Gastroenteritis at a University in Texas 

INSTRUCTOR’S VERSION

Original investigators: Nicholas A. Daniels,1 David A. Bergmire-Sweat,2 Kellogg J. 

Schwab,3 Kate A. Hendricks,2 Sudha Reddy,1 Steven M.. Rowe,1 Rebecca L. Fankhauser,1,4 

Stephan S. Monroe,1 Robert L. Atmar,3 Roger I. Glass,1 Paul S. Mead,1 Ree A. CalmesSlovin,5

 Dana Cotton,6 Charlie Horton,6 Sandra G. Ford,6 Pam Patterson6

1

Centers for Disease Control and Prevention, 2Texas Department of Health, 3Baylor College of 

Medicine, 4Atlanta Veterans Administration Medical Center, 5City of Huntsville, Health 

Inspections, 6Texas Department of Health, Region 6/5S 

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

NOTE: This case study is based on a real-life outbreak investigation undertaken in 

Texas 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 than 3 hours. 

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

approach to foodborne disease outbreak investigation. Procedures and policies in 

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

outbreak to outbreak.

It is anticipated that the epidemiologist investigating a foodborne disease outbreak will 

work within the framework of an “investigation team” which includes persons 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 investigations are successfully completed. 

We invite you to send us your comments about the case study by visiting our website at 

http://www.phppo.cdc.gov/phtn/casestudies. 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 
Target audience: epidemiologists and other persons with knowledge of basic epidemiologic

concepts and experience in data collection and analysis who are interested in learning specific

skills for investigating infectious disease outbreaks 

Trainee prerequisites: working knowledge of descriptive epidemiology, epidemic curves,

measures of association, stratified analysis, study design, outbreak investigation. The student

will also benefit from having some familiarity with food microbiology and environmental

investigation techniques but will be likely to rely heavily on others with greater expertise in

these areas in a real-life outbreak situation.

Teaching materials required: calculator

Time required: approximately 2 hours and 30 minutes

Language: English

Level of case study: Basic Intermediate X Advanced 

Materials borrowed from: 

“Foodborne Illness Investigation and Control Reference Manual”, Massachusetts Department of

Public Health, Division of Epidemiology and Immunization, Division of Food and Drugs, and

Division of Diagnostic Laboratories (1997)

“Guidelines for the Investigation and Control of Foodborne Disease Outbreaks”, World Health

Organisation, Food Safety Unit Division of Food and Nutrition and Division of Emerging and

Other Communicable Diseases Surveillance and Control (DRAFT, 1999)

Reviewed by:

Steve Luby, MD Centers for Disease Control and Prevention

Rob Tauxe, MD, MPH, Centers for Disease Control and Prevention

Richard Dicker, MD, MPH, Centers for Disease Control and Prevention

Thomas Grein, MD, MPH, World Health Organization

Allison Hackbarth, MPH, Massachusetts Department of Public Health

Patty Griffin, MD, MPH, Centers for Disease Control and Prevention

Chris Zahniser, RN, MPH, Centers for Disease Control and Prevention

Denise Werker, MD, MHSc, FRCPC, Laboratory Centre for Diseases Control, Health Canada

Mahomed Patel, MBChB, National Centre for Epidemiology and Population, Australia National

 University

Joseph Bresee, MD, Centers for Disease Control and Prevention

Cover art by: Barbara Orisich, MS 

Training materials funded by: the Centers for Disease Control and Prevention (National

Center for Infectious Diseases, Food Safety Initiative, Public Health Practice Program Office,

and Epidemiology Program Office/Division of International Health)
INSTRUCTOR’S VERSION

Gastroenteritis at a University in Texas

Learning objectives:

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

1. list categories and examples of questions that should be asked of key informants who

report a suspected outbreak of foodborne disease 

2. list four criteria for prioritizing the investigation of suspected foodborne disease

outbreaks 

3. list three common pitfalls in the collection of clinical specimens for the investigation

of suspected foodborne diseases

4. determine the most efficient epidemiologic study design to test a hypothesis (including

the case definition and the appropriate comparison group)

5. describe the advantages and disadvantages of different forms of questionnaire

administration (e.g., self-administered, telephone, in-person)

6. list key areas of focus in interviewing foodhandlers and observing kitchen practices in

a foodborne disease outbreak

PART I - OUTBREAK DETECTION

On the morning of March 11, the Texas Department of Health (TDH) in Austin received a

telephone call from a student at a university in south-central Texas. The student reported that he

and his roommate, a fraternity brother, were suffering from nausea, vomiting, and diarrhea. 

Both had become ill during the night. The roommate had taken an over-the-counter medication

with some relief of his symptoms. Neither the student nor his roommate had seen a physician or

gone to the emergency room.

The students believed their illness was due to food they had eaten at a local pizzeria the previous

night. They asked if they should attend classes and take a biology midterm exam that was

scheduled that afternoon.

Question 1: What questions (or types of questions) would you ask the student?

In recording a complaint about a possible foodborne illness, it is important to systematically

collect the following information:

• WHAT is the person’s problem? (e.g., clinical description of the illness, whether a

physician was consulted, whether any tests were performed or any treatments were

provided)
Gastroenteritis at a University in Texas

Instructo r’s version - p. 2

• WHO else became ill, their characteristics (e.g., age, sex, occupation), and the nature of

their illnesses (e.g., symptoms, whether any persons were hospitalized or died)?

• WHEN did the affected person(s) become ill?

• WHERE are the affected persons located? (including names and telephone numbers)

• WHY (and HOW) do they think they became ill? (e.g., risk factors, suspected exposures,

suspected modes of transmission, hints from who else did and did not become ill)

NOTE:

1) Always collect as much information as possible from the person reporting an illness the

first time contact is made; it might be difficult to talk with the person again. If the

complainant cannot provide critical pieces of information, try to find out who may be

able to and contact that person. Be sure to ask the reporter how s/he can be reached in

the future and if anyone else has been notified of this problem.

2) Collect information on pertinent negatives as well as pertinent positives. For example, if

one only records that the person’s symptoms included vomiting and diarrhea, it is

difficult to know if that means there was no fever or the information was not collected. 

3) Collect a complete food history. Regardless of the source, complainants will often

associate illness with the last food or meal they consumed (particularly if it was at a

commercial establishment). 

• If the etiologic agent is not known, obtain at least a 72-hour food history (i.e., all

foods/beverages/meals consumed in the 72 hours prior to onset of illness). 

• For illnesses in which diarrhea is the predominant symptom (as opposed to

vomiting), one should collect a 5-day food history because incubation periods for

diarrheal diseases tend to be longer. 

• If the etiologic agent is known, ask about foods/beverages/meals eaten within the

incubation period for that illness. 

• If more than one person is reported ill, foods/beverages/meals COMMON to all

persons will be of particular interest BUT complete food histories for the

appropriate time periods should still be collected.

4) Remember that many illnesses that can be acquired through foods may also be acquired

through other means such as water, person-to-person contact, and animal-to-person

contact. Keep an open mind about possible sources and do not assume that it must be

food.
Gastroenteritis at a University in Texas

Instructo r’s version - p. 3

5) Be sure to accurately record symptoms, dates and times of the onset of illness, and dates

and times of food consumption. Most people who have experienced a recent illness

should be able to provide you with these answers.

6) Thank the person for notifying you of their illness. 

Question 2: What would you advise the student about attending classes that day?

You probably should refer the student to his personal physician or the Student Health Center for

a complete assessment. 

While symptomatic, the students would probably be most comfortable staying in their dorm

room. With adequate hygienic practices, however, they can return to normal activities

(excluding foodhandling and direct care of high risk persons [e.g., infants, elderly,

immunocompromised, or institutionalized persons]). Persons involved in foodhandling and

direct care of high risk persons should not return to work until 48-72 hours after symptoms have

resolved. For selected illnesses, the local jurisdiction may require 1-3 negative stool specimens

collected at least 48 hours after completion of any antibiotic treatment. One should check local

isolation and quarantine policies for clarification.

