Belgian Coca-Cola-related Outbreak: Intoxication, Mass Sociogenic Illness, or Both?
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American Journal of Epidemiology Vol. 155, No. 2
Copyright © 2002 by the Johns Hopkins Bloomberg School of Public Health Printed in U.S.A.
All rights reserved
Belgian Coca-Cola-related Outbreak Gallay et al.
Belgian Coca-Cola-related Outbreak: Intoxication, Mass Sociogenic Illness,
or Both?
A. Gallay,1,2 F. Van Loock,1 S. Demarest,1 J. Van der Heyden,1 B. Jans,1 and H. Van Oyen1
An epidemic of health complaints occurred in five Belgian schools in June 1999. A qualitative investigation
described the scenario. The role of soft drinks was assessed by using a case-control study. Cases were students
complaining of headache, dizziness, nausea, vomiting, abdominal pain, diarrhea, or trembling. Controls were
students present at school on the day of the outbreak but not taken ill. An analysis was performed separately for
school A, where the outbreak started, and was pooled for schools B–E. In school A, the attack rate (13.2%) was
higher than in schools B–E (3.6%, relative risk = 3.6, 95% confidence interval (CI): 2.5, 5.3). Exclusive
consumption of regular Coca-Cola (school A: odds ratio (OR) = 29.7, 95% CI: 1.32, 663.6; schools B–E: OR =
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7.3, 95% CI: 2.9, 18.0) and low mental health score (school A: OR = 16.1, 95% CI: 1.3, 201.9; schools B–E:
OR = 3.1, 95% CI: 1.5, 6.6) were independently associated with the illness. In schools B–E, consumption of
Fanta, consumption of Coca-Cola light, and female gender were also associated with the illness. It seems
reasonable to attribute the first cases of illness in school A to regular Coca-Cola consumption. However, mass
sociogenic illness could explain the majority of the other cases. Am J Epidemiol 2002;155:140–7.
carbonated beverages; disease outbreaks; hydrogen sulfide; poisoning
An epidemic of health complaints, including nausea, vom- schools B–E. In both cases, the company concluded that the
iting, abdominal pain, dizziness, and headache, potentially very low concentration of these two substances could not
related to consumption of Coca-Cola Company soft drinks have caused any toxicity. Still, The Coca-Cola Company
occurred in June 1999 in Belgium. The epidemic started on withdrew 15 million crates of its soft drinks across Belgium,
June 8 in one secondary school (school A). Two to 6 days France, and Luxembourg and temporarily closed three of its
later, students in four other secondary schools (schools B–E) factories in Europe.
complained of the same symptoms. During the same period, On June 23, the Belgian Ministry of Public Health com-
several complaints were reported in the Belgian and the missioned the Unit of Epidemiology of the Scientific Institute
French populations (1, 2). Between June 8 and June 20, the of Public Health (Brussels) to investigate this outbreak and to
Belgian Poisoning Call Centre recorded over 1,400 telephone identify the cause and mode of transmission. Epidemiologic
calls; 55 percent were complaints related to consumption of and clinical information was collected on cases in the affected
Coca-Cola soft drinks, and 45 percent of the callers asked for schools, and a case-control study was performed to determine
information about the quality of the soft drinks (1). The Coca- the weight of evidence on both competing hypotheses—con-
Cola-related calls constituted one third of all calls the sumption of Coca-Cola Company products and mass socio-
Poisoning Call Centre received during this period. genic illness—as a risk factor for illness.
On June 15, The Coca-Cola Company announced that
chemical analysis of the incriminated beverages had MATERIALS AND METHODS
revealed very low concentrations of hydrogen sulfide in the
glass bottles of Coca-Cola supplied to school A, and that 4- It was decided to consider the outbreaks in school A and
chloro-3-methylphenol, applied to transport pallets, had in schools B–E as two distinct incidents because 1) school A
contaminated the exterior surface of the cans delivered to was supplied with glass bottles from an Antwerp (Belgium)
plant, whereas the bottles and cans for schools B–E were
Received for publication February 26, 2001, and accepted for
supplied by plants in Gent (Belgium) and Dunkerque
publication October 12, 2001. (France); 2) The Coca-Cola Company had identified a dif-
Abbreviations: CI, confidence interval; OR, odds ratio; RR, relative ferent toxicologic substance in the soft drinks delivered to
risk. school A and schools B–E; and 3) the events at school A and
1
Unit of Epidemiology, Scientific Institute of Public Health,
Brussels, Belgium.
schools B–E occurred at different times.
