**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^    |
| Number range CHAPTERRee A. Calmes-Slovin,^5^ Dana Cotton,^6^ Charlie  |
| Horton,^6^ Sandra G. Ford,^6^ Pam Patterson^6^                        |
|                                                                       |
| ^1^Centers for Disease Control and Prevention, ^2^Texas Department of |
| Health, ^3^Baylor College of Medicine, ^4^Atlanta Veterans            |
| Administration Medical Center, ^5^City of Huntsville, Health          |
| Inspections, ^6^Texas 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]{.underline}. 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]{.underline} Advanced
[]{.underline}

**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:]{.underline} 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:*

1.  ***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)*

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1.  ***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)?*

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1.  ***WHEN** did the affected person(s) become ill?*

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1.  ***WHERE** are the affected persons located? (including names and
    telephone numbers)*

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1.  ***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.*

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:]{.underline} 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:]{.underline} 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:*

1.  *an outbreak associated with a commercially distributed food
    product*

2.  *severe (life-threatening) illnesses such botulism or [E.
    coli]{.underline} O157:H7 infection*

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1.  *confirmed clusters of a similar illness that appear to be
    associated with a specific food preparer or food service
    establishment*

2.  *instances where a large number of people appear to be affected*

3.  *indications of adulterated food presenting an imminent danger*

4.  *foodborne illness in a foodhandler*

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

6.  *signs and symptoms (or confirmed diagnoses) among affected
    individuals suggesting they might not have the same illness*

7.  *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*

8.  *confirmed diagnosis and/or clinical symptoms that are not
    consistent with the foods eaten and the onset of illness*

9.  *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.

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:]{.underline} 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".*

**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:]{.underline} 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:*

6.  *[Infections]{.underline} 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.*

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6.  *[Intoxications]{.underline} 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.*

[Question 6:]{.underline} 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:*

6.  *predominant signs and symptoms*

7.  *incubation period*

8.  *duration of symptoms*

9.  *suspect food*

10. *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:]{.underline} 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:*

6.  *patient's name or identification number - used to track and provide
    results; allows comparison of results from repeat specimens*

7.  *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)*

8.  *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)*

9.  *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]{.underline} O157:H7 or other
    Shiga-like toxin producing [E. coli]{.underline})*

[Question 8:]{.underline} 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]{.underline}*

*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 home-type 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]{.underline}*

*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]{.underline}*

*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.*

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:]{.underline} How might you interpret the bacterial culture
results? What questions do these results raise?

*Several explanations may exist for the negative cultures:*

6.  *Specimens may have been mishandled during storage or transport
    leading to the death of any biological pathogen present.*

7.  *Specimens may have been mishandled during processing or culture
    leading to the death of any biological pathogen present.*

8.  *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).*

9.  *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.*

######## 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 known for three ill students.)

![](media/image1.png){width="5.990277777777778in"
height="4.104166666666667in"}

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:]{.underline} 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:*

6.  *why it is important to investigate the outbreak (especially, to the
    university, itself) and to do so in a timely fashion*

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6.  *what has already been done and found to date*

7.  *what is planned*

8.  *what the health department can provide to the university*

9.  *what kind of cooperation will be needed from the university (food
    samples, menus, time and place to interview foodhandlers and
    managers, etc.)*

10. *how press inquiries will be handled*

11. *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:*

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

2.  *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.
>
> 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:]{.underline} 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:]{.underline} 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*

*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:]{.underline} 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:]{.underline} 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:]{.underline} 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*

[Question 12:]{.underline} What actions would you take?

*At this point, findings are only [suggestive]{.underline} 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.*

**PART IV - ENVIRONMENTAL INVESTIGATION**

Based on clinical findings, the descriptive epidemiology of early cases,
and hypothesis-generating 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:]{.underline} 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,

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:]{.underline} 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:*

1.  *the source may not be the deli bar and cases may continue to occur*

2.  *more specific information is needed on the source to determine when
    it is safe to reopen the deli bar*

3.  *more specific information is needed on the source to prevent the
    problem from recurring in the future*

**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:]{.underline} 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 case-control study would be the most cost-effective study type at
this juncture.*