The “Foodborne Illness Complaint Worksheet” (Appendix 1) was completed based on the call. 

The student refused to give his name or provide a telephone number or address at which he or

his roommate could be reached.

Question 3: Do you think this complaint should be investigated further? 

Ideally, all reports of possible outbreaks of foodborne illnesses should be investigated to:

1) prevent other persons from becoming ill (either from the same food or method of food

preparation), 

2) identify potentially problematic foodhandling practices, and 

3) add to our knowledge of foodborne diseases. 

Given current resource constraints in many health departments, however, it may not be possible

to investigate all individual cases or investigate all cases to the same degree. Therefore, public

health workers often must choose which instances receive highest priority for investigation. 

The most important diseases/complaints to investigate are those that are a severe threat to the

public’s health or where a timely control response is critical. Top priorities include:
Gastroenteritis at a University in Texas

Instructo r’s version - p. 4

• an outbreak associated with a commercially distributed food product

• severe (life-threatening) illnesses such botulism or E. coli O157:H7 infection

• confirmed clusters of a similar illness that appear to be associated with a specific food

preparer or food service establishment

• instances where a large number of people appear to be affected

• indications of adulterated food presenting an imminent danger

• foodborne illness in a foodhandler

Clues that a follow-up investigation may not be warranted or is unlikely to be productive

include:

• signs and symptoms (or confirmed diagnoses) among affected individuals suggesting they

might not have the same illness

• ill persons who are not able to provide adequate information for investigation including

date and time of onset of illness, symptoms, or a complete food history

• confirmed diagnosis and/or clinical symptoms that are not consistent with the foods

eaten and the onset of illness

• repeated complaints made by the same individual(s) for which prior investigations

revealed no significant findings

In this foodborne disease complaint, one might be a little skeptical. First, if the illness was due

to food consumed the night before, the incubation period would have been relatively short,

suggesting a preformed toxin. The students’ symptoms (e.g., diarrhea and fever), however, are

more consistent with an enteric infection; infections tend to have longer incubation periods (i.e.,

$6 hours as opposed to <6 hours as seen with intoxications). Secondly, the student refused to

give a food history beyond the foods eaten at the pizzeria. Finally, the question about attending

classes and taking a midterm exam sounds as if the roommates might just want an excuse to

avoid an unpleasant situation (particularly if they did not study sufficiently!)

NOTE: The fact that the student was not willing to give his or his roommate’s name should not

be over interpreted. Anonymous complaints are not uncommon and do not automatically

invalidate a complaint. Complainants often request anonymity for fear of retribution.

TDH staff were skeptical of the student’s report but felt that a minimal amount of exploration

was necessary. They began by making a few telephone calls to establish the facts and determine

if other persons were similarly affected. The pizzeria, where the student and his roommate had

eaten, was closed until 11:00 A.M. There was no answer at the University Student Health

Center, so a message was left on its answering machine.
Gastroenteritis at a University in Texas

Instructo r’s version - p. 5

A call to the emergency room at a local hospital (Hospital A) revealed that 23 university 

students had been seen for acute gastroenteritis in the last 24 hours. In contrast, only three

patients had been seen at the emergency room for similar symptoms from March 5-9, none of

whom were associated with the university.

At 10:30 A.M., the physician from the University Student Health Center returned the call from

TDH and reported that 20 students with vomiting and diarrhea had been seen the previous day. 

He believed only 1-2 students typically would have been seen for these symptoms in a week. 

The Health Center had not collected stool specimens from any of the ill students.

Question 4: Do you think these cases of gastroenteritis represent an outbreak at the university? 

Why or why not?

An outbreak is the occurrence of more cases of a disease than expected for a particular place

and time. In a 2-day period, over 40 cases of gastroenteritis occurred among students at the

university (assuming that individual students did not visit both the Student Health Center and

the emergency room). This compares with the handful of students that would normally have

been seen for these symptoms at the two facilities in a week. Therefore, it is highly likely that

these cases represent an outbreak. 

What is not clear is whether the outbreak is limited to the university or if the wider community 

may also be affected. Case finding methods to this point, a hospital near the university and the

University Student Health Center, are more likely to pick up cases among students than in the

community.

NOTE: The terms “outbreak” and “epidemic” are used interchangeably by most

epidemiologists. The term “outbreak” is sometimes preferred, particularly when talking to the

press or public, because it is not as frightening as “epidemic”. 
Gastroenteritis at a University in Texas

Instructo r’s version - p. 6

PART II - INITIAL MICROBIOLOGIC INVESTIGATION

On the afternoon of March 11, TDH staff visited the emergency room at Hospital A and

reviewed medical records of patients seen at the facility for vomiting and/or diarrhea since

March 5. Based on these records, symptoms among the 23 students included vomiting (91%),

diarrhea (85%), abdominal cramping (68%), headache (66%), muscle aches (49%), and bloody

diarrhea (5%). Oral temperatures ranged from 98.8/F (37.1/C) to 102.4/F (39.1/C) (median:

100/F [37.8/C]). Complete blood counts, performed on 10 students, showed an increase in white

blood cells (median count: 13.7 per cubic mm with 82% polymorphonuclear cells, 6%

lymphocytes, and 7% bands). Stool specimens had been submitted for routine bacterial

pathogens, but no results were available.

Question 5: List the broad categories of diseases that must be considered in the differential

diagnosis of an outbreak of acute gastrointestinal illness.

There are two broad classifications for enteric diseases:

• Infections are a consequence of the growth of a microorganism in the body. Illness

results from two mechanisms: 1) viruses, bacteria, or parasites invade the intestinal

mucosa and/or other tissues, multiply, and directly damage surrounding tissues and 2)

bacteria and certain viruses invade and multiply in the intestinal tract and then release

toxins that damage surrounding tissues or interfere with normal organ or tissue function. 

The necessary growth of the microorganism (for production and release of toxins) takes

time; thus, the incubation periods for infections are relatively long, often measured in

days compared with hours as are seen with intoxications. Symptoms of infection usually

include diarrhea, nausea, vomiting, and abdominal cramps. Fever and an elevated white

blood count are often associated with infection.

• Intoxications are caused by ingestion of food already contaminated by toxins. Sources of

toxin include certain bacteria, poisonous chemicals, and toxins found naturally in

animals, plants, or fungi. Intoxications most often result from bacteria that release

toxins into food during growth in the food. The preformed toxin is ingested, thus live

bacteria do not need to be consumed to cause illness. Illness from a toxin manifests

more rapidly than that due to an infection because time for growth and invasion of the

intestinal lining is not required. The incubation period for an intoxication is often

measured in minutes or hours. The most common (and sometimes only) symptom of an

intoxication is vomiting. Other symptoms can range from nausea and diarrhea to

interference with sensory and motor functions such as double vision, weakness,

respiratory failure, numbness, tingling of the face, and disorientation. Fever is rarely

present with intoxication.

See Appendix 2 for a list of common enteric disease agents in each of these categories.
Gastroenteritis at a University in Texas

Instructo r’s version - p. 7

Question 6: How might you narrow the range of agents suspected of causing the gastrointestinal

illness?

The following information might help shorten the list of suspected agents:

• predominant signs and symptoms

• incubation period

• duration of symptoms

• suspect food

• laboratory testing of stool, blood, or vomitus

TDH staff asked health care providers from the University Student Health Center, the Hospital A

emergency room, and the emergency departments at six other hospitals located in the general

vicinity to report cases of vomiting or diarrhea seen since March 5. A TDH staff person was

designated to help the facilities identify and report cases. The health care providers were also

asked to collect stool specimens from any new cases. Bacterial cultures from patients seen in

the emergency rooms were to be performed at the hospital at which they were collected and

confirmed at the TDH Laboratory. Specimens collected by the Student Health Center were to be

cultured at the TDH Laboratory.

Question 7: What information should be provided with each stool specimen submitted to the

laboratory? How will the information be used?

