Network ; NSAGI, National Studies on Acute
Gastrointestinal Illness ; D, diarrhoea (i.e. loose stool); V, vomiting.
0·00
0·20
0·40
0·60
0·80
1·00
1·20
1·40
FoodNet Irish NSAGI Norwegian
Case definition applied
Incidence per person-year
Fig. 1. Observed incidence per person-year, under the four
selected symptom-based case definitions for gastroenteritis,
in Australia (–r–), Canada (–^–), Ireland (–¾–), Malta
(–+–), and the United States (–%–). NSAGI, National
Studies of Acute Gastrointestinal Illness.
A common, symptom-bas ed case definition for gastroenteritis 889
gastroenteritis in Australia, Canada , and the United
States were all significantly greater than the incidence
in Ireland, and the incidence in Canada was signifi-
cantly greater than the incidence in the United State s.
Under all definitions, the incidence of gastroenteritis
in Malta was not significantly different than the inci-
dence in any of the other countries.
Although the use of different definitions impacted
the incidence per person-year in males and females,
the relative incidence varied little, with females con-
sistently having a higher incidence than males under
all definitions across all countries. Under the different
definitions, the incidence in women was 1
.
3–1
.
4 times
higher than the incidence in men in Australia, 1
.
2–1
.
4
times higher in Canada, 1
.
6–1
.
7 times higher in
Ireland, 1
.
3–1
.
5 tim es higher in Malta, and 1
.
2–1
.
3
times higher in the United States. The mean age
of cases observed varied under the four definitions,
although the difference was always <5 years.
The proportion of cases with bloody diarrhoea is
shown in Figure 2. The observed proportion of
cases with bloody diarrhoea was highest under
the FoodNet definition for Australia, Malta, and the
United States, under the Irish definition for Canada,
and under the Norwegian definition for Ireland. The
observed proportion of cases with fever varied by
definition and country, and was highest under the
Irish definition (Australia and the United States),
the Norw egian definition (Canada and Ireland), and
the FoodNet definition (Malta).
The proportion of cases who visited a physician for
their illness varied by case definition (Fig. 3), with
the highest proportion of cases seeking medical care
observed under the FoodNet definition (Australia,
Canada, and Malta), and equally high under the
Irish and Norwegian definitions (Ireland and the
United States). The proportion visiting a physician in
Australia, Canada, and the United States were similar
under the Irish, NSAGI, and Norwegian definitions.
The proportion of cases who submitted a stool sample
(Fig. 4) was highest under the FoodNet defin ition
(Australia, Canada, and Ireland), the Irish definition
(United States), and equally high under the Irish,
NSAGI and Norwegian definitions (Malta). Except in
Malta, this proportion was consistently lowest under
the NSAGI definition for all countries.
The mean duration of illness varied by about half
a day, and ranged from 2
.
4to3
.
2 days (Australia),
4
.
2–4
.
8 days (Canada), 4
.
2–4
.
3 days (Malta), and
3
.
3–3
.
6 days (United States). However, the mean
duration of illness was 2 days in Ireland under all
of the four different definitions. The observed pro-
portion of cases whose symptoms were still ongoing at
the time of interview ranged just under 2 % in Malta
(18
.
2–20
.
0%) and the United States (10
.
8–11
.
0%),
to just over 3% in Australia (5
.
4–8
.
7%), Canada
(14
.
0–17
.
9%), and Ireland (17
.
3–20
.
7%).
Feasibility of case definition multipliers
The incidence of gastroenteritis was always the lowest
under the FoodNet definition, regardless of country.
In Malta, the incidence under each of the other three
definitions was 1
.
8 times greater than the incidence
under the FoodNet definition. In the other four
0·00
0·05
0·10
0·15
0·20
0·25
0·30
0·35
0·40
0·45
0·50
Case definition a
pp
lied
Proportion of cases who saw a physician
FoodNet
Irish NSAGI Norwegian
Fig. 3. Observed proportion of cases who saw a physician
for their illness, under the four selected symptom-based case
definitions for gastroenteritis, in Australia (–r–), Canada
(–^–), Ireland (–¾–), Malta (–+–), and the United States
(–%–). NSAGI, National Studies of Acute Gastrointestinal
Illness.