[Question 16:]{.underline} 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       | Well       | Matched | 95%      | p-v  |
|               | exposed/  | exposed/   |         | Co       | alue |
|               |           | Total      | Odds    | nfidence |      |
|               | Total     | well\* (%) | Ra      | Interval |      |
|               | ill\* (%) |            | tio\*\* |          |      |
+---------------+-----------+------------+---------+----------+------+
| Ate at deli   | 11/28     | 1/29 (3)   | 11.0    | 1.6-473  | \<   |
| bar -         | (39)      |            |         |          | 0.01 |
|               |           |            |         |          |      |
| lunch on      |           |            |         |          |      |
| March 9       |           |            |         |          |      |
+---------------+-----------+------------+---------+----------+------+
| Ate at deli   | 7/27 (26) | 2/29 (7)   | 6.0     | 0.73-275 | 0.06 |
| bar - dinner  |           |            |         |          |      |
| on March 9    |           |            |         |          |      |
+---------------+-----------+------------+---------+----------+------+
| Ate at deli   | 8/29 (28) | 1/28 (4)   | 8.0     | 1.1-354  | 0.02 |
| bar -         |           |            |         |          |      |
|               |           |            |         |          |      |
| lunch on      |           |            |         |          |      |
| March 10      |           |            |         |          |      |
+---------------+-----------+------------+---------+----------+------+
| Ate at deli   | 2/29 (7)  | 2/28 (7)   | 1.0     | 0.01-79  | 0.75 |
| bar - dinner  |           |            |         |          |      |
| on March 10   |           |            |         |          |      |
+---------------+-----------+------------+---------+----------+------+
| Ate at deli   | 15/27     | 3/28 (11)  | 7.0     | 1        | \<   |
| bar - lunch   | (56)      |            |         | .61-63.5 | 0.01 |
| or dinner     |           |            |         |          |      |
| March 9 or    |           |            |         |          |      |
| lunch March   |           |            |         |          |      |
| 10            |           |            |         |          |      |
+---------------+-----------+------------+---------+----------+------+

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

\*\*The data provided for cases and controls cannot be used to calculate
the matched odds ratio which is based on an analysis of discordant
pairs.

[Question 17A:]{.underline} 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    | *Case    | *Case    | *Case    | *Matched |
|              | exposed, | exposed, | un       | un       | Odds     |
|              | control  | control  | exposed, | exposed, | Ratio*   |
|              | exposed* | un       | control  | control  |          |
|              |          | exposed* | exposed* | un       | *(95%    |
|              |          |          |          | exposed* | CI)*     |
+--------------+----------+----------+----------+----------+----------+
| *Ate at deli | *0*      | *11*     | *1*      | *16*     | *11*     |
| bar - lunch  |          |          |          |          |          |
| on March 9*  |          |          |          |          | *(1      |
|              |          |          |          |          | .6-473)* |
+--------------+----------+----------+----------+----------+----------+
| *Ate at deli | *1*      | *6*      | *1*      | *19*     | *6.0*    |
| bar - dinner |          |          |          |          |          |
| on March 9*  |          |          |          |          | *(0.     |
|              |          |          |          |          | 73-275)* |
+--------------+----------+----------+----------+----------+----------+
| *Ate at deli | *0*      | *8*      | *1*      | *19*     | *8.0*    |
| bar - lunch  |          |          |          |          |          |
| on March 10* |          |          |          |          | *(1      |
|              |          |          |          |          | .1-354)* |
+--------------+----------+----------+----------+----------+----------+
| *Ate at deli | *1*      | *1*      | *1*      | *25*     | *1.0*    |
| bar -*       |          |          |          |          |          |
|              |          |          |          |          | *(0      |
| *dinner on   |          |          |          |          | .01-79)* |
| March 10*    |          |          |          |          |          |
+--------------+----------+----------+----------+----------+----------+

*.*

[Question 17B:]{.underline} What elements of this case-control study
might affect the validity of the measured association?

1.  *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.*

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1.  *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).*

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1.  *matching on a possible risk factor - diarrheal diseases can be
    spread by person-to-person transmission. Although
    [unlikely]{.underline} 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.