The following information should be submitted with each stool specimen:

• patient’s name or identification number - used to track and provide results; allows

comparison of results from repeat specimens

• date of collection of specimen - along with date of onset of symptoms, this date helps the

laboratory determine where in the course of the patient’s illness the specimen was

collected (and, therefore, the likelihood of isolating an etiologic agent); also allows the

laboratory to determine the age of the specimen when they receive/process it (i.e.,

determine if it is old)

• date of onset of symptoms - along with the date of collection of the specimen, this date

helps the laboratory determine where in the course of the patient’s illness the specimen

was collected (and, therefore, the likelihood of isolating an etiologic agent) 

• signs and symptoms - may suggest a particular agent and lead the lab to perform specific

testing (e.g., bloody diarrhea may suggest the need to culture for E. coli O157:H7 or

other Shiga-like toxin producing E. coli)
Gastroenteritis at a University in Texas

Instructo r’s version - p. 8

Question 8: How should specimens be transported from the University Health Center to the

TDH laboratory?

NOTE: One should check with the laboratory that will be testing the specimens for any

collection, storage, or transportation recommendations. In general, collection and storage of

stool specimens will depend on the examinations to be performed. Appendix 3 (in both the

student and instructor versions) includes the following information:

For bacterial pathogens

Rectal swabs or swabs of fresh stools should be placed in refrigerated Cary-Blair transport

medium. If the specimens are likely to be examined within 48 hours after collection, they can be

refrigerated at 4°C until shipping. Specimens should be enclosed in a secure container and

placed in a waterproof bag. Specimens should be packed with ice or frozen refrigerant packs in

an insulated box.

If specimens must be held longer than 48 hours, they should be frozen as soon as possible after

collection. Although storage in an ultra-low freezer (-70°C) is preferable, storage in a hometype freezer (if it is properly set at -20°C) is acceptable for short periods. So that the specimens 

remain frozen, they should be shipped on dry ice. Sufficient dry ice should be used to keep

specimens frozen until the laboratory processes them (i.e., enough dry ice to fill one-third to

one-half of the shipping container). Glass tubes should not be in direct contact with dry ice; a

layer of paper or other material should be placed between the tubes and the dry ice. To prevent

excess exposure to carbon dioxide (from the dry ice), screw caps should be tightened and sealed

with electrical tape or specimens should be sealed in a plastic bag within the container of dry

ice.

For viral pathogens

Collect as large a quantity of diarrheal stool as can be obtained (at least 10 cc). Place in a

leak-proof, clean, dry container, and refrigerate immediately at 4°C. DO NOT FREEZE

SPECIMENS IF ELECTRON MICROSCOPY EXAMINATION IS ANTICIPATED. The use of

rectal swabs to detect viral causes of gastroenteritis is discouraged because the sensitivity of

detection compared to bulk stool is suspected to be low.

For parasites

Mix fresh bulk stool specimens thoroughly with each of two preservatives, 10% formalin and

polyvinyl alcohol fixative, at a ratio of one part of stool to 3 parts of preservative. If there is

any delay in obtaining the preservatives, refrigerate untreated stool specimens at 4°C for up to

48 hours. For routine microscopy DO NOT FREEZE. Once preserved, the specimens can be

stored and transported at room temperature or refrigerated. Note, it is now possible to do

genotyping on many parasites, but this may require different preservatives. If parasites are

considered a likely etiology, contact a lab that has the capacity to conduct genetic testing and

ask for specific instructions. 
Gastroenteritis at a University in Texas

Instructo r’s version - p. 9

Later that afternoon, preliminary culture results from 17 ill students became available. The

specimens, collected primarily from the emergency room at Hospital A on March 10, did not

identify Salmonella, Shigella, Campylobacter, Vibrio, Listeria, Yersinia, Escherichia coli

O157:H7, Bacillus cereus, or Staphylococcus aureus. Some specimens were positive for fecal

leukocytes and fecal occult blood.

Question 9: How might you interpret the bacterial culture results? What questions do these

results raise?

Several explanations may exist for the negative cultures:

• Specimens may have been mishandled during storage or transport leading to the death of

any biological pathogen present.

• Specimens may have been mishandled during processing or culture leading to the death

of any biological pathogen present.

• Specimens may have been collected too late in the course of the patients’ illnesses (i.e.,

the patients were no longer excreting the pathogen in adequate numbers for detection).

• The illness may be due to some agent not tested for by the laboratory (e.g., virus or

bacterial pathogen not routinely identified, parasite, preformed toxin, chemical agent).

Since the cultures were performed in house at Hospital A, it would seem that transportation

difficulties (and aging of specimens) would not be a large problem. Most of the specimens were

collected on March 10, shortly after the students became symptomatic. For most infectious

agents, patients would still be shedding microorganisms at that point in their illness. We do not

know about the reputability of the Hospital A laboratory or whether there may have been some

temporary problems with processing the specimens. The fact that all 17 specimens were

negative suggests either the laboratory had a very big problem or, indeed, the cultures were

negative for the pathogens examined. If we assume that laboratory procedures were acceptable,

it seems likely that the agent causing the illness was not detected because it was not tested for.
Gastroenteritis at a University in Texas

Instructor’s version - p. 10

PART III - DESCRIPTIVE EPIDEMIOLOGY AND HYPOTHESIS GENERATION

By March 12, seventy-five persons with vomiting or diarrhea had been reported to TDH. All

were students who lived on the university campus. No cases were identified among university

faculty or staff or from the local community. Except for one case, the dates of illness onset were

March 9-12. (Figure 1) The median age of patients was 19 years (range: 18-22 years), 69%

were freshman, and 62% were female.

Figure 1. Onset of gastroenteritis among students, University X, Texas, March 1998. (N=72) (Date of

onset was not know n for three ill students.)
Gastroenteritis at a University in Texas

Instructor’s version - p. 11

TDH staff met with the Student Health Center physician and nurse, and several university

administrators including the Provost. City health department staff participated in the meeting.

Question 10: What topics would you include in discussions with university officials?

In the meeting, investigators would want to: 1) negotiate cooperation with the university

officials so that the investigation will go smoothly and 2) collect information that might provide

insights into the source of the outbreak. 

To negotiate cooperation from university officials, one should cover:

• why it is important to investigate the outbreak (especially, to the university, itself) and to

do so in a timely fashion

• what has already been done and found to date

• what is planned

• what the health department can provide to the university

• what kind of cooperation will be needed from the university (food samples, menus, time

and place to interview foodhandlers and managers, etc.)

• how press inquiries will be handled

• how the university will be kept informed of progress in the investigation

To collect information on possible sources of the outbreak, one might ask questions about:

• the population at risk (e.g., the size and characteristics of the student body) 

• possible sources for enteric diseases including water supplies and sewage systems (e.g.,

source of water, treatment of water and sewage if done locally, recent breaks in water

and/or sewage lines), sources of food for students (e.g., number and distribution of

dining establishments on campus, meal plans, sources of food for each of the

establishments [central vs. site specific]), possible contact with animals (e.g., animal

husbandry classes, special events [e.g., rodeos]), and living arrangements for students

(e.g., number and distribution of residential halls).

TDH and City Health Department staff gathered the following information:

The university is located in a small Texas town with a population of 27,354. For the

spring semester, the university had an enrollment of approximately 12,000 students;

2,386 students live on campus at one of the 36 residential halls scattered across the 200+

acres of the main campus. About 75% of the students are Texas residents.

The university uses municipal water and sewage services. There have been no breaks or

work on water or sewage lines in the past year. There has been no recent road work or

digging around campus.
Gastroenteritis at a University in Texas

Instructor’s version - p. 12

The campus dining service includes two cafeterias managed by the same company and

about half a dozen fast food establishments; about 2,000 students belong to the university

meal plan which is limited to persons living on campus. Most on-campus students dine

at the main cafeteria which serves hot entrees, as well as items from the grill, deli bar,

and a salad bar. A second smaller cafeteria on campus offers menu selections with a per

item cost and is also accessible to meal plan members. In contrast to the main cafeteria,

the smaller cafeteria tends to be used by students who live off campus and university

staff. The smaller cafeteria also offers hot entrees, grilled foods, and a salad bar, but has

no deli bar. 

