Botulism in Argentina

STUDENT’S VERSION

Original investigators: Rodrigo G. Villar, MD,1 Roger L. Shapiro, MD,1 Silvina Busto, MD,

MPH,2 Clara Rive-Posse, MD, MPH,3 Guadalupe Verdejo MD, MPH,4 Maria Isabel Farace,

DVM,5 Francisco Rosetti, MS,5 Jorge A. San Juan, MD,6 Carlos Maria Julia, MD,MPH,3 John

Becher, RPh,1 Susan E. Maslanka, PhD, 1 David Swerdlow, MD1

1Centers for Disease Control and Prevention, 2Ministero de Salud-Region V, 3Ministero de

Salud y Accion Social, 4Pan American Health Organization, 5Departamento de Bacteriologia,

Instituto Nacional de Enfermedades Infecciosas, 6Hospital F. J. Muñiz, Buenos Aires, Argentina

Case study and instructor’s guide created by: Jeanette K. Stehr-Green, MD

NOTE: This case study is bas ed on a rea l-life outbrea k investigatio n underta ken in

Buenos Aires, Argentina, in 1998. Some aspects of the original outbreak and

investigation have been altered, however, to assist in meeting the desired teaching

objectives and allow completion of the case study in less tha n 3 hours. 

Students should be aware that this case study describes and promotes one particular

approac h to foodborne disea se outbrea k investigatio n. Procedu res and po licies in

outbreak investigations, however, can vary from country to country, state to state, and

outbreak to outbreak.

It is anticipate d that the ep idemiolo gist investiga ting a foodb orne disea se outbrea k will

work within the framework of a n “investig ation team” which inclu des perso ns with

expertise in epidemiology, microbiology, sanitation, food science, and environmental

health. It is through the collaborative efforts of this team, with each member playing a

critical role, that outbreak investiga tions are successfully com pleted. 

Please send us your comments on this case study by visiting our website at

http://www.phppo.cdc.gov/phtn/casestud . ies Please include the name of the case study

with your comments.

April 2002

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

Atlanta, Georgia 30333
STUDENT’S VERSION

Botulism in Argentina

Learning objectives:

After completing this case study, the student should be able to:

1. describe outbreak situations in which acute control measures should be undertaken

2. communicate information on an outbreak or outbreak investigation and write a press

release

3. given the leading hypothesis(es) in an outbreak, develop a questionnaire

4. given details on the origin, distribution, and preparation of an implicated food item,

identify critical points for the control of contamination and microbial survival and

growth

5. discuss possible barriers to implementation of specific interventions following an

outbreak investigation

6. describe measures that can be used to monitor the success of an intervention

7. describe the occurrence, signs and symptoms, and control of foodborne botulism

PART I - OUTBREAK DETECTION

Foodborne botulism is a severe illness that results from the ingestion of a preformed toxin

produced by a bacterium, Clostridium botulinum, in contaminated food. Death can occur in up

to 60% of untreated cases; supportive care and prompt administration of antitoxin have reduced

mortality in the United States to less than 10%. Outbreaks of botulism have been linked to

improperly preserved vegetables, fruits, and meats including fermented fish products, sausages,

smoked meat, and seafood.

On January 13, 1998, an infectious diseases physician at a Buenos Aires hospital telephoned the

Directorate of Epidemiology of the Argentine Ministry of Health (MOH) to report two possible

cases of botulism. The patients, both men, presented with drooping eyelids, double vision,

difficulty swallowing, and respiratory problems. One patient had onset of symptoms on January

5 and the other on January 6. The physician had drawn sera and collected stool specimens from

the men to test for botulinum toxin but no results were available.