2
European Programme for Intervention Epidemiology Training
(EPIET), Brussels, Belgium. Descriptive epidemiology
Reprint requests to Dr. Herman Van Oyen, Unit of Epidemiology,
Scientific Institute of Public Health, J. Wytsmanstraat 16, 1050
Brussels, Belgium (e-mail: herman.vanoyen@iph.fgov.be).
To obtain contextual information regarding the outbreaks,
Coca-Cola, Coca-Cola light, and Fanta are manufactured by The qualitative and open-ended telephone interviews were con-
Coca-Cola Company, Atlanta, Georgia. ducted with the school directors, and a self-administered
140Belgian Coca-Cola-related Outbreak 141
questionnaire was distributed to the physicians in the emer- logistic regression model by using a forward stepwise selec-
gency rooms. Cases were defined as students in school A or tion strategy (SPSS 8.0; SPSS Inc., Chicago, Illinois).
in schools B–E who suffered from at least one of the fol-
lowing complaints on the first day or on the second day after RESULTS
the onset of the outbreak in each school: headache, dizzi-
ness, nausea, vomiting, abdominal pain, diarrhea, or trem- Scenario of the outbreaks
bling. Cases were identified according to a school register of
illnesses filled out by a nurse. Emergency room and hospi- On June 8, 1999, students in school A complained of gas-
tal medical records were then checked for the symptoms and trointestinal symptoms with dizziness and headache shortly
results of physical examinations. Results of biologic and after consuming Coca-Cola from the school restaurant dur-
toxicologic tests of blood and urine samples were collected. ing the midday break. Between 12:30 and 1:00 p.m., three
students reported to the secretarial office with health com-
plaints. At 1:10 p.m., the courses started; by 2:00 p.m., six
Case-control study more students from different classes complained of feeling
ill. Following advice from the medical school inspector, all
Controls were students from the same class as the cases ill students were taken to the local hospital. Of the 33 stu-
and were next on the alphabetic list; these students were pres- dents who went to the emergency unit on June 8, 12 were
ent at school on the first and the following day of the out- hospitalized overnight for observation. Six other students
break and had not been ill during the 2 weeks before the day were taken to the same hospital on June 9. With students
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of the outbreak up to the following day. A 50 percent preva- reporting a “rotten” smell from Coca-Cola bottles, a possi-
lence of exposure to Coca-Cola Company soft drinks among ble link was made with consumption of this beverage. In the
healthy students and a 1:2 ratio of cases to controls were afternoon of June 8, the supplier of Coca-Cola removed
assumed; therefore, a sample size of 49 cases and 98 con- most of the remaining crates from the school.
trols in each school group was required to detect an odds On June 10 (school B), June 11 (school C), and June 14
ratio of 3 or greater with 95 percent confidence and a power (schools D and E), students complained of similar symp-
of 80 percent. toms. In school E, the chief of police ordered all students
Exposure to Coca-Cola Company soft drinks was defined reporting complaints to be sent to the hospital. In school C,
in two different ways. The first definition was consumption a physician came on site to evaluate the situation. On the
of regular Coca-Cola compared with any other consumption basis of the number of students with health complaints, sev-
(other Coca-Cola Company products, non-Coca-Cola eral ambulances and a medical emergency team were sent to
Company products, water, or no consumption at all). the school. In schools B–E, all ill students were transported
According to the second definition, the exposure was exclu- to the local hospital either by ambulance or in staff mem-
sive consumption of a Coca-Cola Company product com- bers’ cars. Following the hotline instructions of The Coca-
pared with water or no consumption at all. Cola Company, the staff of school E had removed all cans
A structured questionnaire was used, and information was stamped on the bottom with specific codes early on the
collected on demographics (gender, age), food consumption morning of June 14 before the courses started. Because of
(place, time) and beverage consumption (place of purchase, extensive media attention given to the outbreak in school A,
place and time of consumption, package, particular taste or the events were assumed to be related to consumption of
smell) on the day of the outbreak, illness among friends, Coca-Cola Company soft drinks.