Spring break is to begin on March 13 at which time all dining services will cease until

March 23. Although many students will leave town during the break, it is anticipated

that about a quarter of those living on campus will remain.

Hypothesis generating interviews were undertaken with seven of the earliest cases reported by

the emergency rooms and the Student Health Center; all of the cases had onset of illness on

March 10. Four were male and three were female; all but one was a freshman. Two students

were psychology majors; one each was majoring in English and animal husbandry. Three

students were undecided about their major. 

The students were from five different residential halls and all reported eating most of their meals

at the university’s main cafeteria. During the past week, all but one student had eaten food from

the deli bar; two had eaten food from the salad bar, and three from the grill. Seven-day food

histories revealed no particular food item that was common to all or most of the students. 

Except for the psychology majors, none of the other students shared any classes; only one

student had a roommate with a similar illness. Five students belonged to a sorority or a

fraternity. Three students had attended an all school mixer on March 6, the Friday before the

outbreak began; two students went to an all night science fiction film festival at one of the

dorms on March 7. Students reported attendance at no other special events; most had been

studying for midterm exams for most of the weekend.

Question 11: Using information available to you at this point, state your leading hypothesis(es)

on the pathogen, mode of transmission, source of the outbreak, and period of interest. 

Pathogen: Signs and symptoms among students (i.e., vomiting, diarrhea, fever, bloody stools,

fecal leucocytes, and fecal occult blood) are consistent with an acute gastrointestinal infection. 

The negative bacterial cultures (which covered the usual bacterial agents) suggest the pathogen
Gastroenteritis at a University in Texas

Instructor’s version - p. 13

might be a virus or a parasite. Signs and symptoms among students (i.e., high prevalence of

vomiting and diarrhea) are more common among viral infections than a parasitic infection, but

could be seen in both. Although the incubation period is unknown, the quick upswing in the

epicurve with a rapid decline in cases suggests a relatively short exposure and incubation

period (i.e., a few days), again, more suggestive of a virus than a parasite. (NOTE: The

duration of symptoms, which is not known at this point, would also be helpful in distinguishing

between a viral infection [hours to days] and a parasitic infection [weeks].)

Mode of transmission: Illness is limited to students living on campus. The campus uses city

water supplies. If city water supplies were contaminated, one would also expect to see cases in

the community. It is possible that there are isolated problems with water and sewer lines on

campus, but students from at least five residential halls were affected, so a break would have to

affect water distribution over a wide area. (And if campus water was widely contaminated, one

might expect to see illness in faculty, staff, and off-campus students who consumed water while

on campus.) 

Cases occurred in a number of different residential facilities and, among hypothesis generating

interviews, did not cluster by dorm rooms (i.e., roommates were not affected), or classes. This

pattern is not consistent with person-to-person spread.

A large proportion of students living on campus are part of the meal plan; most on-campus

students eat at the main dining room. University staff and off-campus students rarely eat at the

main cafeteria. All students in the hypothesis generating interviews ate at the main cafeteria

and most also ate at the deli bar suggesting contaminated food or drink from this site might be

the mode of transmission. 

Source: No common food items were identified through hypothesis generating interviews. 

However, viral agents are commonly transmitted through raw or poorly cooked shellfish,

sandwiches, and salads.

Period of interest: The incubation periods for viral gastroenteritities range from less than a day

to about a week. The majority of cases had an onset of illness from March 10 - 12. Counting

back the minimum incubation period (< 1 day) from the earliest cases and the maximum

incubation period (7 days) from the latest cases suggests exposure between March 5 and 10.

LEADING HYPOTHESIS: a viral infection spread by a food or beverage served at the

university main cafeteria between March 5 and 10
Gastroenteritis at a University in Texas

Instructor’s version - p. 14

Question 12: What actions would you take? 

At this point, findings are only suggestive that food from the main cafeteria is the source of the

outbreak. Exposures common among cases may be common among all students living on

campus; therefore, it would seem that insufficient information exists to undertake effective

control measures at this time. 

Next steps in this investigation include a controlled epidemiologic study, an environmental

investigation of the main cafeteria and deli bar (e.g., inspection of operations and interviews

with staff), viral testing of stool specimens from ill persons, and collection and testing of leftover

food, water, and ice from the main cafeteria and deli bar. 
Gastroenteritis at a University in Texas

Instructor’s version - p. 15

PART IV - ENVIRONMENTAL INVESTIGATION

Based on clinical findings, the descriptive epidemiology of early cases, and hypothesisgenerating interviews, investigators hypothesized that the source of the outbreak was a viral

pathogen spread by a food or beverage served at the main cafeteria at the university between

March 5 and 10. As a result, TDH environmental sanitarians inspected the main cafeteria and

interviewed staff on March 12.

Thirty-one staff members were employed at the cafeteria of whom 24 (77%) were foodhandlers. 

Except for one employee who worked at the deli bar and declined to be interviewed, all dining

service personnel were interviewed.

Question 13: What key areas should be explored during interviews with the cafeteria

foodhandlers? 

Items to cover with foodhandlers include: (in order of importance)

1) Identify food items served at the main cafeteria (particularly the deli bar) during the

implicated time period.

2) Determine whether any kitchen staff or their family members were ill at the time of the

outbreak.

3) Describe handwashing facilities at the cafeteria and routine hygienic practices of

foodhandlers.

4) Collect stool specimens from all foodhandlers.

5) Watch or reconstruct the procedures in the kitchen (in handling/preparing the food

items) that happened the days it is believed the contaminated food was prepared. Try to

identify any unusual occurrences or departures from routine during the implicated time

period.

6) Outline work schedules for foodhandlers during the implicated period and identify who

was responsible for what on which days.

7) Get recipes for food items served during the implicated time period and identify the

ingredients and their sources.

Cafeteria staff were questioned about their responsibilities in the cafeteria such as the foods they

handled, which meals they served, and where they usually worked (e.g., deli bar, grill). They

were also asked about use of gloves, handwashing practices, their work schedule during the

week before the outbreak, and if they had been ill at that time. 

In the cafeteria, the deli bar had its own preparation area and refrigerator. During mealtimes,

sandwiches were made to order by a foodhandler. Each day, newly prepared deli meats,
Gastroenteritis at a University in Texas

Instructor’s version - p. 16

cheeses, and condiments were added to partially depleted deli bar items from the day before

(i.e., without discarding leftover food items). While the deli was open for service, sandwich

ingredients were not kept refrigerated or on ice. The deli bar containers were not routinely

cleaned. Samples of leftover food, water, and ice were collected.

None of the foodhandlers interviewed reported being ill in the last two weeks. Stool cultures

were requested from all cafeteria staff. 

Before dinner on March 12, the City Health Department closed the deli bar.

Question 14: Do you agree with the decision to close the deli bar? What actions would you take

now?

There is no solid evidence to implicate the deli bar as the source of the outbreak. The action is

based on the most likely hypothesis and circumstantial evidence (i.e., other foodhandling

problems identified in the deli bar). Because there were multiple serious problems identified at

the deli bar, closing it down until safer practices can be assured would seem reasonable. 

Furthermore, closure will be a minimal burden to the university and its students and could

prevent additional cases from occurring.

Although the suspected source of the outbreak has seemingly been addressed, it is important to

undertake a more definitive epidemiologic study for the following reasons:

• the source may not be the deli bar and cases may continue to occur

• more specific information is needed on the source to determine when it is safe to reopen

the deli bar

• more specific information is needed on the source to prevent the problem from recurring

in the future
Gastroenteritis at a University in Texas

Instructor’s version - p. 17

PART V - DESIGNING AN EPIDEMIOLOGIC STUDY TO TEST THE HYPOTHESIS

(STUDY #1)

On the evening of March 12, about 36 hours after the initial call to the health department, TDH

staff conducted a matched case-control study among students at the university. Ill students

(reported from emergency rooms and the Student Health Center) who could be reached at their

dormitory rooms were enrolled as cases. Dormitory roommates who had not become ill were

asked to serve as matched control subjects. Investigators inquired about meals the students

might have eaten during March 5-10 and where the foods were eaten. All information was

collected over the telephone.