Question 1: As a public health practitioner in Argentina, what are the major concerns raised by

these two possible cases of botulism in Buenos Aires?
Botulism in Argentina

Stude nt’s versio n - p. 2

The clinical syndrome of botulism is dominated by neurologic signs and symptoms. Dryness of

the mouth, drooping eyelids, and blurred and double vision are usually the earliest neurologic

complaints. These initial symptoms may be followed by disturbances in speech, difficulties

swallowing, and peripheral muscle weakness. If respiratory muscles are involved, ventilatory

failure and death may result unless supportive care is provided. The average incubation period

for botulism is 18-36 hours, but symptoms can occur as early as six hours or as late as 10 days

after exposure.

Because botulism is rare, many physicians are unfamiliar with its presentation. As a result,

patients with botulism can be misdiagnosed as other illnesses (e.g., stroke, myasthenia gravis,

Guillain-Barré syndrome) delaying the administration of life-saving botulinum antitoxin for days

and increasing the mortality rate among cases.

Question 2: How might you go about swiftly determining if there are other cases of botulism

associated with the cases in Buenos Aires?
Botulism in Argentina

Stude nt’s versio n - p. 3

The Directors of the National Laboratory and the Environmental Health and Sanitation Program

were notified of the possible cases of botulism. The two patients, still in the hospital, were

interviewed by an MOH epidemiologist. 

Upon questioning, it was learned that both patients were drivers for the same bus company and

drove the same route and shift. The patients knew each other but worked on different days of

the week. They had not eaten together in more than a month.

To find additional cases, the MOH contacted all employees of the bus company with the ill

drivers to see if any had symptoms suggestive of botulism. Hospitals in the area of Buenos

Aires, where the two cases occurred, were asked to report any patients with acute neurologic

illnesses that could be botulism. Family members of cases were questioned about whether they

also had symptoms of botulism. Additionally, the MOH developed a press release for

distribution to the local news media.

Question 3A: What key points would you include in the press release? 

Question 3B: Who should be involved in developing the press release or notified before its

distribution?
Botulism in Argentina

Stude nt’s versio n - p. 4

*

This is not the p ress release distributed by the Min istry of Health but was developed spe cifically for this 

 exercise.

On January 14, the MOH distributed the following press release:*

On Monday, January 13, two bus drivers, Pablo Esteban and Juan Rojas, from

south central Buenos Aires were diagnosed with botulism by an infectious

diseases physician at Hospital F. J. Muñiz. The men had been ill for several days

before the diagnosis was made. The attending physician, Dr. Jorge San Juan

reported that botulinum antitoxin was requested from the U. S. Centers for

Disease Control and Prevention last night.

Because botulism is potentially fatal if untreated, the Argentine Ministry of

Health is working with local public health officials and health care providers to

identify the source of the botulism. Officials worry that other persons may have

been exposed and need treatment or that the source may still exist and cause

more people to become ill.

Botulism is a rare but serious paralytic illness caused by a nerve toxin produced

by a bacterium, Clostridium botulinum. The symptoms of botulism can easily be

confused with other illnesses and include diplopia, ptosis, dysphagia, dysarthria,

and muscle weakness. If untreated, these symptoms may progress to cause

paralysis of the arms, legs, trunk and respiratory muscles, and ultimately death. 

If diagnosed early, botulism can be treated with an antitoxin which blocks the

action of the toxin circulating in the blood. 

Previous outbreaks of botulism in Argentina have been caused primarily through

eating improperly preserved vegetables and meats. Implicated foods include

ham, red and green peppers, vigcacha (an Andean rodent), eggplant, cucumbers,

palm hearts, tomatoes, peaches, spinach, and a type of cheese with onions. It is

not yet known what specific food may have caused the botulism in this outbreak

but both men are bus drivers for the same company, Arriba Bus, Inc., and drive

the same route and shift.