mental health status, and symptoms (type, time of occur-
rence). A mental health score was calculated according to
responses to the questions on mental health status on the SF- Descriptive epidemiology
36 Health Survey (3). Information was gathered during a In school A, two potential cases did not meet the eligibil-
face-to-face interview in each school between June 25 and ity criteria. The overall attack rate was 13.2 percent. Thirty-
June 27. In one of the B–E schools, students were grouped one students became ill on the first day and six on the fol-
and were assisted by an interviewer when completing the lowing day (figure 1). In schools B–E, 72 cases occurred on
questionnaire. the first day of the outbreaks and three on the following day
(figure 2). The attack rate (3.5 percent) was lower in schools
Analysis B–E than in school A (relative risk (RR) 0.28, 95 percent
confidence interval (CI): 0.19, 0.40; table 1). In addition, the
Crude and gender-specific attack rates in school A and attack rate was higher for girls than for boys in both school
schools B–E were calculated by dividing the number of A (RR 1.8, 95 percent CI: 0.9, 3.6) and schools B–E
cases by the number of students. The mean ages of cases in (RR 5.7, 95 percent CI: 1.8, 17.9). In school A, the cases
school A and schools B–E were compared by using the were younger than those in schools B–E (p < 0.001, table 1).
Kruskal-Wallis test. To compare exposures between cases In school A, with onset of illness occurring before 2:10
and controls, odds ratios and 95 percent confidence intervals p.m.—the first break period after the incident started—the
were computed by using Epi Info software (version 6.04; first nine cases of illness occurred among students in six dif-
Centers for Disease Control and Prevention, Atlanta, ferent classrooms (one to three cases per class); 20 (71.4
Georgia). Exposures found by univariate analysis to be asso- percent) ill students of the remaining 28 cases were grouped
ciated with the illness (p value < 0.2) were included in a in four classrooms (four to six cases per class). In schools
Am J Epidemiol Vol. 155, No. 2, 2002142 Gallay et al.
FIGURE 1. Number of cases of Coca-Cola-related illness, by gender and time of onset of illness, school A, Belgium, 1999. Coca-Cola is man-
ufactured by The Coca-Coca Company, Atlanta, Georgia.
B–E, two thirds (51/75) of the cases were clustered in 11 control per case in school A and fewer than two controls per
classrooms. The number of cases per class ranged from case in schools B–E could be interviewed. In school A, the
three to nine. age and gender of the 37 cases and 34 controls were similar.
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In school A, time of beverage consumption and time of In schools B–E, the 75 cases and 130 controls were similar
onset of symptoms were available for 31 and 37 cases, in age, but cases were more likely to be girls (odds ratio
respectively; in schools B–E, this information was available (OR) 4.3, 95 percent CI: 1.2, 23.6).