**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:]{.underline} 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:]{.underline} 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:]{.underline} 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:]{.underline} 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)*

*TELEPHONE INTERVIEW*

*[advantages:]{.underline} 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:]{.underline} 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:]{.underline} 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:]{.underline} greater care needs to be taken in
developing questionnaire so that it is self-explanatory 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.

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         | Well         | Measure of | p-value  |
|                | exposed/    | exposed/     | a          |          |
|                |             | Total well   | ssociation |          |
|                | Total ill   |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at salad   | 9/30        | 36/100       |            |          |
| bar - lunch    |             |              |            |          |
| March 9        |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at salad   | 5/18        | 15/59        |            |          |
| bar - dinner   |             |              |            |          |
| March 9        |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at salad   | 6/28        | 23/96        |            |          |
| bar - lunch    |             |              |            |          |
| March 10       |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at salad   | 6/15        | 12/44        |            |          |
| bar - dinner   |             |              |            |          |
| March 10       |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at salad   | 13/19       | 49/69        |            |          |
| bar\*          |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at deli    | 18/30       | 12/101       |            |          |
| bar -          |             |              |            |          |
|                |             |              |            |          |
| lunch March 9  |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at deli    | 7/18        | 5/61         |            |          |
| bar -          |             |              |            |          |
|                |             |              |            |          |
| dinner March 9 |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at deli    | 13/29       | 12/96        |            |          |
| bar -          |             |              |            |          |
|                |             |              |            |          |
| lunch March 10 |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at deli    | 4/16        | 4/44         |            |          |
| bar -          |             |              |            |          |
|                |             |              |            |          |
| dinner March   |             |              |            |          |
| 10             |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| Ate at deli    | 28/36       | 20/116       |            |          |
| bar\*          |             |              |            |          |
+----------------+-------------+--------------+------------+----------+

\*for lunch or dinner March 9 or lunch March 10

[Question 20:]{.underline} 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.*

  ------------- ------------ ------------ --------------------------------
                *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]{.underline} = a/c*

*number of cases without the exposure*

*odds of exposure (controls) = [number of controls with the
exposure]{.underline} = b/d*

*number of controls without the exposure*

*odds ratio = [odds of exposure (cases)]{.underline}*

*odds of exposure (controls)*

*= [a/c]{.underline}*

*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 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        | *Well        | *Odds      | *p-va    |
|                | exposed/*   | exposed/     | ratio*     | lue\*\** |
|                |             | Total well   |            |          |
|                | *Total ill  | (%)*         |            |          |
|                | (%)*        |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at salad  | *9/30 (30)* | *36/100      | *0.8*      | *0.7*    |
| bar --*        |             | (36)*        |            |          |
|                |             |              |            |          |
| *lunch March   |             |              |            |          |
| 9*             |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at salad  | *5/18 (28)* | *15/59 (25)* | *1.1*      | *1.0*    |
| bar -- dinner  |             |              |            |          |
| March 9*       |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at salad  | *6/28 (21)* | *23/96 (24)* | *0.9*      | *1.0*    |
| bar -- lunch   |             |              |            |          |
| March 10*      |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at salad  | *6/15 (40)* | *12/44 (27)* | *1.8*      | *0.5*    |
| bar -- dinner  |             |              |            |          |
| March 10*      |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at the    | *13/19      | *49/69 (71)* | *0.9*      | *0.9*    |
| salad bar\**   | (68)*       |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at deli   | *18/30      | *12/101      | *11.1*     | *\<      |
| bar --*        | (60)*       | (12)*        |            | 0.00001* |
|                |             |              |            |          |
| *lunch March   |             |              |            |          |
| 9*             |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at deli   | *7/18 (39)* | *5/61 (8)*   | *7.1*      | *0.004*  |
| bar --*        |             |              |            |          |
|                |             |              |            |          |
| *dinner March  |             |              |            |          |
| 9*             |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at deli   | *13/29      | *12/96 (13)* | *5.7*      | *0.004*  |
| bar --*        | (45)*       |              |            |          |
|                |             |              |            |          |
| *lunch March   |             |              |            |          |
| 10*            |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at deli   | *4/16 (25)* | *4/44 (9)*   | *3.3*      | *0.2*    |
| bar --*        |             |              |            |          |
|                |             |              |            |          |
| *dinner March  |             |              |            |          |
| 10*            |             |              |            |          |
+----------------+-------------+--------------+------------+----------+
| *Ate at deli   | *28/36      | *20/116      | *16.8*     | *\<      |
| bar\**         | (78)*       | (17)*        |            | 0.00001* |
+----------------+-------------+--------------+------------+----------+