Persons who feel they or their relatives might have symptoms of botulism are

asked to contact the Directorate of Epidemiology of the Argentine Ministry of

Health at xxxx-xxxx .
Botulism in Argentina

Stude nt’s versio n - p. 5

Question 4: Critique the press release. How might the press release impact the outbreak

investigation?
Botulism in Argentina

Stude nt’s versio n - p. 6

Seven additional patients with neurologic signs consistent with botulism were identified. Five of

the patients had sought medical attention and four were hospitalized. Working diagnoses for

these patients at the time the initial two cases were discovered included myasthenia gravis (1), 

Guillain-Barré syndrome (2), stroke (1), and diabetic complications (1).

Botulinum toxin was identified in sera and/or stool from three patients, including one of the

original cases reported on January 13. 

All patients were drivers from the same bus company as the original cases and drove the same

route. From initial reports, all had eaten at a home located at the terminal stop of the bus route

where the drivers stopped during their breaks. Approximately 58 bus drivers worked this route;

27 in the morning shift, 16 in the afternoon shift, and 15 in the evening shift.

Question 5: Would you initiate any control measures at this time? What criteria would you

consider in implementing control measures so early in an investigation? 
Botulism in Argentina

Stude nt’s versio n - p. 7

PART II - DESCRIPTIVE EPIDEMIOLOGY AND HYPOTHESIS GENERATION

Staff from the local health department where the terminal stop of the bus route was located were

invited to participate in the investigation. 

Physicians attending the cases of botulism were asked to provide demographic and clinical

information on their patients. (Table 1)

Table 1. Characteristics of cases of botulism, Buenos Aires, January 1998.

Patient

No. 

Age

(years) Gender

Work

shift

Onset of neurologic symptoms Symptoms

1 42 M* Morning January 6 blurred vision, double vision,

drooping eyelids, upper and lower

extremity weakness, respirato ry

difficulty, fatigue

2 31 M Morning January 5 blurred vision, double vision,

drooping eyelids, upper and lower

extremity weakness

3 23 M Morning January 9 blurred vision, drooping eyelids,

upper extremity weakness, fatigue

4 46 M Morning January 8 drooping ey elids, difficulty

speaking

5 54 M Morning January 5 blurred vision, double vision,

drooping ey elids, difficulty

speaking, resp iratory difficu lty

6 49 M Morning January 10 blurred vision, drooping eyelids,

difficulty speaking

7 31 M Morning January 15 blurred vision, double vision,

drooping eyelids, upper and lower

extremity weakness, respirato ry

difficulty, fatigue

8 44 M Morning January 14 respiratory difficulty, fatigue,

drooping eyelids,

9 24 M Morning January 12 drooping eyelids, fatigue

*M=male gender
Botulism in Argentina

Stude nt’s versio n - p. 8

Question 6A: Summarize the demographic and clinical information on these patients and draw 

an epidemic curve. 

Question 6B: When was the most likely period of exposure among these cases?
Botulism in Argentina

Stude nt’s versio n - p. 9

In hypothesis-generating interviews with cases and other bus drivers, being a driver on the

morning shift of the bus route and eating at the terminal home of the route were the only

common exposures among cases. No cases of botulism occurred among bus drivers from the

afternoon or evening shift of the route. Bus drivers from those shifts did not usually eat at the

terminal home because it was only open for lunch. 

The investigators hypothesized that the outbreak was limited to morning shift bus drivers and

resulted from eating or drinking something at the home at the terminal stop of the particular bus

route between January 3 and 7.

Question 7: What type(s) of study would you use to investigate this hypothesis? Why?
Botulism in Argentina

Student’s version - p. 10

PART III - DESIGNING AN EPIDEMIOLOGIC STUDY TO TEST THE HYPOTHESIS

To identify the source of the outbreak, investigators undertook a retrospective cohort study

among bus drivers who drove the morning shift of the bus route. Data were collected from

January 15-19.

Investigators defined a confirmed case of botulism as a bus driver from the morning shift of the

bus route with a serum or stool sample that demonstrated botulinum toxin or yielded

Clostridium botulinum with onset of symptoms between January 5 and 15. A probable case was

defined as acute cranial nerve dysfunction (e.g., blurred vision, double vision, drooping eyelids,

problems swallowing) with no laboratory confirmation in this group of drivers during the same

period. The comparison group consisted of all bus drivers from the morning shift of the

implicated bus route who had no acute neurologic symptoms suggestive of botulism.

