Gastroenteritis at a University in Texas (Epi-Ready)

Instructor’s version – p. 1

Gastroenteritis at a University in Texas

Epi-Ready Course

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,1Ree A. Calmes-Slovin,5 Dana Cotton,6 Charlie Horton,6 Sandra G. Ford,6 Pam Patterson6
1Centers for Disease Control and Prevention, 2Texas Department of Health, 3Baylor College of Medicine, 4Atlanta Veterans Administration Medical Center, 5City of Huntsville, Health Inspections, 6Texas Department of Health, Region 6/5S
Case study and instructor’s guide created by: Jeanette K. Stehr-Green, MD

NOTE: This case study is based on a real-life outbreak investigation undertaken in Texas in 1998. Some aspects of the original outbreak and investigation have been altered, however, to assist in meeting the desired teaching objectives and allow completion of the case study in less than 1.5 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.

Please send us your comments on this case study by visiting our website at Please include the name of the case study with your comments.

April 2012

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Public Health Service

Centers for Disease Control and Prevention

Atlanta, Georgia 30333

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 complainants who report a possible foodborne illness to the health department.
  2. Prioritize the investigation of a suspected foodborne illnessor foodborne disease outbreak.
  3. Listclues that might help determine the causative agent in an outbreak of acute gastrointestinal illness.
  4. Use the descriptive epidemiology among cases, information about the setting in which the outbreak has occurred, and the results of hypothesis-generating interviews to develop hypotheses about the source of an outbreak.
  5. Discusssome of the issues associated with the collectionof clinical specimens for the investigation of a suspected foodborne disease outbreak.
  6. List key areas of focus in investigating a facility implicated in a foodborne disease outbreak including interviews with food workers, observation of kitchen practices, and collection of samples.
  7. Interpret the measure of association for a case-control study.

PART I - OUTBREAK DETECTION

On the morning of March 11, the Texas Department of Health (TDH) in Austin received a telephone call from a student at a university in south-central Texas. The student reported that he and his roommate, a fraternity brother, were suffering from nausea, vomiting, and diarrhea. Both had become ill during the night. The roommate had taken an over-the-counter medication with some relief of his symptoms. Neither the student nor his roommate had seen a physician or gone to the emergency room.

The students believed their illness was due to food they had eaten at a local pizzeria the previous night. They asked if they should attend classes and take a biology midterm exam that was scheduled that afternoon.

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

In recording a complaint about a possible foodborne illness, it is important to systematically collect the following information:

  • WHAT is the person’s problem? (e.g., clinical description of the illness, whether a physician was consulted, whether any tests were performed or any treatments were provided)
  • WHO else became ill, their characteristics (e.g., age, sex, occupation), and the nature of their illnesses (e.g., symptoms, whether any persons were hospitalized or died)?
  • WHEN did the affected person(s) become ill?
  • WHERE are the affected persons located? (including names and telephone numbers)
  • WHY (and HOW) do they think they became ill? (e.g., suspected exposures,recent exposures to food, water (drinking and recreational), ice, other ill persons, children, and animals)

NOTE TO INSTRUCTOR: Encourage individuals who have experience in receiving foodborne illness complaints for many years to share “pearls of wisdom” such as the following:

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 their last meal (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.

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 2: Do you think the student’s complaint should be investigated further? (VOTE)

A)Definitely

B)Probably

C)Probably not

D)Definitely not

Ideally, all reports of possible outbreaks of foodborne illness 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 food preparation practices, and

3)Add to our knowledge of foodborne diseases.

Given resource constraints in many health departments, however, it might not be possible to investigate all individual cases of potential foodborne disease or investigate all cases to the same degree. Public health workers often must choose which instances receive highest priority for investigation. The highest priority usually should be given to outbreaks that:

  • Have a high public health impact because they:

Cause severe or life-threatening illness, such as infection with E. coli O157:H7, hemolytic uremic syndrome (HUS), or botulism;

Affect populations at high risk for complications of the illness (e.g., infants or elderly or immunocompromised persons); or

Affect a large number of persons.

  • Appear to be ongoing and associated with one of the following:

A food-service establishment in which ill food workers provide a continuing source of infection;

A commercially distributed food product that is still being consumed; or

  • A involve a suspected adulterated food.

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

  • Signs and symptoms (or confirmed diagnoses) among affected individuals suggesting they might not have the same illness,
  • Ill persons who are not able to provide adequate information for investigation including date and time of onset of illness, symptoms, or a complete food history,
  • Confirmed diagnosis and/or clinical symptoms that are not consistent with the foods eaten and the onset of illness, or
  • Repeated complaints by the same individual(s) with no significant findings upon investigation.

In this foodborne illness complaint, one might be a little skeptical. The student refused to give a food history beyond the foods eaten at the pizzeria and the question about attending classes and taking a midterm exam sounds a little suspicious (i.e., as if the roommates might just want an excuse to avoid an unpleasant situation). The fact that the student was not willing to give his or his roommate’s name, however, 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. Anonymous reports do make investigation and follow-up more challenging.

