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
     Unit of Epidemiology, Scientific Institute of Public Health,
Brussels, Belgium.
                                                                                schools B–E occurred at different times.
     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:
                                                                                  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

Belgian 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, 2002
142     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, 2002
Belgian 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, 2002
144    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%
   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, 2002
Belgian 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 out
146    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, 2002
Belgian 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. (
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-
have been an overestimation of a low mental health score                      bon dioxide for quality control. Fort Lauderdale, FL:
                                                                              International Society of Beverage Technologists, 1997.
among cases. Finally, extensive media coverage of the inci-              8.   Radford-Knoery J, Cutter G. Biogeochemistry of dissolved
dent in school A could have introduced an information bias                    hydrogen sulfide species and carbonyl sulfide in the western
and resulted in overidentification of cases in schools B–E.                   North Atlantic Ocean. Geochimica et Cosmochimica Acta
   In conclusion, an association was observed between con-                    1994;58:5421–31.
sumption of regular Coca-Cola and illness in school A.                   9.   Nemery B, Fischler B, Boogaerts M, et al. Dioxins, Coca-
                                                                              Cola, and mass sociogenic illness in Belgium. (Letter). Lancet
Exposure to carbonyl sulfide and hydrogen sulfide could                       1999;354:77.
explain the observed symptoms, particularly in early cases.             10.   Coke adds life, but cannot always explain it. (Editorial).
Nonetheless, classic factors of mass sociogenic illness were                  Lancet 1999;354:173.
present and could explain the majority of the later cases in            11.   Small GW, Borus JF. Outbreak of illness in a school chorus:
                                                                              toxic poisoning or mass hysteria? N Engl J Med 1983;308:
both schools A and B–E.                                                       632–5.
   Some limitations of this investigation were related to               12.   Boss LP. Epidemic hysteria: a review of the published litera-
deficiencies in managing the crisis. This problem under-                      ture. Epidemiol Rev 1997;19:233–43.

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scores the need for appropriate independent structures able             13.   Small GW, Feinberg DT, Steinberg D, et al. A sudden outbreak
to analyze readily identified causes and to react quickly.                    of illness suggestive of mass hysteria in schoolchildren. Arch
                                                                              Fam Med 1994;3:711–16.
                                                                        14.   Goh KT. Epidemiological enquiries into a school outbreak of
                                                                              an unusual illness. Int J Epidemiol 1987;16:265–70.
                                                                        15.   Levine RJ. Epidemic faintness and syncope in a school march-
                                                                              ing band. JAMA 1977;238:2373–6.
ACKNOWLEDGMENTS                                                         16.   Cole TB, Chorba TL, Horan JM. Patterns of transmission of
                                                                              epidemic hysteria in a school. Epidemiology 1990;1:212–18.
   The authors acknowledge the directors of the five schools            17.   Jones TF, Craig AS, Hoy D, et al. Mass psychogenic illness
(Bornem, Brugge, Harelbeke, Kortrijk, and Lochristi) for                      attributed to toxic exposure at a high school. N Engl J Med
allowing the investigation to be conducted in the school set-                 2000;342:96–100.
ting and for providing the information on the scenario. They            18.   Philen R, Kilbourne E, McKinley T, et al. Mass sociogenic ill-
                                                                              ness by proxy: parentally reported epidemic in an elementary
also thank the physicians of the hospitals for providing the                  school. Lancet 1989;2:1372–6.
medical information.                                                    19.   Levine RJ, Sexton DJ, Romn FJ, et al. Outbreak of psychoso-
                                                                              matic illness at a rural elementary school. Lancet 1974;2:
                                                                        20.   Smith HC, Eastham EJ. Outbreak of abdominal pain. Lancet
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