After consultation with the local health department where the terminal stop of the bus route was

located and the bus company management, investigators developed a structured questionnaire

for the epidemiologic study.

Question 8: What general types of information would you include in the questionnaire?
Botulism in Argentina

Student’s version - p. 11

Question 9: What steps would you take to develop the questionnaire for this investigation.

Question 10: Using information on foods served at the terminal stop home from January 3-7

(Appendix 1), draft questions for food exposure for this study. 
Botulism in Argentina

Student’s version - p. 12

Investigators conducted interviews with each of the drivers of the morning shift of the bus route

to complete the questionnaires.

Question 11: If the investigators had decided on self-administration of the questionnaire, what

changes might need to be made to it? 
Botulism in Argentina

Student’s version - p. 13

PART IV - ANALYSIS AND INTERPRETATION OF EPIDEMIOLOGIC RESULTS

The following food exposure information was collected through the cohort study. On January

19, the information was tabulated by epidemiologists from the Argentine MOH. (Table 2)

Table 2. Foods e aten by ill and well bus d rivers at the home at the terminal bus stop, Ja nuary 3-7, 1998 . 

(N=21)

Food item

Ate item Did not eat item

Ill Well Ill Well

Bologna 1 0 8 12

Hot dog 1 1 8 11

Matambre* 9 2 0 10

Mate** 4 4 5 3

Processed Ham 2 3 7 9

Sauce 7 2 2 10

Salami 1 1 8 11

Solid ham 2 3 7 9

*Matamb re is a traditio nal meat roll in Arge ntina. 

**Mate is green tea.

Question 12: Calculate the appropriate measures of association for these exposures. 
Botulism in Argentina

Student’s version - p. 14

Question 13: Interpret the results. What further data analysis/information might help?
Botulism in Argentina

Student’s version - p. 15

PART V - ENVIRONMENTAL STUDIES AND FOOD INVESTIGATION

Matambre is a traditional Argentine dish prepared from meat, vegetables, spices, and eggs. In a

traceback of the implicated matambre, the MOH discovered that it originated from a small scale

producer located not far from the terminal stop of the bus route. The matambre was purchased

at a local market on January 3 by the owners of the home that served the matambre. The MOH

initiated an environmental health assessment of the matambre to identify production factors that

could have contributed to the occurrence of botulism. 

A complete environmental health assessment is not a cursory inspection of operations and

sanitary conditions as is performed for the licensing of a food establishment, but focuses on the

suspect food or meal and follows it from its raw ingredients to consumption by the customer. 

The objective of the environmental health assessment is to identify critical points where the

implicated food could have become contaminated or microbial survival and growth in the food

could have occurred, determine why these conditions existed, and identify appropriate

interventions. The factors in Table 3, often found in these assessments, have been associated

with an increased risk of foodborne disease. 

Table 3. Factors that commonly contribute to outbreaks of foodborne diseases, from Bryan et al., 1987.

Contamination Survival Growth

raw foods that are contaminated

infected foodhandler

unclean equipment

cross-contamination

contaminated foods eaten

 raw or lightly cooked

inappropriate container for food

unsafe sources

added po isonous ch emicals

natural toxicant

poor dry-storage practices

inadequate cooking

inadequate reheating

inadequate acidification

inadequate refrigeration

improper cooling

inadequate hot-holding

preparation too far in advance

 of serving

use of leftover foods

inadequate acidification

high water content

inadequa te curing salt 

environment that provides

 favorable conditions for

 pathogen (e. g., anaerobic

 packaging)
Botulism in Argentina

Student’s version - p. 16

Question 14: What types of activities do you think you would undertake as part of an

environmental health assessment on the matambre? What equipment would you want to have?
Botulism in Argentina

Student’s version - p. 17

Clostridium botulinum is a spore-forming obligate anaerobic bacterium (i.e., it cannot grow in

the presence of oxygen). The spores are widespread in soil and dust worldwide. The toxin is

produced in improperly canned, low-acid or alkaline foods and in pasteurized and lightly cured

foods held without adequate refrigeration, especially in airtight containers. The toxin is

destroyed by boiling; inactivation of spores requires much higher temperatures.