for 50 and 75 cases, respectively. In school A, all but three The proportion of students that had bought and consumed
cases drank beverages between 12:00 and 12:30 p.m., with regular Coca-Cola at school was higher among cases than
onset of symptoms 30 minutes to 24.5 hours (median, 3 controls in both school A (OR 36.8, 95 percent CI: 7.8,
hours) later. In schools B–E, the delay between consumption 220.1) and schools B–E (OR 3.5, 95 percent CI: 1.7, 7.0)
of soft drinks and occurrence of symptoms ranged from 30 (table 3). In school A, cases also were more likely to con-
minutes to 7.5 hours (median, 1.5 hours). There was no dif- sume regular Coca-Cola exclusively (OR 23.2, 95 percent
ference in time of onset of symptoms between girls and boys CI: 3.7, 235.5). Exclusive consumption of other beverages
in both schools. (other Coca-Cola and non-Coca-Cola products) was similar
Medical records could be checked for 32 of the 37 cases among cases and controls (table 4). In schools B–E, cases
from school A and for 62 of the 75 cases from schools B–E. were more likely to exclusively consume regular Coca-Cola
Headache, nausea, and dizziness were the main clinical symp- (OR 5.5, 95 percent CI: 2.4, 12.9), Fanta (OR 3.5, 95
toms reported by the first nine cases in school A. Abdominal percent CI: 1.1, 10.9), or Coca-Cola light (OR 12.8, 95
pain, headache, nausea, and respiratory troubles were percent CI: 2.8, 77.9) (table 4). In both school groups, cases
reported more frequently by the later cases. In schools B–E, were more likely to have a low mental health score; the odds
headache, abdominal pain, nausea, and dizziness were the ratio (2.4) was similar in both school groups but was statis-
main clinical symptoms reported on the medical charts (table tically significant for only schools B–E (table 5). In school
2). Physical examination was normal for 27 (84.4 percent) A, cases were more likely to report an off-odor (OR 43.2,
and 56 (90.3 percent) of the patients from school A and 95 percent CI: 8.0, 407.4) or a bad taste (OR 28.0, 95 per-
schools B–E, respectively. Extreme pallor was noted for some cent CI: 3.7, 1,206.7) to the regular Coca-Cola. About one
of the first cases from school A, and flushed skin and/or red third of the cases described the smell as nasty or rotten. In
eyes were noted for six (9.7 percent) students from schools schools B–E, few cases and no controls noted a bad smell,
B–E. All symptoms disappeared spontaneously within several and few cases and one control reported a bad taste. In both
hours for the majority of patients. In each of the school groups school groups A and B–E, having a friend become ill was
A and B–E, 12 students were hospitalized for a period of 1–3 not associated with the disease. Because school A did not
days. Six students from school A and two students from the provide food, the majority of students ate a homemade
other schools relapsed within a couple of days. lunch. In schools B–E, cases were less likely than controls
Although blood and urine samples were collected from to have eaten the food provided by the school (table 5).
students in school A, no results from the routine biologic The following variables were included in the multivari-
and toxicologic analysis could be obtained. The results of a ate model: age; gender; exclusive consumption of bever-
range of routine biologic tests performed on the 56 (74.6 ages (regular Coca-Cola, Fanta, Coca-Cola light, other
percent) blood samples and the seven (9.3 percent) urine soft drinks) as a set of dummy variables, with consump-
samples taken from the 75 students from schools B–E were tion of water or no consumption at all as the reference;
normal. mental health status; the reporting of an off-odor; and the
reporting of a bad taste to soft drinks. In school A, exclu-
Case-control study sive consumption of regular Coca-Cola (OR 29.7, 95
percent CI: 1.32, 663.6) and having a low mental health
Because of practical constraints in schools to interview- score (OR 16.1, 95 percent CI: 1.3, 201.9) remained
ing during the end-of-school examinations, fewer than one independently associated with the illness. In schools B–E,
Am J Epidemiol Vol. 155, No. 2, 2002Belgian Coca-Cola-related Outbreak 143
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FIGURE 2. Number of cases of Coca-Cola-related illness, by gender and time of onset of illness, schools B–E, Belgium, 1999. Coca-Cola is
manufactured by The Coca-Coca Company, Atlanta, Georgia.
exclusive consumption of regular Coca-Cola (OR 7.3, DISCUSSION
95 percent CI: 2.9, 18.0), Fanta (OR 5.8, 95 percent CI:
1.7, 19.5), and Coca-Cola light (OR 15.7, 95 percent CI: The epidemiologic investigation suggested that consump-
3.1, 78.2) remained independently associated with the ill- tion of regular Coca-Cola was a strong determinant of ill-
ness. Girls (OR 4.2, 95 percent CI: 1.0, 16.5) and ness in school A. The short interval between exposure to the
students with a low mental health score (OR 3.1, 95 per- soft drink and occurrence of symptoms favored a toxico-
cent CI: 1.5, 6.6) also were more likely to have reported logic cause (table 6). No other soft drink or food item was
the illness. associated with becoming ill. Regular Coca-Cola was the
Am J Epidemiol Vol. 155, No. 2, 2002144 Gallay et al.