*\*for lunch or dinner March 9 or lunch March 10*

*\*\* p-value for 2-tailed Fisher exact test or Yates-corrected
chi-square*

*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.*

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 case-control study, University X, Texas,
March 9-10, 1998.\*

+------------+----------+------------+---------+-------------+-------+
| Exposure   | Ill      | Well       | Odds    | 95%         | p-    |
|            | exposed/ | exposed/   | Ratio   | Confidence  | value |
|            |          | Total well |         | Interval    |       |
|            | Total    | (%)        |         |             |       |
|            | ill (%)  |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| American   | 13/28    | 4/20 (20)  | 3.4     | 0.80-17.5   | 0.06  |
| cheese     | (46)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Swiss      | 8/28     | 8/20 (40)  | 0.61    | 0.15-2.4    | 0.30  |
| cheese     | (29)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Ham        | 11/28    | 6/20 (30)  | 1.5     | 0.38-6.3    | 0.36  |
|            | (39)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Turkey     | 15/28    | 11/20 (55) | 0.95    | 0.26-3.5    | 0.57  |
|            | (54)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Shredded   | 13/28    | 10/20 (50) | 0.87    | 0.24-3.2    | 0.52  |
| lettuce    | (46)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Tomato     | 7/28     | 6/20 (30)  | 0.78    | 0.18-3.5    | 0.50  |
|            | (25)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Pickles    | 7/28     | 7/20 (35)  | 0.63    | 0.15-2.6    | 0.63  |
|            | (25)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Mayonnaise | 20/28    | 9/20 (45)  | 3.1     | 0.78-12.4   | 0.06  |
|            | (71)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+
| Mustard    | 10/28    | 9/20 (45)  | 0.68    | 0.18-2.6    | 0.52  |
|            | (36)     |            |         |             |       |
+------------+----------+------------+---------+-------------+-------+

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

[Question 21:]{.underline} 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.*

**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 Norwalk-like 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:]{.underline} 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:*

1.  *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).*

2.  *The foodhandler prepared ingredients and sandwiches served at the
    deli bar during the time that her child was ill.*

3.  *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.*

**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:]{.underline} 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:*

2.  *a safe, clean environment with adequately functioning equipment*

3.  *facilities which promote good foodhandling practices (e.g.,
    conveniently placed sinks with adequate soap and clean towels)*

4.  *safe sources for foods and ingredients*

5.  *training of employees in proper foodhandling procedures*

6.  *monitoring (and correction) of employee practices and behaviors*

*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:]{.underline} Who might you consult in developing
actions/policies for the campus food service to prevent a recurrence of
this problem in the future? Why?

2.  *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*

3.  *supervisors in the cafeteria - they will have to implement the
    policy and answer employee questions*

4.  *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*

5.  *union representatives (if applicable) - they can provide
    information on legal implications*