Question 15: What are the advantages and disadvantages of undertaking a case-control study

instead of a cohort study at this point in the investigation?

At this point, the goal of the epidemiologic study is to find the source of the outbreak. The

population at risk is well-defined and consists of students living on campus. The primary

exposure of interest is eating at the main cafeteria. The outcome is relatively rare (i.e., only 75

cases or approximately 3% of the 2,400 students living on campus are known to be ill) and the

suspected exposure (the main cafeteria) is common (i.e., about 2000 or 84% of the students

living on campus have meal tickets). With unlimited resources, one could do either a cohort or

a case-control study to investigate the source of this outbreak. 

A retrospective cohort study would include all students living on campus, comparing those who

ate at the main cafeteria during the period of interest with those who did not. A cohort study

would allow one to calculate the risk of disease among students living on campus, an added

bonus. With the large number of students in the cohort, however, a cohort study would be costly

and take a lot of time, and response rates are likely to be poor. If a random sample of the cohort

were selected (a more doable undertaking), the number of cases included in the study is likely to

be small, decreasing the power of the study to find a source of the outbreak.

A case-control study would compare students with the illness (cases) with a sample of students

without the illness (controls). It would allow one to limit the number of subjects involved in the

study, include a sufficient number of cases to assure adequate study power, and focus one’s

efforts on the smaller number of subjects to get higher participation/response rates. Although a

case-control study would not allow one to directly calculate attack rates, it would be much

cheaper and quicker to undertake than a cohort study. As a result, it would seem that a casecontrol study would be the most cost-effective study type at this juncture.
Gastroenteritis at a University in Texas

Instructor’s version - p. 18

Question 16: How would you define a case for this study? 

A case definition is a standard set of criteria for deciding whether an individual should be

classified as having the disease of interest. A case definition includes clinical criteria (e.g.,

signs, symptoms, and laboratory tests) and restrictions on time, place, and person. It is

important not to include the hypothesis being tested (e.g., eating at the main cafeteria) in the

case definition.

Because initial laboratory tests among ill persons in this outbreak were negative, the clinical

component of the case definition will be based largely on signs and symptoms. Predominant

symptoms among persons seen at the Hospital A emergency room included “vomiting” and/or

“diarrhea”. Because humans naturally experience changes in bowel patterns (e.g., consistency

and number) on a day-to-day basis, “diarrhea” among cases needs to be defined in such a way

as to exclude as many well persons with these natural variations as possible. For this study, a

case was defined as vomiting or diarrhea ($3 loose bowel movements during a 24-hour period)

with onset on or after March 5, 1998, in a student from the university seen at an emergency

room or the Student Health Center.

Twenty-nine cases and controls were interviewed over the telephone. Investigators tabulated the

most notable results in Table 1. 

Table 1. Risk factors for illness, matched case-control study, main cafeteria, University X, Texas, March

1998.

Exposure

Ill exposed/

Total ill* (%)

Well exposed/

Total well* (%)

Matched

Odds

Ratio**

95%

Confidence

Interval p-value

Ate at deli bar - 

lunch on March 9

11/28 (39) 1/29 (3) 11.0 1.6-473 <0.01

Ate at deli bar -

dinner on March 9

7/27 (26) 2/29 (7) 6.0 0.73-275 0.06

Ate at deli bar - 

lunch on March 10

8/29 (28) 1/28 (4) 8.0 1.1-354 0.02

Ate at deli bar -

dinner on March 10

2/29 (7) 2/28 (7) 1.0 0.01-79 0.75

Ate at deli bar - lunch

or dinner March 9 or

lunch March 10

15/27 (56) 3/28 (11) 7.0 1.61-63.5 <0.01

*Denominator does not always total to 29 because several subjects could not remember where they ate the indicated

meal. 

**The data pro vided for cases an d contro ls cannot b e used to calculate the m atched od ds ratio whic h is based o n an

analysis of discordant pairs.
Gastroenteritis at a University in Texas

Instructor’s version - p. 19

Question 17A: How do you interpret these data?

Cases were more likely than controls to have eaten at the deli bar for lunch or dinner on March

9 (11 and six times more likely, respectively) or lunch on March 10 (8 times more likely). Cases

were not more likely than controls to have eaten at the deli bar for dinner on March 10. The

differences were statistically significant for lunch on March 9 and lunch on March 10. Fifty-six

percent of cases were exposed to the deli bar during at least one of the implicated meals.

NOTE: (OPTIONAL) More advanced students may be interested in the matched analyses. 

Matched odds ratios are based on the pairs for which cases and controls are discordant in their

exposure status (i.e., where the case was exposed and the control was not or where the control

was exposed and the case was not). The matched odds ratio cannot be calculated from the data

given in Table 1. If instructors would like to pursue this with their students, they should use the

data in Table 1a. 

Table 1a. Risk factors for illness in 29 case-control pairs, main cafeteria, University X, Texas, March

1998

Factor

Case exposed,

control

exposed

Case

exposed,

control

unexposed

Case

unexposed,

control

exposed

Case

unexposed,

control

unexposed

Matched

Odds Ratio

(95% CI)

Ate at deli bar -

lunch on March 9

0 11 1 16 11

(1.6-473)

Ate at deli bar -

dinner on March 9

1 6 1 19 6.0

(0.73-275)

Ate at deli bar -

lunch on March 10

0 8 1 19 8.0

(1.1-354)

Ate at deli bar - 

dinner on March 10

1 1 1 25 1.0

(0.01-79)

.
Gastroenteritis at a University in Texas

Instructor’s version - p. 20

Question 17B: What elements of this case-control study might affect the validity of the

measured association?

• selection bias - less than half of the cases reported at the time of the study (and less than

a quarter of the 125 cases ultimately reported to TDH) were included in the study. We

are not told how the 29 cases were selected, but since the study was limited to students

who could be reached at their dormitory rooms on the night before spring break, it seems

likely that the selection process may not have been random. Cases who were more

severely affected or ill later in the course of the outbreak (and, therefore, not well

enough to participate in the study) may also have been excluded from the study. These

cases may have had different exposures compared to less severely affected cases or cases

that were sick earlier in the outbreak. The impact of this potential selection bias on the

resulting odds ratio cannot be determined.

• possible overmatching - university roommates often share exposures. Many eat meals

together and attend special functions together. As a result, case-control roommates are

more likely to be similar (i.e., concordant) with respect to exposures compared with

other case-control pairs, and will ultimately not contribute to the analysis in a matched

study design (i.e. a matched analysis focuses on discordant pairs). This will weaken the

association between an exposure and illness (i.e., decrease the estimated odds ratio).

• matching on a possible risk factor - diarrheal diseases can be spread by person-toperson transmission. Although unlikely to be the predominant mode of transmission in

this outbreak (based on earlier information), matching of well and ill roommates will

inhibit examination of this risk factor.

Eating at the main cafeteria, in general, was not associated with illness; however eating from the

deli bar during lunch on March 9 or March 10 was significantly associated with illness. Because

such a small number of controls ate at the deli bar, individual food items from the deli bar could

not be examined.
Gastroenteritis at a University in Texas

Instructor’s version - p. 21

PART VI - DESIGNING AN EPIDEMIOLOGIC STUDY TO REFINE THE

HYPOTHESIS (STUDY #2)

By March 13, one hundred and twenty-five persons with vomiting or diarrhea had been reported

to TDH. TDH invited staff from the Centers for Disease Control and Prevention (CDC) to

participate in the ongoing investigation. CDC staff suggested submission of fresh stool

specimens from ill students for viral studies including reverse transcriptase-polymerase chain

reaction (RT-PCR). TDH and CDC staff decided to undertake an unmatched case-control study

to further explore the source of the outbreak.