TABLE 1. Descriptive epidemiology of Coca-Cola*-related TABLE 3. Exposure to regular Coca-Cola*,† in school A and
illness, school A and schools B–E, Belgium, 1999 schools B–E, Belgium, 1999
School A Schools B–E Consumption of Cases Controls 95%
OR‡
Attack rate (%) 13.2 (37/280) 3.5 (72/2,060) regular Coca-Cola No. % No. % CI‡
Among girls 15.6 (28/179) 4.3 (72/1,672) School A
Among boys 8.9 (9/101) 0.7 (3/388) Yes 34 91.9 8 23.5 36.8 7.8, 220.1
Relative risk of being No 3 8.1 26 76.5
ill according to Total 37 34
female gender,
by school 1.8 5.7 Schools B–E
(95% CI†: 0.9, 3.6) (95% CI: 1.8, 17.9) Yes 31 41.3 22 16.9 3.5 1.7, 7.0
Age (years) Range, 13–15; Range 13–19; No 44 58.7 108 83.1
median, 13 median, 15 Total 75 130
* Coca-Cola is manufactured by The Coca-Cola Company, * Coca-Cola is manufactured by The Coca-Cola Company,
Atlanta, Georgia. Atlanta, Georgia.
† CI, confidence interval. † Regular Coca-Cola bought and consumed at school on the
day of the outbreak.
‡ OR, odds ratio; CI, confidence interval.
TABLE 2. Symptoms of Coca-Cola*-related illness abstracted
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from the medical records, school A and schools B–E,
Belgium, 1999 TABLE 4. Exclusive exposure to specific beverages* in
school A and schools B–E, Belgium, 1999
School A
Cases Controls 95%
Cases with onset Schools B–E Beverage OR†
(no.) (no.) CI†
Symptom of illness before Later cases (n = 62)
14:10 (first cases) (n = 23) School A (glass bottles)
(n = 9) Regular Coca-Cola 31 8 23.2 3.7, 235.5
Fanta 0 9 0 0, 8.3
No. % No. % No. % Coca-Cola light 0 0
Headache 7 77.8 13 56.5 48 77.4 Other Coca-Cola Company
products 1 3 2.0 0, 50.6
Nausea 6 66.7 7 30.4 36 58.1
Non-Coca-Cola Company
Dizziness 4 44.4 3 13.0 19 30.6 products 0 2 0 0, 47.2
Abdominal Water/no drink 2 12 Reference
pain 3 33.4 15 65.2 39 62.9 Schools B–E (cans and bottles)
Asthenia 2 22.2 5 21.7 0 Regular Coca-Cola 26 20 5.5 2.4, 12.9
Respiratory Fanta 9 11 3.5 1.1, 10.9
Coca-Cola light 9 3 12.8 2.8, 77.9
troubles 1 11.1 7 30.4 3 4.8
Other Coca-Cola Company
Trembling 1 11.1 6 26.0 18 29.0 products 5 5 4.3 0.9, 20.3
Weakness 1 11.1 2 2.7 3 4.8 Non-Coca-Cola Company
Vomiting 0 2 8.7 8 12.9 products 1 5 0.8 0, 8.5
Water/no drink 19 81 Reference
Diarrhea 0 1 4.3 7 11.3
Heart rate * Beverages bought and consumed at school on the day of the
outbreak. Coca-Cola and Fanta are manufactured by The Coca-Cola
≥100 Company, Atlanta, Georgia.
/minute† 3 33.4 2 10.0 5 12.5 † OR, odds ratio, CI, confidence interval.
Fever ≥38˚C‡ 0 1 7.1 3 8.1
* Coca-Cola is manufactured by The Coca-Cola Company,
Atlanta, Georgia.
† Pulse rate was known for the first cases and 20 of the later with the expected symptoms of exposure to carbonyl sulfide
cases in school A and for 40 cases in schools B–E. and hydrogen sulfide (4, 5). Brief exposure to hydrogen sul-
‡ Fever was known for 7 of the first cases and 14 of the later
cases in school A and for 37 cases in schools B–E. fide can be sufficient to induce such symptoms (5, 6). The
first cases may have been exposed to a higher concentration
of carbonyl sulfide and hydrogen sulfide, while the later
cases may have paid attention when opening and drinking
only soft drink that the students characterized as having a the soft drink. It is very unfortunate that, although blood and
rotten smell, typical of carbonyl sulfide and hydrogen sul- urine samples were collected from school A students at the
fide contaminating the carbon dioxide used in the beverage. local hospital, there was no evidence that any analyses were
In the sensory analysis conducted by The Coca-Cola conducted; if there were, the results were unobtainable.
