plying Epidemiology

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Epidemiological Case #1: Gastroenteritis at a University in Texas

PART I

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 mid-term exam that was scheduled

that afternoon.

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

Question 2: Do you think this complaint should be investigated further?

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

Why or why not?

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

laboratory? How will the information be used?

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

results raise?

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.

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

was not known for three ill students.)

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

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

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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 7: 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.

Question 8: What actions would you take? Who would you question? Where might you look for

the origin of the pathogen?

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

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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 5th-10th and where the foods were eaten. All information was collected over the telephone.

Question 9: What are the advantages and disadvantages of undertaking a case-control study

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

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

most notable results in Table 1.

Table 1. Risk factors for illness, matched case-control study, main cafeteria, University X, Texas, March 1998.

Exposure

Ill Exposed/

Total ill* (%)

Well Exposed/

Total well* (%)

Matched

Odds Ratio**

95%

Confidence

Interval

p-value

Ate at deli bar –

lunch on March 9

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

Ate at deli bar –

dinner on March 9

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

Ate at deli bar –

lunch on March 10

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

Ate at deli bar - dinner

on March 10

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

Ate at deli bar –

lunch or dinner on

March 9 or lunch on

March 10

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

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

meal.

**The data provided for cases and controls cannot be used to calculate the matched odds ratio which is based on an

analysis of discordant pairs.

Question 10: How do you interpret these data?

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Question 11: During which time/s and dates were students more likely to become ill?

Question 12: Who might you consult in developing actions/policies for the campus food service to

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

PART II

Based on this week’s readings and your knowledge of epidemiological concepts address the following

questions:

Which offices need to respond? How would you coordinate a response?

Did the case require an immediate public health response?

Determine what type of emergency is described in the case. Is this an epidemic, endemic,

pandemic or an isolated incidence?

List categories and examples of questions that should be asked of key informants who report a

suspected outbreak of foodborne disease

List four criteria for prioritizing the investigation of suspected foodborne disease outbreaks (if

applicable)