0·00
0·01
0·02
0·03
0·04
0·05
0·06
FoodNet
Irish NSAGI Norwegian
Case definition a
pp
lied
Proportion of cases with bloody diarrhoea
Fig. 2. Observed proportion of cases with bloody diarrhoea,
under the four selected symptom-based case definitions for
gastroenteritis, in Australia (–r–), Canada (–^–), Ireland
(–¾–), Malta (–+–), and the United States (–%–). NSAGI,
National Studies of Acute Gastrointestinal Illness.
890 S. E. Majowicz and others
countries, the incidence of gastroenteritis was highest
under the NSAGI definition, and was 1
.
5 (Canada),
1
.
7 (Ireland, United States), and 2
.
1 (Australia) times
higher than the incidence observed under the
FoodNet definition. Under the Irish and Norwegian
definitions the patterns were less clear. In Canada,
the incidence under these two definitions was 1
.
1
times greater than the incidence under the FoodNet
definition. The ratio to the FoodNet definition was
greater for the Norw egian definition vs. the Irish
definition in Australia (1
.
7 vs.1
.
6) and the United
States (1
.
6 vs.1
.
3). However, the ratio to the FoodNet
definition was less for the Norwegian definition vs.
the Irish definition in Ireland (1
.
1 vs.1
.
3).
Recommended standard case definition and minimum
set of results
The following standard symptom-based case defi-
nition for gastroenteritis was chosen : a case of gas-
troenteritis is an individual with o3 loose stools, or
any vomiting, in 24 h, but excluding those (a) with
cancer of the bowel, irritable bowel syndrome,
Crohn’s disease, ulcerative colitis, cystic fibriosis,
coeliac disease, or another chronic illness with symp-
toms of diarrhoea or vomiting, or (b) who report
their symptoms were due to drugs, alcohol, or preg-
nancy. This case definition can be used with any time
period for obs ervation (e.g. in the 4 weeks prior to
the interview). This definition was chosen for its
simplicity, accepta bility and mid-range severity of
symptoms: these elements are particu larly impor tant
when considering the range of countries that have an
interest in the burden of gastroenteritis, including
both developed and developing countries.
Applying the standard definition to data from
Australia, Canada, Ireland, Malta, and the United
States (Table 3) illustrated that the incidence of gas-
troenteritis was highest in Australia, Canada, and
the United States (where the incidences were not sig-
nificantly different), followed by Ireland. Although
Malta had the lowest incidence, it was not signifi-
cantly different than the incidence in any of the other
countries.
DISCUSSION
Using different sympt om-based case definitions for
gastroenteritis impacts the observed epidemiology
of disease in a given population. The four different
case definitions applied produced different incidence
estimates within a given country, suggesting that the
direct comparison of such estimates between studies
with different case definitions may not be valid.
Additionally, the comparison of results that rely
on estimates of incide nce or the number of cases, for
example burden and cost estimates, may not be valid
unless it accounts for variation due to case definition.
This is important, not only when comparing results
between studies, but also when generating global
burden-of-disease estimates.
Unfortunately, this analysis did not include data or
evaluate case definitions from studies conducted in
developing countries, as such information was un-
available at the time. Thus, the repetition of this
analysis in futur e using informatio n from developing
countries is merited. Moreover, given that the epi-
demiology of gastroenteritis probably differs between
developing and developed countries, future analyses
should evaluate how different case definitions (in-
cluding the standard definition presented here) impact
the observed incidence and distribution of gastro-
enteritis in developi ng countries in relation to devel-
oped countries.
An objective of this study was to assess the feasi-
bility of developing case definition multipliers
which could be used to adjust for variation between
incidence rates generated under different definitions.