Food safety inspectors from the local health department initiated the environmental health

assessment on January 20. The home at the terminal stop of the bus route was not formally

licensed or equipped as a restaurant. Perishable foods, such as the matambre, were kept in two

large refrigerators inside the home. Although the refrigerators were set at the coldest possible

setting, temperatures measured inside the refrigerators were 9°C and 10°C (48°F and 50°F,

respectively). 

The home owner reported the most recent matambre served in the home weighed approximately

4 kg. The matambre was cut into about 15 slices and was served in sandwiches, usually with a

spicy sauce; no other condiment or ingredient was added to the sandwiches. No matambre was

available for testing.

The implicated matambre was bought at a local market where it had been stored in a

refrigerator. The market had no temperature records or sales receipts; however, some customers

reported that the matambre had recently been sold at reduced prices because of power outages.

The market purchased matambre from a small scale commercial producer who made matambre

and processed hams in his home. To make matambre, the producer placed a slab of raw beef (1-

to 3-cm thick) on a stainless steel table. Ingredients included raw sliced carrots, hard-boiled

eggs, salt, red pepper flakes, dried oregano, and commercial potato flour. The meat was rolled

up around the vegetables and eggs to make an approximately 10 x 30 cm cylinder. The meat roll

was placed into a rectangular stainless steel pan to keep ingredients inside during cooking. 

Between 10 and 15 matambre in individual steel pans were immersed together in water heated to

70 to 80°C (158 to 176°F) and cooked approximately 4 hours. The matambre was never brought

to a boil. After cooking, the water was drained and the temperature was checked to ensure an

internal temperature of about 68°C (154°F). The producer placed each warm matambre in

plastic wrap, squeezed out the air, and sealed the plastic with heat. The plastic wrapped

matambre were allowed to cool, placed in a walk-in refrigerator, and were stored for up to 2

weeks before being sold to either supermarkets or directly to consumers.
Botulism in Argentina

Student’s version - p. 18

Question 15: Identify the foodhandling practices for the matambre which were most likely to

contribute to the development of botulism. 
Botulism in Argentina

Student’s version - p. 19

The producer reported making matambre every 2 weeks in batches of 15-20 each time. The last

batch produced before the outbreak was made in early December. No matambre were available

from that batch.

Question 16: What control measures would you initiate at this time? What difficulties might

you encounter?
Botulism in Argentina

Student’s version - p. 20

PART VI - CONTROL

After inspection by local food safety officials, the facility producing the matambre was closed. 

The producer was unable to provide receipts or a distribution list with locations where his

products were sold. He reported that most of his clients distributed his products in the western

greater Buenos Aires area. The producer’s matambre was not labeled in any way to indicate the

source or date of production, so a recall of any remaining matambre was not deemed feasible.

Based on data maintained by the MOH, botulism is not an uncommon occurrence in Argentina. 

During the years 1979-97, 277 cases of botulism were reported; for most, the source of the

exposure was undetermined. In 1997, 23 patients with suspected botulism were reported (of

which 13 [57%] died); about the same number of laboratory-confirmed cases were identified in

the United States, which has 10 times the population of Argentina. 