TDH staff were skeptical of the student’s report but felt that a minimal amount of exploration was necessary. They contacted the City Health Department to determine if staff were aware of a problem. City Health Department staff reviewed the foodborne illness complaint log to see if others had reported similar illnesses or exposures. Although a few reports of vomiting and diarrhea had been received, no other recent complaints mentioned the pizzeria or involved students from the university.

TDH staff then made a few telephone calls. 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 of a hospital close to the university (Hospital A) revealed that 23 university students had been seen for acute gastroenteritis in the last 24 hours. Based on the emergency room triage log, only three patients had been seen for similar symptoms from March 5-9, none of who were associated with the university. Stool specimens from 17 students had been submitted for routine bacterial pathogens to the Hospital Laboratory on March 10, but no results were available.

Around 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 at the clinic the previous day and more were waiting to be seen that morning. He believed only 1-2 students typically would have been seen for these symptoms in a week.

Question 3: Do you think these cases of gastrointestinal illness represent an outbreak at the university? Why or why not?

An outbreak is usually defined as two or more cases of a similar illness among individuals who have shared a common exposure. The critical components of this definition are:

  • Same diagnosis or symptoms and signs suggestive of same illness
  • Clear association between cases, with or without a recognized common source

The association between cases includes things such as attending the same event or going to the same school or eating the same food.

It seems likely that the cases of illness among students at the university represent an outbreak. What is not clear is whether the outbreak is limited to the university or if the wider community is also affected. Case finding methods to this point, utilizing a hospital near the university and the University Student Health Center, are more likely to pick up cases among students than in the community.

PART II - HYPOTHESIS GENERATION

TDH 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 of the university to report all patients with vomiting or diarrhea seen since March 5.

TDH investigators then visited the emergency room at Hospital A and reviewed medical records of the 26 patients seen at the facility for vomiting and/or diarrhea since March 5. All but three were students at the university. Based on these records, symptoms among the 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 [normal: 4.8-10.8 per cubic mm]).

Preliminary stool culture results from the 17 students from whom specimens had been collected did not identify Salmonella, Shigella, Campylobacter, Vibrio, Listeria, Yersinia, Escherichia coli O157:H7, Bacillus cereus, or Staphylococcus aureus. Examinations for ova and parasites were negative. Some specimens were positive for fecal leukocytes and fecal occult blood.

Question 4: How might you interpret the bacterial culture results?

Several explanations exist for the negative cultures:

  • Specimens may have been improperly collected or mishandled during storage, transport, or processing leading to the death of any biological pathogen present.
  • Specimens may have been collected too late in the course of the patients’ illnesses (i.e., the patients were no longer excreting the pathogen in adequate numbers for detection).
  • The illness may be due to some agent not tested for by the laboratory (e.g., virus or bacterial pathogen not routinely identified, parasite, preformed toxin, chemical agent).

Since the cultures were performed at the Hospital A laboratory, 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.

Question 5: Based on the findings so far, what type of agent do you think might be causing this outbreak? (VOTE)

A)Bacteria

B)Virus

C)Parasite

D)Preformed toxin or chemical

There are two broad classifications for gastrointestinal illnesses:

  • Infections are a consequence of the growth of a microorganism in the body. Illness results from two mechanisms: 1) viruses, bacteria, or parasites invade the intestinal mucosa and/or other tissues, multiply, and directly damage surrounding tissues and 2) bacteria and certain viruses invade and multiply in the intestinal tract and then release toxins that damage surrounding tissues or interfere with normal organ or tissue function. The necessary growth of the microorganism (for production and release of toxins) takes time; thus, the incubation periods for infections are relatively long, often measured in terms of days as compared to hours or minutes for preformed toxins. Symptoms of infection usually include diarrhea, nausea, vomiting, and abdominal cramps. Fever and an elevated white blood cell(WBC) count are often associated with infections.
  • Illness due to a preformed toxin is caused by ingestion of food already contaminated by toxins. Although sources of preformed toxins include certain bacteria, poisonous chemicals, and toxins found naturally in animals, plants, or fungi,these illnesses 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 preformed 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 is often measured in minutes or hours. Signs and symptoms depend on the specific toxin ingested. The most common (and sometimes only) symptom is vomiting. Other symptoms include nausea, diarrhea, and interference with sensory and motor functions (e.g., double vision, weakness, respiratory failure, numbness, tingling of the face). Fever and an elevated WBC count are rare with the ingestion of preformed toxins.

Based on the information collected so far, it would seem thatclinical findings (i.e., diarrhea, fever, an elevated white blood count, and fecal leukocytes) are most compatible with an infection. Given that cultures for the usual foodborne bacterial pathogens and examinations for ova and parasites were negative, a virusmight be the most likely causative agent.

By the next morning, 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, students living off-campus, 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. (N=72) (Date of onset was not known for three ill students.)