We considered the results from five countries too
limited to generate specific multipliers between all
four definitions, but they do suggest that liberal defi-
nitions, like the NSAGI definition (loose stool or
vomiting) generate incidence estimates about 1
.
5–2
0·00
0·01
0·01
0·02
0·02
0·03
0·03
0·04
0·04
0·05
0·05
Case definition applied
Proportion of cases who submitted
a stool sample
FoodNet Irish NSAGI Norwegian
Fig. 4. Observed proportion of all cases who submitted a
stool specimen, under the four selected symptom-based case
definitions for gastroenteritis, in Australia (–r–), Canada
(–^–), Ireland (–¾–), Malta (–+–), and the United States
(–%–). NSAGI, National Studies of Acute Gastrointestinal
Illness.
A common, symptom-bas ed case definition for gastroenteritis 891
times greater than incidence estimates generated
by stricter definitions, such as the FoodN et definition
(o3 loose stools in 24 h, lasting >1 day or resulting
in activity restrict ion). Further assessment is needed,
ideally involving data from all countries that
have conducted population-based studies of gastro-
enteritis, to definitively determine whether universal
multipliers exist between specific definitions. The
validity of specific country estimates should also be
subjected to evaluation against methodologies such
as serological surveys.
Interestingly, although the use of different defi-
nitions produced different gender-specific incidence
values and age distributions, the overall conclusions
were not impacted significantly since higher rates in
women than men were always observed, and the mean
age of cases varied by < 5 years. However, it should
be noted that eventual inclusion of studies from de-
veloping countries may result in wider variation.
The choice of sympt om-based case definition im-
pacted the observed clinical picture of illness. As
expected, stricter definitions tended to generate higher
observed proportions of cases with bloody diarrhoea
or fever, although the overall magnitude of the change
under the different definitions was small. However, if
such data are used to determine symptom-specific
burden-of-illness estimates, such as the burden and
cost due to bloody diarrhoea, the potential for such
estimates to be affected by the chosen case definition
should be stated. The observed duration of illness
varied under the different definitions, albeit by <1
day. However, this level of variation is still important
since variation of 1 day against a mean duration of 4
days will impact burden estimates by 20%. Thus, as
above, comparisons of durations be tween studies, or
of results that rely on duration-of-illness estimates,
should acknowledge the potential that such estimates
are affected by the case definition chosen. Lastly, the
proportion of cases seeking medic al care and submit-
ting stool samples for testing was impacted by the
choice of case defi nition, suggesting that under-
reporting estimates derived from these values may not
be directly comparable across studies using different
case definitions.
In light of the results of this study, we recommend
the following standard, sympto m-based case defi-
nition: a case of gastroenteritis is defined as an
individual with o3 loose stools, or any vomiting,
in 24 h, but excluding those (a) with cancer of
the bowel, irritable bowel syndrome, Crohn’s disease,
ulcerative colitis, cystic fibriosis, coeliac disease, or
another chronic illness with symptoms of diarrhoea
or vomiting, or (b) who report their symptoms were
due to drugs, alcohol, or pregnancy. Furthermore, we
Table 3. Epidemiology of gastroenteritis under the standard case definition (o3 loose stools, or any vomiting, in
24 h, excluding* those (a) with cancer of the bowel, irritable bowel syndro me, Crohn’s disease, ulcerative colitis,
cystic fibriosis, coeliac disea se, or another chronic illness with symptoms of diarrhoea or vomiting, or (b) who report
their symptoms were due to drugs, alcohol, or pregnancy) in Australia, Canada, Ireland, Malta, and the United
States
Result Australia Canada Ireland Malta United States
Incidence per person-year 1
.
00 0
.
91 0
.
64 0
.
37 0
.
83
(95% CI) (0
.
88–1
.
10) (0
.
80–1
.
02) (0
.
590
.
70) (0
.
36–1
.
89) (0
.
78–0
.
89)
Incidence per person-year in males 0
.
87 0
.
78 0
.
51 0
.
31 0
.
78
Incidence per person-year in females 1
.
07 1
.
00 0
.
77 0
.