Question 18: Who should be enrolled as subjects for this study?

At this point, the study hypothesis shifts to the source of the outbreak being at the main

cafeteria/deli bar. To zero in on risk factors in this setting, subjects should be persons who ate

at these facilities during the implicated time period.

The case-control study was undertaken among students who ate at the main cafeteria. A case

was defined as vomiting or diarrhea ($3 loose bowel movements during a 24-hour period) with

onset on or after March 5, 1998, in a student who was a member of the university meal plan. 

Cases were selected from those reported to TDH by one of the local emergency rooms or the

Student Health Center. Controls were students enrolled in the university meal plan who did not

have nausea, vomiting, or diarrhea since March 5.

Forty cases were randomly selected from the 125 reported through March 13. One hundred and

sixty controls were randomly selected from the university meal plan database.

Question 19: Investigators considered collecting information for the case-control study through

face-to-face interviews, telephone interviews, or self-administered questionnaires. What are the

advantages and disadvantages of each method of data collection? Which method would you

recommend given the circumstances around the outbreak?

FACE-TO-FACE

advantages: results in higher response rates than telephone or self-administered

questionnaires; can use more complex questionnaire designs (with skip patterns); usually results

in more accurate recording of responses

disadvantages: requires tracking down subjects and arranging meetings; seems less anonymous

to subjects than self-administered questionnaires; subjects may be less honest in their responses

and try to give answers they think the interviewer wishes to hear; has potential for interviewer

bias; is most costly of three (particularly if subjects are geographically dispersed)
Gastroenteritis at a University in Texas

Instructor’s version - p. 22

TELEPHONE INTERVIEW

advantages: can track down subjects more quickly than face-to-face or self-administered

questionnaires; usually results in higher response rates than self-administered questionnaires;

can use more complex questionnaire designs (with skip patterns); results in more accurate

recording of responses; is less costly than face-to-face interviews

disadvantages: seems less anonymous to subjects than self-administered questionnaires;

subjects may be less honest in their responses and try to give answers they think the interviewer

wishes to hear; has potential for interviewer bias; is more costly than self-administered

questionnaires

SELF-ADMINISTERED QUESTIONNAIRE

advantages: seems more anonymous to subjects; subjects may be more honest in their responses;

takes less investigator time once questionnaires are received by subjects; is less expensive than

face-to-face or telephone interviews

disadvantages: greater care needs to be taken in developing questionnaire so that it is selfexplanatory and easily completed by subject; additional time is necessary to send questionnaires

to students and wait for return of responses; usually results in more errors in recording of

responses; results in lower response rates

Due to spring break, a telephone interview seems to be the best method for tracking down

subjects and administering the questionnaire.

The investigators administered the study questionnaire by telephone from March 15-23. 

Students selected for participation were called at their dormitory room or their home telephone

number as recorded in university records. If the student was not present at either location but

information on his/her whereabouts was available, additional phone calls were made to contact

the student. Students not reached during spring break were interviewed on their return to the

university. 

Thirty-six cases and 144 controls were contacted. Cases included in the study were similar to all

cases with respect to gender, age, and year in college. Their dates of onset of illness had a

distribution similar to that seen in Figure 1. 
Gastroenteritis at a University in Texas

Instructor’s version - p. 23

Results from the unmatched case-control study were tabulated by TDH and CDC

epidemiologists. Only persons who ate at the main cafeteria for the specified period were

included in the meal-specific analyses. (Table 2)

Table 2. Risk factors for illness among persons eating at the main cafeteria, unmatched case-control

study, University X, Texas, March 9-10, 1998.

Exposure

Ill exposed/

Total ill 

Well exposed/

Total we ll

Measure of

association p-value

Ate at salad bar -

lunch March 9

9/30 36/100

Ate at salad bar -

dinner March 9

5/18 15/59

Ate at salad bar -

lunch March 10

6/28 23/96

Ate at salad bar -

dinner March 10

6/15 12/44

Ate at salad bar* 13/19 49/69

Ate at deli bar - 

lunch March 9

18/30 12/101

Ate at deli bar - 

dinner March 9

7/18 5/61

Ate at deli bar - 

lunch March 10

13/29 12/96

Ate at deli bar - 

dinner March 10

4/16 4/44

Ate at deli bar* 28/36 20/116

*for lunch or dinner March 9 or lunch March 10

Question 20: Calculate the appropriate measure of association for these exposures. Interpret the

results.

For a case-control study, the odds ratio is the appropriate measure of association. The odds

ratio compares the odds of exposure among cases to the odds of exposure among controls.
Gastroenteritis at a University in Texas

Instructor’s version - p. 24

Case Control TOTAL

Exposed a b (a+b)

Unexposed c d (c+d)

TOTAL (a+c) (b+d) t

 odds of exposure (cases) = number of cases with the exposure = a/c

number of cases without the exposure

 odds of exposure (controls) = number of controls with the exposure = b/d

number of controls without the exposure

odds ratio = odds of exposure (cases)

odds of exposure (controls)

= a/c

b/d

= ad/bc (known as the cross-product)

NOTE: 

An odds ratio of 1.0 means that the odds of exposure among cases is the same as the odds of

exposure among controls (i.e., the exposure is not associated with the disease).

An odds ratio of greater than 1.0 means that the odds of exposure among cases is greater than

the odds of exposure among controls; the exposure may be associated with the disease if the

odds ratio is statistically significantly greater than 1.0. A p-value of less than 0.05 or a 95%

confidence interval for the odds ratio that does not include 1.0 suggest that the odds ratio is

significantly greater than 1.0.

An odds ratio of less than 1.0 means that the odds of exposure among cases is lower than the

odds of exposure among controls; the exposure may be protective if the odds ratio is statistically

significantly less than 1.0. A p-value of less than 0.05 or a 95% confidence interval for the odds

ratio that does not include 1.0 suggest that the odds ratio is significantly less than 1.0.

To save time, the instructor may wish to divide up the calculations among different students or

groups. For example, the instructor could ask half of the class to do the calculations for
Gastroenteritis at a University in Texas

Instructor’s version - p. 25

exposure to the salad bar and the other half, the calculations for exposure to the deli bar. The

odds ratios for the exposures at the main cafeteria were:

Table 2. Risk factors for illness among persons eating at the main cafeteria, unmatched case-control

study, University X, Texas, March 9-10, 1998.

Exposure Ill exposed/

Total ill (%)

Well exposed/ Total

well (%) Odds ra tio p-value**

Ate at salad bar -

lunch March 9

9/30 (30) 36/100 (36) 0.8 0.7

Ate at salad bar -

dinner March 9

5/18 (28) 15/59 (25) 1.1 1.0

Ate at salad bar -

lunch March 10

6/28 (21) 23/96 (24) 0.9 1.0

Ate at salad bar -

dinner March 10

6/15 (40) 12/44 (27) 1.8 0.5

Ate at the salad bar* 13/19 (68) 49/69 (71) 0.9 0.9

Ate at deli bar -

 lunch March 9

18/30 (60) 12/101 (12) 11.1 <0.00001

Ate at deli bar -

dinner March 9

7/18 (39) 5/61 (8) 7.1 0.004

Ate at deli bar - 

lunch March 10

13/29 (45) 12/96 (13) 5.7 0.004

Ate at deli bar -

dinner March 10

4/16 (25) 4/44 (9) 3.3 0.2

Ate at deli bar* 28/36 (78) 20/116 (17) 16.8 <0.00001

*for lunch or dinner March 9 or lunch March 10

** p-value for 2 -tailed Fisher exact test or Yate s-corrected chi-squa re

Similar to the matched case-control study, an association was seen between illness and eating at

the main cafeteria deli bar for lunch or dinner on March 9 or lunch on March 10. Illness was

not associated with eating at the salad bar. Twenty-eight (78%) of the 36 cases reported eating

at the deli bar during at least one of the implicated meals.
Gastroenteritis at a University in Texas