Company’s Northwest Europe Division, a clear off-odor In schools B–E, a similar but weaker association with reg-
was established. The sulfur-containing compound responsi- ular Coca-Cola consumption was observed. Other Coca-
ble for this off-odor was detected in the regular Coca-Cola Cola Company soft drinks (Fanta, Coca-Cola light) were
consumed in school A by gas chromatography in combina- also identified as risk factors. A sensory analysis of the out-
tion with a sniffing technique (GC-SNIFF) (4). Moreover, side of the cans from the production site supplying schools
the main symptoms observed (headache, nausea, and dizzi- B–E detected a “medicine-like” odor, and the GC-MS tech-
ness), particularly among the first cases, were compatible nique (gas chromatography in combination with mass spec-
Am J Epidemiol Vol. 155, No. 2, 2002Belgian Coca-Cola-related Outbreak 145
TABLE 5. Exposure to other risk factors in school A and surface of the cans from the French plant (Dunkerque) (4).
schools B–E, Belgium, 1999 However, in schools B–E, the observed symptoms were not
Cases Controls 95% compatible with the expected symptoms (either eye and skin
Risk factor OR*
(no.) (no.) CI* irritation as a result of dermal contact or severe effects on
School A† mucous membranes caused by ingestion) of the p-chloro-m-
Food provided by school —‡ —‡ cresol exposure (4, 5). None of these symptoms was
Having a friend be ill 36 30 4.8 0.4, 242.8 reported by the students. In addition, all laboratory results
Mental SF-36 Health and physical examinations were normal (table 6).
Survey score§ Bacterial, viral, or parasitologic investigations carried out146 Gallay et al.
Previous papers have attributed, without investigation, the transmitting the outbreak from school to school and from
outbreaks to episodes of mass sociogenic illness (9, 10). In school to the general population (11, 23–25). Moreover, lack
this study, classic risk factors for mass sociogenic illness of transparency about the safety of the Coca-Cola product
were identified in both school groups A and B–E (table 6). and controversial information from officials intensified the
The outbreak was characterized by occurrence among ado- community’s concern. The high awareness and anxiety
lescents or preadolescents in a school setting, a preponder- about the safety of modern food products, combined with a
ance of illness among girls, clustering of cases in classrooms, very strong symbolic image of the incriminated product,
evidence of unusual mental stress among those reporting ill- may have contributed further to the psychosocial distress of
ness, benign morbidity and no clinical or laboratory evidence the general population (1, 2, 22).
of illness, relapse of illness, and rapid spread and dissolution When a possible outbreak of mass sociogenic illness is
of the outbreak (11–15). In both school groups, cases more investigated, a number of difficulties arise in balancing
often than controls had reported a friend being ill on the day competing requirements. These include ensuring, as quickly
of the outbreak (16), although the association was not statis- as possible, that no toxicologic cause exists; identifying the
tically significant. However, it is likely that friends consume existence of an outbreak of mass sociogenic illness; and
similar products or even share them. Similar to several out- communicating the diagnosis in order to stop the spread of
breaks of mass sociogenic illness described previously, a bad the illness. However, because of the lack of pathognomonic
odor of a “gas” was identified by students and could have indicators of mass sociogenic illness and the difficulty in
been a trigger (11–14, 16–19). Jones et al. propose that mass proving the presence of a toxicologic substance, investiga-
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sociogenic illness be considered in any outbreak of acute ill- tions often have become extensive before a diagnosis can be
ness thought to be caused by exposure to a toxic substance stated, which can increase stress (13, 16, 17). Even anxiety
but with minimal physical findings and no environmental can cause real symptoms; if cases are told that their source
cause readily apparent to the investigator (17). Nonetheless, of anxiety is a false belief, this explanation will not reduce
regular Coca-Cola was clearly identified in school A as hav- their embarrassment and can exacerbate their condition
ing a “rotten egg” odor, which is typical of the odor of (26). In this outbreak, interrupting the transmission of symp-
sulfide. This was not usual in previous outbreaks of mass toms by separating exposed groups and suppressing audio-
sociogenic illness in which airborne substances were com- visual transmission seemed practically impossible (16).
