Investigating an Outbreak of Acute Gastrointestinal Illness

Part I: Outbreak Detection

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 mid-term exam that was scheduled that afternoon.

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

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

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

Question 4: Do you think these cases of gastroenteritis represent an outbreak at the university? Why or why not?

Part II Initial Microbiologic Investigation

On the afternoon of March 11, TDH staff visited the emergency room at Hospital A and reviewed medical records of patients seen at the facility for vomiting and/or diarrhea since March 5. Based on these records, symptoms among the 23 students included vomiting (91%), diarrhea (85%), abdominal cramping (68%), headache (66%), muscle aches (49%), and bloody diarrhea (5%). Oral temperatures ranged from 98.8° F (37.1° C) to 102.4° F (39.1° C) (median: 100° F [37.8° C]). Complete blood counts, performed on 10 students, showed an increase in white blood cells (median count: 13.7 per cubic mm with 82% polymorphonuclear cells, 6% lymphocytes, and 7% bands). Stool specimens had been submitted for routine bacterial pathogens, but no results were available.

Question 5: List the broad categories of diseases that must be considered in the differential diagnosis of an outbreak of acute gastrointestinal illness.

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

Question 7: What information should be provided with each stool specimen submitted to the laboratory? How will the information be used?

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

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

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.  TDH staff met with the Student Health Center physician and nurse, and several university administrators including the Provost. City health department staff participated in the meeting.

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

Question 11: Using information available to you at this point, state your leading hypothesis(es) on the pathogen, mode of transmission, source of the outbreak, and period of interest.

Question 12: What actions would you take?

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: What key areas should be explored during interviews with the cafeteria foodhandlers?

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