6.  *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*

**APPENDIX 1**

<table style="width:100%;">
<colgroup>
<col style="width: 2%" />
<col style="width: 15%" />
<col style="width: 5%" />
<col style="width: 2%" />
<col style="width: 19%" />
<col style="width: 9%" />
<col style="width: 1%" />
<col style="width: 5%" />
<col style="width: 13%" />
<col style="width: 3%" />
<col style="width: 20%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="11"><h1 id="state-department-of-health">State Department of
Health</h1>
<h2 id="foodborne-illness-complaint-worksheet">FOODBORNE ILLNESS
COMPLAINT WORKSHEET</h2></td>
</tr>
<tr class="even">
<td colspan="3"><p id="section" class="heading"></p>
<p id="section-1" class="heading"></p>
<p id="date-031197" class="heading">Date: <u>03/11/97</u></p>
<p>#: <u>97-076</u></p></td>
<td colspan="5"></td>
<td colspan="3"></td>
</tr>
<tr class="odd">
<td colspan="11"><h3 id="person-completing-information"><strong>PERSON
COMPLETING INFORMATION</strong></h3>
<p><strong>Name:</strong> <u>Xavier Onassis</u> : (512)
<u>555-1234</u></p>
<p><strong>Affiliation:</strong>  Local BOH <em>(town)</em>:
______________  State DPH <em>(division)</em>: <u>Epi</u> 
Other:_____________</p></td>
</tr>
<tr class="even">
<td colspan="11"><h3
id="reportercomplainant"><strong>REPORTER/COMPLAINANT</strong></h3>
<p><strong>Name:</strong> <u>Refused to provide</u> <strong>:</strong>
( ) _______ - ___________</p>
<p><strong>Affiliation:</strong>  Consumer
<strong><em><u>specify:</u></em> →</strong></p>
<p> Laboratory division,
____________________________________________________</p>
<p> Local BOH <em>facility,</em></p>
<p> Medical Provider address,
____________________________________________________</p>
<p> State DPH <em>town, etc.</em></p>
<p> Other ____________________________________________________</p></td>
</tr>
<tr class="odd">
<td colspan="11"><h3 id="illness-information"><strong>ILLNESS
INFORMATION</strong></h3>
<p><strong># Persons ill: 2</strong></p>
<p><strong>Symptoms:</strong> <em>(mark if reported <strong><u>for
anyone</u></strong>)<strong>:</strong></em></p>
<p> Diarrhea (both)  Vomiting (both)  Nausea (both)  Abdominal
cramps</p>
<p> Fever (only one)  Bloody stool  Headache (only one)  Muscle
aches</p>
<p> Chills  Loss of appetite  Fatigue (both)  Dizziness</p>
<p> Burning in mouth  Other symptoms: <u>None </u></p>
<p><strong>Onset: →</strong> Earliest Date: <u>03/10/97</u> Time:
<u>11:30</u> AM PM</p>
<p>Latest <strong>(if &gt; 2 ill)</strong> Date: <u>03/11/97</u> Time:
<u>2:30</u> AM PM</p>
<p><strong>Duration:</strong>  Less than 24 Hours  24-48 Hours  More
than 48 Hours  Ongoing  Unknown</p>
<p><strong>Ill Persons: Age</strong></p>
<p><strong>Name Address/Town</strong>  <strong>(yrs) Occupation Med.
Provider/</strong> </p></td>
</tr>
<tr class="even">
<td><strong>1</strong></td>
<td colspan="3"> same as reporter (above)</td>
<td>University X</td>
<td colspan="2">refused</td>
<td>18</td>
<td>student</td>
<td colspan="2">none</td>
</tr>
<tr class="odd">
<td><strong>2</strong></td>
<td colspan="3">refused</td>
<td>University X</td>
<td colspan="2">refused</td>
<td>19</td>
<td>student</td>
<td colspan="2">none</td>
</tr>
<tr class="even">
<td><strong>3</strong></td>
<td colspan="3"></td>
<td></td>
<td colspan="2"></td>
<td></td>
<td></td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td><strong>4</strong></td>
<td colspan="3"></td>
<td></td>
<td colspan="2"></td>
<td></td>
<td></td>
<td colspan="2"></td>
</tr>
<tr class="even">
<td colspan="11"><p><strong>Medical attention</strong> received
<strong><em>(<u>by anyone)</u></em>?</strong>  Yes  No  Unknown