monly incriminated with unspecific sources (14, 18–20) or, Because of the great distribution of the soft drinks, and
conversely, many vectors were incriminated (21). In schools because the symbolic image of The Coca-Cola Company is
B–E, the odor described varied. so well known and is highlighted by extensive media cover-
In both school A and schools B–E, belonging to a group age, it would have been difficult to stop the process without
having a low mental health score was independently associ- a quick and complete analysis of the incriminated product
ated with illness and could highlight a stressful situation and clear information about the safety of the soft drink.
being experienced by the ill students. First, the outbreak Such outbreak investigations need transparency, objective
took place during the end-of-school examination period features, and clear information from the different actors
(11). Second, this outbreak occurred within the context of implicated. In the present study, several deficiencies in crisis
the recent Belgian general election and a dioxin crisis in management were identified. For example, the Ministry of
Belgium 2 weeks earlier, which had heightened anxiety in Public Health was already very involved in the dioxin crisis,
the population about food safety (22). The SF-36 Health public measures for withdrawing the implicated products
Survey scores addressed the feelings of the students during were insufficient, and The Coca-Cola Company performed
the previous 4 weeks and provided only an indicator of men- nearly all soft drink analyses. In such a situation, credibility
tal health status. Many students reported that it was difficult of the results and the official information depends on the
to answer this question, because they felt bad since the inci- absence of a conflict of interest.
dent had occurred. Nonetheless, since mental health status The findings of this study are subject to a number of lim-
could easily modify symptom severity or a person’s behav- itations. First, the survey was performed 2 weeks after the
ior, the associations with low mental health scores do not outbreak, during the last week of end-of-school examina-
disprove chemical contamination as a cause of the out- tions, which could have introduced recall errors that partic-
breaks. More complex instruments have been proposed to ularly affected time of beverage consumption and time of
evaluate mass sociogenic illness (14). onset of illness. This information was probably more precise
Under the hypothesis of a mass sociogenic illness, several in school A, where all soft drinks were sold at noon break
features enhanced contagion of the outbreak (table 6). In only. Furthermore, it could be argued that in school A, a
schools B–E, as in many previous outbreaks, the arrival of selection of cases on the exposure may have induced the
ambulances with emergency personnel and the police could association between consumption of regular Coca-Cola and
have increased the general excitement and anxiety, resulting symptoms. This possibility seems highly unlikely. The pro-
in the spread of symptoms (11, 16). In addition, propagation portion of cases that consumed regular Coca-Cola was 100
of the illness accelerated with person-to-person transmission percent among the first nine cases compared with only 87
when students were grouped (during break periods, school percent among cases whose onset of symptoms occurred
lunch) by line-of-sight or audiovisual cues (16). Extensive after the afternoon break between classes. If selection of
nationwide radio and television media coverage of the first cases would have occurred based on the exposure, one
incident in school A probably played a substantial role in would expect the opposite, with the highest proportion of
Am J Epidemiol Vol. 155, No. 2, 2002Belgian Coca-Cola-related Outbreak 147
exposure among the cases identified later, once regular ucts of The Coca-Cola Company, June 1999. Copenhagen,
Coca-Cola was suspected as a cause of symptoms. Factors Denmark: Dansk Toksikologi Center, 1999.
5. Online carbonyl sulphide—HSDB-Hazardous Substances
that contribute to the possible existence and role of mass Data Bank. October 1, 1999. (http://sis.nlm.nih.gov/sis1).
sociogenic illness are difficult to discern. Mental health sta- 6. Goode D. Mass psychogenic illness attributed to toxic exposure
tus at the time was influenced by many factors, not the least at a high school. (Letter). N Engl J Med 2000;342:1673–5.
of which was the end-of-year examinations. There also may 7. Cox J. Determination of carbonyl sulfide concentration in car-
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