44 0
.
80
Mean age of cases (years) 31
.
86 35
.
97 24
.
18 34
.
82 28
.
44
Mean duration of illness (days)# 2
.
39 4
.
24 2
.
93 4
.
24 3
.
12
Cases with bloody diarrhea (%) 0
.
87 3
.
18 0
.
90 5
.
10 2
.
34
Cases who saw physician (%) 21
.
84 21
.
03 25
.
50 39
.
40 18
.
12
Cases submitting a stool sample for testing (%) 2
.
78 3
.
18 1
.
80 2
.
00 2
.
93
Cases with respiratory symptoms (%)$ 29
.
93 48
.
41 19
.
20 47
.
83
Cases with symptoms still ongoing
at time of interview (%)·
8
.
22 13
.
10 16
.
90 18
.
20 10
.
25
* Individuals meeting the exclusion criteria were retained in the non-case group.
# Mean duration calculated by averaging the duration of illness for all cases, regardless of whether they were still ongoing
at the time of data collection.
$ Coughing, sneezing, sore throat, runny nose.
· For retrospective studies.
892 S. E. Majowicz and others
recommend that the results given in Table 3 be a
minimum set of reported results, to facilitate accurate
inter-country comparisons and global burden-of-
disease estimates. We recognize that the definition is
based, in part, on pragmatism, in that it was not
chosen solel y to improve the accuracy of case class-
ification but also for its simplicity and broad appli-
cability. However, the benefit gained by the removal
of the variation due to case definition when com-
paring results between studies justifies its adoption
and use, and we advocate that future population-
based studies of gastroenteritis structure data collec-
tion so that this standard definition can be applied
and the minimum set of results under this definition
be reported.
The recommended standard case definition can be
used with any time period for observation (e.g. the 4
weeks preceding the interview), however, the potential
for recall bias to impact the results must be con-
sidered. Although recall bias is a recognized issue
in retr ospective surveys of gastroenteritis [10], there
are no published studies which determine the most
appropriate observat ion period to minimize recall
bias in retrospective studies of gastroenteritis. To date,
the majority of retrospective studies use an obser-
vation period of the 4 weeks preceding the interview
[14–19, 21, 22], and future studies may choose to use
this same period to maintain consistency. However,
determining which observation period minimizes
recall bias is a critical methodological issue that
should be addressed in future.
In and of themselves, the minimum sets of results
reported here for the five countries should not be used
directly. Rather, the results reported in the original
studies should be taken as the estimates of the epi-
demiology of gastrointestinal illness in the study
populations [15, 17–19, 21, 22]. These standard ized
values, which provide a more accurate way of com-
paring results between studies, should be used to
compare the epidemiology of gastroenteritis between
Australia, Canada, Ireland, Malta, and the United
States.
It is important to note that, while having a standard
case definition improves the comparabi lity of results
between population-based studies of gastroenteritis,
other methodological issues potentially affecting
comparability exist, which should be addressed in
future. For example, several studies have evaluated
aspects of the relationship between respiratory symp-
toms and gastrointestinal symptoms in cases of gas-
troenteritis [6, 9, 17], under the rationale that when
studies aim to estimate gastroenteritis, resear chers
should attempt to exclude those whose gastrointesti-
nal symptoms are due to respiratory infection. Since
these studies do not provide conclusive guidance on
such exclusion criteria, no attempt was made here to
exclude cases on the basis of respiratory symptoms.
However, as reflected in the minimum set of results to
be reported, we suggest that population-based studies
of gastroenteritis should collect information on
whether cases also experienced respiratory symptoms
(sore throat, runny nose, coughing, sneezing) and
report this proportion, so that as the appropriate
exclusion criteri a are developed, individuals can be
excluded accordingly.