Instructor’s version - p. 26

To identify the specific item(s) at the deli bar causing the outbreak, investigators reanalyzed

study data from only cases and controls who ate at the deli bar during March 9-10. (Table 3)

Table 3. Food items eaten by students who ate at deli bar during implicated meals, unmatched casecontrol study, University X, Texas, March 9-10, 1998.*

Exposure

Ill exposed/

Total ill (%)

Well exposed/

Total well (%) Odds Ratio

95% Confidence

Interval p-value

American

cheese

13/28 (46) 4/20 (20) 3.4 0.80-17.5 0.06

Swiss cheese 8/28 (29) 8/20 (40) 0.61 0.15-2.4 0.30

Ham 11/28 (39) 6/20 (30) 1.5 0.38-6.3 0.36

Turkey 15/28 (54) 11/20 (55) 0.95 0.26-3.5 0.57

Shredded lettuce 13/28 (46) 10/20 (50) 0.87 0.24-3.2 0.52

Tomato 7/28 (25) 6/20 (30) 0.78 0.18-3.5 0.50

Pickles 7/28 (25) 7/20 (35) 0.63 0.15-2.6 0.63

Mayonnaise 20/28 (71) 9/20 (45) 3.1 0.78-12.4 0.06

Mustard 10/28 (36) 9/20 (45) 0.68 0.18-2.6 0.52

*includes lunch and dinner on March 9 and lunch on March 10

Question 21: Interpret the results in Table 3.

Among persons who ate at the deli bar during the implicated meals, cases were three times more

likely than controls to eat American cheese and mayonnaise. They were also 1.5 times more

likely to have eaten ham. These differences, however, could be due to chance (p-values: 0.06 for

cheese and mayonnaise and 0.33 for ham).

The inability to epidemiologically implicate a specific food item could reflect the relatively

small number of cases included in the study or inaccurate recall of foods consumed by both

cases and controls. (Remember, some cases and controls were not questioned until their return

to campus after spring break.) These findings could also result if multiple foods were

contaminated or if illness was caused by some factor at the deli bar that was not explored.
Gastroenteritis at a University in Texas

Instructor’s version - p. 27

PART VII - ADDITIONAL INVESTIGATIONS

Water and ice samples obtained from the cafeteria on March 12 were negative for fecal

coliforms. Stool cultures and rectal swabs from the 23 foodhandlers were negative for bacteria. 

The staff member who initially refused to be interviewed worked primarily at the deli bar. 

When she finally agreed to be interviewed on March 23, she reported slicing ham on March 9,

for use at the deli bar during lunch and dinner that day, and lunch the following day. She also

prepared and served sandwiches for these same meals. She reported that she had worn gloves

while slicing the ham and while serving sandwiches at the deli bar. She denied any

gastrointestinal illness during the outbreak period but reported that her infant had been sick with

watery diarrhea since March 7, two days before she prepared items for the implicated meals. 

Because the foodhandler wore gloves during food preparation and serving, she did not feel that

handwashing was an important activity.

Of the 18 fresh stool specimens sent on ill students to CDC, 9 (50%) had evidence of Norwalklike virus (NLV) by RT-PCR. Of the four deli foods available from the implicated meals, only

the ham sample, from March 9, was positive by RT-PCR for the presence of NLV RNA. NLV

was also detected by RT-PCR in a stool sample from the ill infant of the foodhandler who

prepared the deli sandwiches on March 9. The sequence of the amplified product was identical

to those products from the ill students and the deli ham.

Question 22: Do you think the evidence implicates the foodhandler as the source of the

outbreak? Explain.

Yes. Although foodhandlers are often victims of foodborne disease outbreaks because they

consume the contaminated food themselves, the facts in this outbreak suggest this foodhandler

might have been the source of infection for the students:

• The diarrheal illness in her child preceded the outbreak and occurred at the probable

time the students were exposed (i.e., began three days before the outbreak and continued

through March 23). 

• The foodhandler prepared ingredients and sandwiches served at the deli bar during the

time that her child was ill. 

• Finally, NLV was isolated from the child’s stool and was identical to that obtained from

ill students and the deli ham.

However, the facts do not necessarily imply that the foodhandler was either ill or infected; she

may have transferred contamination from her ill infant indirectly.
Gastroenteritis at a University in Texas

Instructor’s version - p. 28

PART VIII - CONTROL

Spring break at the university ended on March 23. The chief of the campus food service called

TDH to find out what must be done to reopen the deli bar. 

Question 23: Which of the following actions would you recommend? What are the pros and

cons of each?

A) throw away all leftover deli bar foods and ingredients

B) clean and disinfect all equipment and surfaces in the deli bar

C) require all foodhandlers to submit a stool specimen before allowing them to return to

work

D) educate foodhandlers on proper foodhandling procedures including handwashing and

appropriate hot-holding and cold-holding temperatures

E) develop a sick foodhandlers policy

At this point, one must consider short-term interventions for the control of the current outbreak

and longer-term interventions which might prevent the spread of foodborne diseases at the

cafeteria in the future. The first two items on the above list will prevent further spread of

disease from this particular outbreak. The last two are more focused on prevention of future

outbreaks, although they may be effective in controlling the current outbreak if any

foodhandlers are infected and still shedding virus. It is likely that a combination of these

actions will be most appropriate to improve food safety at the university cafeteria. Examination

of stool specimens from foodhandlers (to look for viral pathogens) will be expensive and has

little benefit for the current outbreak or in preventing future problems. 

NOTE: A fundamental problem in this outbreak appeared to be the management of the deli bar

and assurance that food is safely handled on a routine basis. Although one might initially

evaluate the adequacy of specific foodhandling policies and behaviors, one must also consider

the institution’s responsibility to assure that recommended policies and practices are followed. 

Because foodworker turnover in this setting is likely to be high, the institution needs to take a

major role in assuring:

• a safe, clean environment with adequately functioning equipment 

• facilities which promote good foodhandling practices (e.g., conveniently placed sinks

with adequate soap and clean towels)

• safe sources for foods and ingredients

• training of employees in proper foodhandling procedures

• monitoring (and correction) of employee practices and behaviors
Gastroenteritis at a University in Texas

Instructor’s version - p. 29

If this assurance function seems inadequate, the university should be asked to develop a plan to

address and exercise this function. 

The health department should monitor the situation until satisfied that a safe foodhandling

system has been established. A food safety specialist and/or sanitarian should return to the

university cafeteria in one month and on a quarterly basis for at least the first year to make sure

no further disease is occurring and assess the development and implementation of appropriate

policies, the practice of good foodhandling procedures by employees, and ongoing oversight by

the institution, itself.

Question 24: Who might you consult in developing actions/policies for the campus food service

to prevent a recurrence of this problem in the future? Why?

• university administrators or their representatives - they will be legally responsible for

the policy and dealing with union or employee grievances; they must serve the assurance

function 

• supervisors in the cafeteria - they will have to implement the policy and answer

employee questions

• foodhandlers - they can provide their perspectives and insights (including hardships

resulting from the policy); they can also help review the policy and provide feedback on

ability to be understood by other employees 

• union representatives (if applicable) - they can provide information on legal implications

• staff from the local health department - they can provide expertise on foodborne diseases

and control measures; they may be able to provide an objective viewpoint and moderate

discussions
Gastroenteritis at a University in Texas

Instructor’s version - APPENDICES

APPENDIX 1

 STATE DEPARTMENT OF HEALTH

Date: 03/11/97

 #: 97-076

PERSON COMPLETING INFORMATION

Name: Xavier Onassis F : ( 512) 555 - 1234

Affiliation: 9 Local BOH (town): ______________ : State DPH (division): Epi 9

Other:_____________

REPORTER / COMPLAINANT

Name: Refused to provide F : ( ) _______ - ___________

Affiliation: : Consumer specify: 

 9 Laboratory division, ___________________________________________

 9 Local BOH facility,

 9 Medical Provider address, ____________________________________________

 9 State DPH town, etc.

 9 Other ____________________________________________

ILLNESS INFORMATION

# Persons ill: 2 

Symptoms: (% reporting)

: Diarrhea (both) : Vomiting (both) : Nausea (both) 9 Abdominal cramps 

: Fever (only one) 9 Bloody stool : Headache (only one) 9 Muscle aches

9 Chills 9 Loss of appetite : Fatigue (both) 9 Dizziness

9 Burning in mouth 9 Other symptoms: None 

Onset: Earliest Date: 03/10/97 Time: 11:30 9 AM :PM

 Latest (if $ 2 ill) Date: 03/11/97 Time: 2:30 : AM 9 PM

Duration: 9 Less than 24 Hours 9 24-48 Hours 9 More than 48 Hours : Ongoin g 9 Unknown

Ill Persons: Age

 Name Address/Town F (yrs) Occupation Med. Provider/ F

1 : same as reporter University X refused 18 student none

2 refused University X refused 19 student none

3

4

Medic al attention received (by anyone)? 9 Yes : No 9 Unknown Y If Yes, specify above: 

Stool specimens submitted (by anyone)? 9 Yes : No 9 Unknown Y To SLI 1

? 9 Yes 9 No 9

Unknown

Medical diagnosis reported?