<strong>→ <em>If Yes, specify above:</em> ↑</strong></p>
<p><strong>Stool specimens</strong> submitted <strong><em>(<u>by
anyone)</u></em>?</strong>  Yes  No  Unknown <strong>→</strong>
<strong>To SLI <sup>1</sup>?</strong>  Yes  No  Unknown</p>
<p><strong>Medical diagnosis</strong>
reported<strong>?</strong></p></td>
</tr>
<tr class="odd">
<td colspan="11"><h3 id="food-history"><strong>FOOD
HISTORY</strong></h3>
<p><strong>→</strong> Obtain history <strong><u>back 72
hours</u></strong> prior to symptoms, <strong>or</strong>, if organism
identified, <strong><u>b/n min and max incubation</u></strong> periods
(see p.2)</p>
<p><strong>→ <u>If &gt; 2 ill</u></strong>, follow above time frame for
<strong><u>common meals (foods) only</u></strong></p>
<p><strong># Restaurant / store where</strong></p>
<p><strong>Date &amp; Time<sup>2</sup> Exp<sup>3</sup> Food(s) consumed
purchased (name, town) Place consumed</strong></p></td>
</tr>
<tr class="even">
<td colspan="2"><p> B</p>
<p>March 8  L</p>
<p> D</p></td>
<td><h3 id="section-2"></h3></td>
<td colspan="3"><h3 id="university-cafeteria">University
cafeteria</h3></td>
<td colspan="4"><h3 id="section-3"></h3></td>
<td><h3 id="same-as-left"><strong> Same <em>(as left)</em></strong>
</h3>
<h3 id="home"><strong> Home</strong></h3>
<p> Other
<em>(specify<strong>)</strong></em><strong>:</strong></p></td>
</tr>
<tr class="odd">
<td colspan="2"><p> B</p>
<p>March 9  L</p>
<p> D</p></td>
<td><h3 id="section-4"></h3></td>
<td colspan="3"><h3 id="university-cafeteria-1">University
cafeteria</h3></td>
<td colspan="4"><h3 id="section-5"></h3></td>
<td><h3 id="same-as-left-1"><strong> Same <em>(as left)</em></strong>
</h3>
<h3 id="home-1"><strong> Home</strong></h3>
<p> Other
<em>(specify<strong>)</strong></em><strong>:</strong></p></td>
</tr>
<tr class="even">
<td colspan="2"><p> B</p>
<p>March 10  L</p>
<p> D</p></td>
<td><h3 id="section-6"></h3></td>
<td colspan="3"><h3 id="anchovy-pizza-and-beer">Anchovy pizza and
beer</h3></td>
<td colspan="4"><h3 id="local-pizzeria">Local pizzeria</h3></td>
<td><h3 id="same-as-left-2"><strong> Same <em>(as left)</em></strong>
</h3>
<h3 id="home-2"><strong> Home</strong></h3>
<p> Other
<em>(specify<strong>)</strong></em><strong>:</strong></p></td>
</tr>
<tr class="odd">
<td colspan="2"><p> B</p>
<p> L</p>
<p> D</p></td>
<td><h3 id="section-7"></h3></td>
<td colspan="3"><h3 id="section-8"></h3></td>
<td colspan="4"><h3 id="section-9"></h3></td>
<td><h3 id="same-as-left-3"><strong> Same <em>(as left)</em></strong>
</h3>
<h3 id="home-3"><strong> Home</strong></h3>
<p> Other
<em>(specify<strong>)</strong></em><strong>:</strong></p></td>
</tr>
<tr class="even">
<td colspan="2"><p> B</p>
<p> L</p>
<p> D</p></td>
<td><h3 id="section-10"></h3></td>
<td colspan="3"><h3 id="section-11"></h3></td>
<td colspan="4"><h3 id="section-12"></h3></td>
<td><h3 id="same-as-left-4"><strong> Same <em>(as left)</em></strong>
</h3>
<h3 id="home-4"><strong> Home</strong></h3>
<p> Other
<em>(specify<strong>)</strong></em><strong>:</strong></p></td>
</tr>
<tr class="odd">
<td colspan="2"><p> B</p>
<p> L</p>
<p> D</p></td>
<td><h3 id="section-13"></h3></td>
<td colspan="3"><h3 id="section-14"></h3></td>
<td colspan="4"><h3 id="section-15"></h3></td>
<td><h3 id="same-as-left-5"><strong> Same <em>(as left)</em></strong>
</h3>
<h3 id="home-5"><strong> Home</strong></h3>
<p> Other
<em>(specify<strong>)</strong></em><strong>:</strong></p></td>
</tr>
<tr class="even">
<td colspan="11"><h3 id="section-16"></h3>
<h3 id="notes"><strong>NOTES</strong></h3>
<p>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.</p></td>
</tr>
</tbody>
</table>