Aside from case definition considerations, other
methodological issue s which may impact compar-
ability between studies pertain to study design and
data analysis. Study design considerations include
determining the most appropriate time period for
observation in retrospective studies, evaluating how
the results from retrospective and prospective studies
relate, and defining an appropriate symptom-free
period prior to illness. Analytical considerations in-
clude appropriate methods for calculating duration of
illness in retrospective studies. Difficulties arise when
calculating the mean duration for two reasons . For
those who are still suffering symptoms, the reported
duration will underestimate the total duration of ill-
ness because the episode of illness is not yet complete ;
this is usually addressed using survival analysis, as
some of the data are censored. However, individuals
with longer durations of illness are more likely to
be included as cases in retrospective surveys than
individuals with shorter durations ; this bias arises
from the same process that gives rise to length bias in
screening programmes, and its impact has not yet
been evaluated. Further exploration of these various
factors is needed.
CONCLUSIONS
In a given country, using different symptom-based
case definitions for gastroenteritis affects its observed
epidemiology, with diff erent definitions yielding
different estimates of the incidence, as well as moder-
ately different clinical pictures of disease. To facilitate
accurate inter-country comparisons of population-
based studies of gastroenteritis, diarrhoeal disease,
and enteric disease, we recommend a common symp-
tom-based case definition, as well as a minimum set
of results to be reported under this definition. We
A common, symptom-bas ed case definition for gastroenteritis 893
advocate that this definition and its set of results be
reported alongside any other study-specific definitions
in future population-based studies, that this analysis
be repeated with data from developi ng countries, and
that countries with existing population-based data
apply this definition in a re-analysis of their results.
Removing the variation due to differences in case
definition will also contribute to developing credible
estimates of the global burden of gastroenteritis.
ACKNOWLEDGEMENTS
The authors thank the International Collaboration
on Enteric Disease Burden of Illness Studies for
providing feedback on the overall concept, and
for reviewing drafts of the standar d definition; in
particular, the authors thank Frederick Angulo and
Martyn Kirk.
DECLARATION OF INTEREST
None.
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894 S. E. Majowicz and others
    • "" Foodborne " indicates the mode of transmission, so definitions of FBD might vary depending on the targets of surveillance programs/projects. Two common definitions used in surveillance programs are the World Health Organization's (WHO) definition, " a disease of an infectious or toxic nature caused by or thought to be caused by the consumption of food or water, " (Schmidt and Gervelmeyer, 2003) and a symptom-based case definition for gastroenteritis, " a case of gastroenteritis is an individual with ≥ 3 loose stools, or any vomiting, in 24 h, " (Majowicz et al., 2008) although FBD may include other diseases than gastroenteritis (Flint et al., 2005). FBD outbreaks are defined as " two or more people who got gastrointestinal disorder after eating the same meal " (Lynch, Painter, Woodruff, and Braden, 2006; Olsen, MacKinnon, Goulding, Bean, and Slutsker, 2000; WHO, 2008). "
    [Show abstract] [Hide abstract] ABSTRACT: Foodborne diseases (FBD), with their varied clinical characteristics and causes, are a global public health concern. The World Health Organization (WHO) estimates that one billion people in developing countries and one-third of the population in developed countries are affected by FBD annually, resulting in significant economic losses. In Vietnam, approximately 200 foodborne outbreaks, 6,000 cases, and 50 deaths are reported annually. The majority of detected foodborne outbreaks have been linked to large canteens, while almost all fatal cases were associated with family meals. Public health statutory surveillance systems rely on outbreak investigation reports, and most outbreaks are only detected when severe cases are admitted to health facilities or when deaths occur. It is therefore clear that these figures are an underestimate, which implicates FBD as a significant public health and economic burden in Vietnam. In developing countries, public health systems face many challenges in ensuring food safety, including shortages of human resources, laboratory capacities, and financial resources. These shortcomings result in poor surveillance and response systems, which are not able to accurately estimate the burden of FBD, trends, contributing factors, and source attribution. Principles of food safety and best practices of food production are critical for comprehensive FBD prevention and control. However, capacity to monitor the complete food production chain is limited and outside