Question 17: Given the scope of the problem, what longer term interventions might help

decrease the number of botulism cases in Argentina?
Botulism in Argentina

Student’s version - p. 21

Because of the relatively high incidence and case fatality ratio for botulism in Argentina, the

MOH and Centers for Disease Control and Prevention (CDC) collaborated to establish a

botulism surveillance and antitoxin release system in Argentina. The system components

included: 1) the establishment of a local stock of antitoxin, 2) a mechanism for antitoxin

distribution within the country, 3) emergency notification and response for suspect cases

(including urgent epidemiologic investigation of the possible food source), and 4) laboratory

confirmation of suspect cases. 

Question 18: What is the rationale behind the components of this control effort?

Question 19: How might you monitor the Argentine botulism surveillance and antitoxin release

system over time to determine if it is effective?
Botulism in Argentina

Student’s version - p. 22

EPILOGUE

Although consumption of matambre is an established tradition in Argentina, it is usually

consumed fresh and is not generally intended for pickling or long-term preservation. Matambre

produced by licensed, commercial facilities use nitrites, acidifiers, or other preservatives to

prevent bacterial growth; the implicated matambre lacked these. Insufficient cooking, vacuum

packing in heat-shrinked wrap, and inadequate refrigeration may have provided conditions for

live spores to germinate and produce toxin.

The matambre that is believed to be the cause of the outbreak was cooked at relatively low

temperatures (78-80°C or 158-176°F ) over a time period of approximately 240 minutes, too

short to kill all C. botulinum spores. These spores are difficult to destroy using conventional

cooking techniques. In fact, nonkilling heat shock and the lack of preservatives or acidifiers

may even enhance germination and toxin elaboration.

To safely prepare foods for canning or long-term storage, the U.S. Department of Agriculture

recommends that all low-acid foods (i.e., foods with a pH > 4.6, including meats, seafood,

poultry, milk, and fresh vegetables) be sterilized at temperatures of 116 to 121°C (240-250°F) in

pressure canners operated at 0.66 to 0.97 atm (10-15 lb/in2). At these temperatures, the time

needed to destroy bacteria in low-acid canned food ranges from 20-100 minutes. The exact time

depends on the kind of food being canned, the way it is packed, and the amount of food being

cooked.
Botulism in Argentina

Student’s version - p. 23

REFERENCES

Villar RG, Shaprio RL, Busto S, et al. Outbreak of Type A botulism among bus drivers and

development of a botulism surveillance and antitoxin release system in Argentina. JAMA 1999;

281:1334-1340. 

Bryan FL, Anderson HW, Cook OD, et al. Procedures to investigate foodborne illness. 

International Association of Milk, Food, and Environmental Sanitarians, Inc.: Ames Iowa; 1987.

Centers for Disease Control and Prevention: Botulism in the United States, 1899-1996. 

Handbook for Epidemiologists, Clinicians, and Laboratory Workers, Atlanta, GA. Centers for

Disease Control and Prevention, 1998.

Shapiro RL, Hatheway C, Becher J, Swerdlow DL. Botulism surveillance and emergency

response. A Public Health Strategy for a Global Challenge. JAMA 1997; 278:433-435. 

Shapiro RL, Hatheway C, Swerdlow DL. Botulism in the United States: A clinical and

epidemiologic review. Annals of Internal Medicine 1998; 129:221-228.

St. Louis ME, Peck SHS, Bowering D, et al. Botulism from chopped garlic: Delayed recognition

of a major outbreak. Annals of Internal Medicine 1988; 108:363-68.

Townes JM. Cieslak PR, Hatheway CL, et a;. An outbreak of Type A botulism associated with a

commercial cheese sauce. Annals of Internal Medicine 1996;125:558-63.
Botulism in Argentina

Student’s version

APPENDIX 1

Foods served to bus drivers in home at terminal stop of bus route in the first week of 

January:

Bologna

Hot dogs

Matambre*

Mate**

Processed ham

Sauce

Salami

Solid ham

*Matambre is a traditional meat roll in Argentina. At the terminal stop it was sliced an d served in sandwich es, usually

with a spicy sauce.

**Mate is green tea.