+-----------------------+-----------------------+----------------------+
| ###  {#section-17}    |                       |                      |
|                       |                       |                      |
| ### **FOOD TESTING**  |                       |                      |
|                       |                       |                      |
| **Food(s)** available |                       |                      |
| for testing?  Yes   |                       |                      |
| No  Unknown **→**    |                       |                      |
| **Sent to SLI ^1^?**  |                       |                      |
|  Yes  No  Unknown  |                       |                      |
|                       |                       |                      |
| → ***If Yes,          |                       |                      |
| specify** food(s) &   |                       |                      |
| sources*:             |                       |                      |
+-----------------------+-----------------------+----------------------+
| ###  {#section-18}    |                       |                      |
|                       |                       |                      |
| **Product and         |                       |                      |
| Manufacturer          |                       |                      |
| Information for       |                       |                      |
| C                     |                       |                      |
| ommercially-Processed |                       |                      |
| Food(s)**             |                       |                      |
|                       |                       |                      |
| Product name:         |                       |                      |
| \_\_\_                |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| Code/lot              |                       |                      |
| #\_                   |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
|                       |                       |                      |
| Expiration date:      |                       |                      |
| \_\_\_\_\_            |                       |                      |
| /\_\_\_\_\_           |                       |                      |
| /\_\_\_\_\_ Package   |                       |                      |
| size/type:            |                       |                      |
| \_\_\_\_\_\_\_\_\_\   |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
|                       |                       |                      |
| Manufacturer:         |                       |                      |
| \_\_\_                |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| \_\_\_\_\_\_\_\_\_\_\ |                       |                      |
| _\_\_\_\_\_\_\_\_\_\_ |                       |                      |
| : ( ) \_\_\_\_\_\_ - |                       |                      |
| \_\_\_\_\_\_\_\_\_\_  |                       |                      |
|                       |                       |                      |
| Address:              |                       |                      |
+-----------------------+-----------------------+----------------------+
| ###  {#section-19}    |                       |                      |
|                       |                       |                      |
| ### **I               |                       |                      |
| ncubation Periods for |                       |                      |
|  Selected Organisms** |                       |                      |
|                       |                       |                      |
| ######  **Min         |                       |                      |
| Max Min Max Min Max** |                       |                      |
+-----------------------+-----------------------+----------------------+
| ### B. cere           | ### E. coli           | ### Staph.           |
| us (short) 1 hr 6 hrs | O157:H7 3 days 8 days |  aureus 30 min 8 hrs |
+-----------------------+-----------------------+----------------------+
| B. cereus (long) 6    | Hepatitis A 15 days   | Shigella 12 hrs 96   |
| hrs 24 hrs            | 50 days 15-50 days    | hrs                  |
+-----------------------+-----------------------+----------------------+
| Campylobacter 1 day   | Salmonella            | Vibrio cholerae few  |
| 10 days               | (non-typhi) 6 hrs 72  | hrs 5 days           |
|                       | hrs 12-36 hrs         |                      |
+-----------------------+-----------------------+----------------------+
| Cyclospora 1 day 14   | Salmonella typhi 1 wk | Viral GI 12 hrs 48   |
| days 6-8 days         | 3 wks 1-3 weeks       | hrs                  |
+-----------------------+-----------------------+----------------------+
| C. perfringens 6 hrs  | Shellfish poisoning   | Yersinia 3 days 7    |
| 24 hrs 6-24 hrs       | minutes few hrs \<1   | days                 |
|                       | hr                    |                      |
+-----------------------+-----------------------+----------------------+

**1** State Laboratory Institute

**2** Always record **Time** if possible; otherwise, choose
**B**=breakfast, **L**=lunch, **D**=dinner

**3** Total \# persons (both ill and well) who consumed indicated
food(s)

**APPENDIX 2.** Causative agents for acute enteric illness

INFECTIOUS

[Bacteria]{.underline}

*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]{.underline}

Norwalk and Norwalk-like agents

(caliciviruses)

Rotavirus

Hepatitis A

[Parasites]{.underline}

*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

**APPENDIX 3.** Recommendations for Collection of Stool Specimens for
Laboratory Examination *(from the [Morbidity and Mortality Weekly
Report: Recommendations and Reports]{.underline} 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]{.underline}

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 home-type 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 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]{.underline}

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]{.underline}

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.