the jurisdiction of public health. Therefore, studies in this dissertation focus on improving surveillance and response systems for food safety. The five studies (I to V) in this dissertation describe and evaluate the public health surveillance systems and responses to various foodborne outbreaks in Southern Vietnam from 2009 to 2013. Studies I to IV aim to identify the vehicles, sources, causative agents, and risk factors associated with the outbreak. These studies use various analytic methods to identify gaps and shortcomings in the surveillance and investigation of foodborne outbreaks. Study V then evaluates food-handlers’ food safety knowledge, attitudes, and practices at large canteens. The main findings of these studies help to identify feasible approaches to build capacity and improve public health practices in resource-poor settings. We identified likely outbreak vehicles and sources in four outbreak investigations, although we were unable to identify causative agents in Studies I and III. We identified risk factors contributing to these outbreaks, particularly the inadequate personal hygiene and food hygiene practices of food-handlers. Additionally, findings of outbreak investigations showed that only severe cases sought care at hospitals, clinicians alerted public health officials to suspected outbreaks, and these notifications were usually delayed. The notifiable disease system, operated by Southern Vietnam Preventive Medicine Centers, failed to detect clusters of cases or suspected foodborne outbreaks; it was also rare that surveillance data were analyzed and disseminated to Vietnam Food Safety Agencies (FSAs). Foodborne notification/complaint systems were not set up to receive FBD complaints from the public. Currently, only outbreak investigation reports are used to track food safety, but these reports usually contain only limited information and state few contributing factors and recommendations. Almost all public health/preventive medicine personnel in Southern Vietnam were trained to conduct outbreak investigations, but standard epidemiologic methods were not appropriately applied. For example, no standard case definitions and questionnaires were developed for conducting outbreak investigations. Most case information that food safety authorities reported was transcribed from hospital records. Investigators did not request or obtain any specimens from patients; conclusions regarding the causes of outbreaks were mainly based on results of laboratory tests of food samples. Food-preparation site investigations yielded inadequate information. No flow charts of food operations were drawn and no interviews with food-handlers were conducted, and stool samples of food-handlers and environmental samples were not taken as required. Although most FSAs had limited capacity to perform foodborne outbreak investigations, they rarely requested technical support from the central level. Most microorganism and physico-chemical testing in water and foods were conducted in laboratories at the central level. In Study V, we conducted a cross-sectional survey on food safety knowledge, attitudes, and practices (KAP) and on the training needs of food-handlers in large canteens. Of the 909 food-handlers participating in the study, knowledge, attitudes, and practices were considered adequate for 26%, 36%, and 26%, respectively. After controlling for potential confounders in logistic regression models, the number of food-handlers reporting adequate KAP in schools was about twice as high as the number of such food-handlers in factories. Food-handlers’ suggestions for training needs included appropriate location of the training venue at the workplace, involvement of managers, fewer trainees per course, more practical exercises, and longer course duration. In these studies, we found that public health surveillance systems for food safety are mainly based on foodborne outbreak investigations, response capacities to foodborne outbreaks are limited, and food-handlers’ KAP are poor. We therefore recommend the following: i) For public health surveillance and response in resource-poor settings, food safety authorities and policy-makers should consider including syndromic surveillance in food safety systems, based on existing notifiable disease reporting for infectious diseases. Notification/complaint systems should be available to receive calls from the public. ii) The Vietnam Field Epidemiology Training Program of the Ministry of Health, in collaboration with the Ministry of Agriculture and Rural Development, should develop a strategy and plan to train outbreak response teams at all administrative levels, in order to reach the target of making at least one trained field epidemiologist available per 200,000 people. iii) Efforts to educate food-handlers, together with supportive supervision conducted by managers, have great potential to improve food-handlers’ KAP, especially among those working in factories. iv) We recommend that further studies investigate contributing factors in food preparation and foodborne outbreaks, the burden of foodborne diseases, and source attribution.