Foodborne Illness Complaint Worksheet
Gastroenteritis at a University in Texas

Instructor’s version - APPENDICES

FOOD HISTORY

Y Obtain history back 72 hours prior to symptoms, or, if organism identified, use min and ma x incubation periods

(see p.3)

Y If $2 ill, follow above time frame for common meals (foods) only 

 # Restaurant / store where

 Date & Time 2

 Exp3

 Food(s) consumed purchased (name, town) Place consumed

 9B

March 8 9 L

 9 D

Univers ity cafeteria 9 Same (as left) 

9 Home

9 Other (specify):

 9 B

March 9 9 L

 9

Univers ity cafeteria 9 Same (as left) 

9 Home

9 Other (specify):

 9 B

March 10 9 L

 :

Anchovy pizz a and beer Local pizzeria 9 Same (as left) 

9 Home

: Other (specify):

 9 B

 9 L

 9

9 Same (as left) 

9 Home

9 Other (specify):

 9 B

 9 L

 9 D

9 Same (as left) 

9 Home

9 Other (specify):

 9 B

 9 L

 9 D

9 Same (as left) 

9 Home

9 Other (specify):

NOTES

Student refused to provide food history beyond foods eaten at local pizzeria. He reported that he and his roommate

shared no other meals in the last 72 hours; they ate separately at the University cafeteria.
Gastroenteritis at a University in Texas

Instructor’s version - APPENDICES

FOOD TESTING

Food(s) available for testing? 9 Yes 9 No : Unknown Sent to SLI 1? 9 Yes 9 No 9 Unknown

If Yes, specify food(s) & sources:

Product and Manufacturer Information for Commercially-Processed Food(s)

Product name: ____________________________________________ Code/lot #______________________

Expiration date: _____ /_____ /_____ Package size/type: ________________________________________

Manufacturer: __________________________________________________ F: ( ) ______ - __________

Address: 

Incubation Periods for Selected Organisms

 Min Max Min Max Min Max

B. cereus (short) 1 hr 6 hrs E. coli O157:H7 3 days 8 Staph. aureus 30 min 8 hrs

B. cereus (long) 6 hrs 24 hrs Hepatitis A 15 days 50 days Shigella 12 hrs 96 hrs

Campylobacter 1 day 10 days Salmonella (non-typhi) 6 hrs 5 days Vibrio cholerae few hrs 5 days

Cyclospora 1 day 14 days Salmonella typh i 1 wk 3 wks Viral GI 12 hrs 48 hrs

C. perfringens 6 hrs 24 hrs Shellfish poisoning min few hrs Yersinia 3 days 7 days

1 State L abora tory Institute

2 Always record Time if possible; otherwise, choose B=brea kfast, L=lunc h, D=dinner 

3 Total # perso ns (both ill and well) wh o consu med in dicated f ood(s)
Gastroenteritis at a University in Texas

Instructor’s version - APPENDICES

APPENDIX 2. Causative agents for acute enteric illness

INFECTIOUS

Bacteria

Aeromonas (not proven)

Bacillus cereus

Campylobacter 

Clostridium perfringens

Escherichia coli

 Shiga Toxin producing E. coli (STEC)

 Enterotoxin producing E. coli (ETEC)

 Enteroinvasive E. coli (EIEC)

 Enteropathogenic E. coli (EPEC)

Plesiomonas (not proven)

Salmonella, non-typhoid

Salmonella Typhi

Shigella

Vibrio

Yersinia enterocolitica

Viruses

Norwalk and Norwalk-like agents (caliciviruses) 

Rotavirus

Hepatitis A

Parasites

Cryptosporidium parvum

Cyclospora

Entamoeba histolytica

Giardia lamblia

TOXINS

Bacillus cereus

Staphylococcus aureus

Clostridium perfringens

Clostridium botulinum

heavy metals (cadmium, copper, zinc, tin)

mushroom toxins

fish and shellfish toxins (scombroid,

ciguatera)

insecticides

drugs

boric acid

OTHER

psychogenic

radiation
Gastroenteritis at a University in Texas

Instructor’s version - APPENDICES

APPENDIX 3. Recommendations for Collection of Stool Specimens for Laboratory

Examination (from the Morbidity and Mortality Weekly Report: Recommendations and Reports

1990;30 [No. RR-14])

Specimen collection is critical in identifying the causative agent in an outbreak of

gastroenteritis. Bacteria, viruses, and parasites each require different specimens and methods of

storage and transport for optimal diagnosis. When the causative agent is unknown, one should

consider plausible pathogens based on predominant signs and symptoms and other outbreak

information. 

For bacterial pathogens

Rectal swabs or swabs of fresh stools should be placed in refrigerated Cary-Blair transport

medium. If the specimens are likely to be examined within 48 hours after collection, they can be

refrigerated at 4°C until shipping. Specimens should be enclosed in a secure container and

placed in a waterproof bag. Specimens should be packed with ice or frozen refrigerant packs in

an insulated box.

If specimens must be held longer than 48 hours, they should be frozen as soon as possible after

collection. Although storage in an ultra-low freezer (-70°C) is preferable, storage in a hometype freezer (if it is properly set at -20°C) is acceptable for short periods. So that the specimens 

remain frozen, they should be shipped on dry ice. Sufficient dry ice should be used to keep

specimens frozen until the laboratory processes them (i.e., enough dry ice to fill one-third to onehalf of the shipping container). Glass tubes should not be in direct contact with the dry ice; a

layer of paper or other material should be placed between the tubes and the dry ice. To prevent

excess exposure to carbon dioxide (from the dry ice), screw caps should be tightened and sealed

with electrical tape or specimens should be sealed in a plastic bag within the container of dry

ice.

For viral pathogens

Collect as large a quantity of diarrheal stool as can be obtained (at least 10 cc). Place in a leakproof, clean, dry container, and refrigerate immediately at 4°C. DO NOT FREEZE

SPECIMENS IF ELECTRON MICROSCOPY EXAMINATION IS ANTICIPATED. The use of

rectal swabs to detect viral causes of gastroenteritis is discouraged because the sensitivity of

detection compared to bulk stool is suspected to be low.

For parasites

Mix fresh bulk stool specimens thoroughly with each of two preservatives, 10% formalin and

polyvinyl alcohol fixative, at a ratio of one part of stool to 3 parts of preservative. If there is any

delay in obtaining the preservatives, refrigerate untreated stool specimens at 4°C for up to 48

hours. For routine microscopy, DO NOT FREEZE. Once preserved, the specimens can be stored

and transported at room temperature or refrigerated. Note, it is now possible to do genotyping

on many parasites, but this may require different preservatives. If parasites are considered a

likely etiology, contact a lab that has the capacity to conduct genetic testing and ask for specific

instructions. Currently recommended preservatives for genetic analysis include freezing the

specimen or preserving it in ethanol or potassium dichromate.