    Full-text · Thesis · Jan 2016 · PLoS ONE
    • "An individual was classified as having diarrhea if the primary respondent reported (for himself or another member of the household) any occurrence of watery and/or soft diarrhea in the seven days preceding the survey while those classified as having vomiting reported any vomiting in the seven days preceding the survey. In addition, we adopted a case definition of acute gastroenteritis (AGI) recommended by Majowicz et al. [21] with some modifications due to limited clinical details. In our study we define a case of AGI as an individual with three or more loose stools or any vomiting in 24 h, but excluding those with irritable bowel syndrome, Crohn's disease, ulcerative colitis, celiac disease, or another condition with symptoms of diarrhea or vomiting such as pregnancy. "
    [Show abstract] [Hide abstract] ABSTRACT: Background: Community water supplies in underserved areas of the United States may be associated with increased microbiological contamination and risk of gastrointestinal disease. Microbial and health risks affecting such systems have not been systematically characterized outside outbreak investigations. The objective of the study was to evaluate associations between self-reported gastrointestinal illnesses (GII) and household-level water supply characteristics. Methods: We conducted a cross-sectional study of water quality, water supply characteristics, and GII in 906 households served by 14 small and medium-sized community water supplies in Alabama's underserved Black Belt region. Results: We identified associations between respondent-reported water supply interruption and any symptoms of GII (adjusted odds ratio (aOR): 3.01, 95% confidence interval (CI) = 1.65-5.49), as well as low water pressure and any symptoms of GII (aOR: 4.51, 95% CI = 2.55-7.97). We also identified associations between measured water quality such as lack of total chlorine and any symptoms of GII (aOR: 5.73, 95% CI = 1.09-30.1), and detection of E. coli in water samples and increased reports of vomiting (aOR: 5.01, 95% CI = 1.62-15.52) or diarrhea (aOR: 7.75, 95% CI = 2.06-29.15). Conclusions: Increased self-reported GII was associated with key water system characteristics as measured at the point of sampling in a cross-sectional study of small and medium water systems in rural Alabama in 2012 suggesting that these water supplies can contribute to endemic gastro-intestinal disease risks. Future studies should focus on further characterizing and managing microbial risks in systems facing similar challenges.
    Full-text · Article · Jan 2016
    • "In five recently completed telephone surveys conducted across European Union Member States, self-reported illness rates ranged from 1.4 cases per person per year in Denmark to 0.33 cases per person per year in France56789 . However, comparing international rates is hampered by disparities in case definitions , study designs, periods of recall of symptoms and the characteristics of the populations studied [10,11]. Most people with IID do not seek medical attention [2,4], and even when they do their illness is often not investigated or reported [12] , so it is difficult to determine accurately the population incidence of disease based on national surveillance or other routinely collected data. "
    [Show abstract] [Hide abstract] ABSTRACT: To estimate the burden of intestinal infectious disease (IID) in the UK and determine whether disease burden estimations using a retrospective study design differ from those using a prospective study design. A retrospective telephone survey undertaken in each of the four countries comprising the United Kingdom. Participants were randomly asked about illness either in the past 7 or 28 days. 14,813 individuals for all of whom we had a legible recording of their agreement to participate. Self-reported IID, defined as loose stools or clinically significant vomiting lasting less than two weeks, in the absence of a known non-infectious cause. The rate of self-reported IID varied substantially depending on whether asked for illness in the previous 7 or 28 days. After standardising for age and sex, and adjusting for the number of interviews completed each month and the relative size of each UK country, the estimated rate of IID in the 7-day recall group was 1,530 cases per 1,000 person-years (95% CI: 1135-2113), while in the 28-day recall group it was 533 cases per 1,000 person-years (95% CI: 377-778). There was no significant variation in rates between the four countries. Rates in this study were also higher than in a related prospective study undertaken at the same time. The estimated burden of disease from IID varied dramatically depending on study design. Retrospective studies of IID give higher estimates of disease burden than prospective studies. Of retrospective studies longer recall periods give lower estimated rates than studies with short recall periods. Caution needs to be exercised when comparing studies of self-reported IID as small changes in study design or case definition can markedly affect estimated rates.
    Full-text · Article · Jan 2016
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