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Problem: Gastroenteritis

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Outbreak of gastroenteritis following a retirement party at the State Capitol

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Approximately 300 persons attended a retirement party at the Nebraska State Capitol held on May 27, 1999. Most of the attendees worked in the Capitol. A private caterer (Caterer A) prepared and served food for the reception. Based on initial telephone interviews of persons reporting illness, the predominant symptoms were nausea and diarrhea, and the incubation period was approximately 24-30 hours.

The following foods were served at the retirement reception: Swedish meatballs, taco dip, crab dip, a vegetable tray and herbed ranch dip, cake, nuts and mints. The vegetable tray consisted of cucumbers, broccoli, cauliflower, carrots, celery, green peppers, and radishes. All foods were prepared onsite on the day of the reception with the exception of the nuts, which were purchased by a coworker, and the mints, which were made by a coworker.

The Swedish meatballs consisted of ground beef, ground pork, sour cream and flour. The meatballs were cooked twice. The taco dip contained layers of cream cheese mixed with salsa, ground beef, tomatoes, lettuce, onion, cheese and salsa. The taco dip was prepared manually by Caterer A in the kitchen at the State Capitol, and was not cooked after assembly. The crab dip contained canned real crab, cream cheese and ketchup.

The investigators received completed surveys from 227 attendees. Of those 227 attendees, 128 (56%) persons reported a gastrointestinal illness within 72 hours of the reception. The average interval between time of food consumption and onset of illness was 32.3 hours (range 6 to 67 hours). Table 1 shows the symptoms reported by ill attendees. The duration of symptoms generally lasted 24 to 36 hours. One person reported being symptomatic for five days. Eight persons sought medical treatment, mostly for re-hydration therapy.

Persons working in the security office at the State Capitol ate samples of the items served at the reception except the taco dip. None of the people from this office reported illness. Table 2 shows the association of illness and eating the taco dip.

Table 1: Distribution of Symptoms Reported in Persons Meeting the Case-definition.

Table 2: Association of Illness and Exposure to Taco Dip

Questions

1. Write a case definition for this outbreak. (5 points)
   
   
   
2. Calculate the attack rate for persons eating the taco dip. Round to the nearest percentage. Please show your work. (3 points)
   
   
   
3. Calculate the relative risk for the exposure to taco dip and illness. Round answer to the nearest tenth. Please show your work. (5 points)
   
   
   

Which of the following agents most likely caused this outbreak. Briefly describe your answer. (5 points)

*Most common, as established by CDC:

1) Improper holding temperatures;
2) Inadequate cooking;
3) Contaminated equipment;
4) Food from unsafe source;
5) Poor personal hygiene
6) Other

1. An epidemic curve (2 points)

   A. graphically displays the scope of an outbreak
   B. shows the number of people affected by an outbreak
   C. shows the course of the outbreak over time
   D. all the above
   E. A and B

   Please match the following words with the most correct definition.

   Mean
   Endemic
   Epidemic
   Median
   Incidence
   Mode
   Prevalence
   Pandemic
   
   
   

2. A measure of the frequency of a new injury or case of illness in a population. (2 points)
   
   
   
3. The occurrence of more than the expected number of cases of a particular disease, chronic condition, or injury occurring over a very wide area (several countries or continents). (2 points)
   
   
   
4. The middle value in a set of numbers (or the average of two middle numbers) above and below which lie an equal number of values. (2 points)
   
   
   
5. The occurrence of the expected number of cases of a particular type of disease, chronic condition, or injury in a given area, or among a specific group of people, over a particular period of time. (2 points)
   
   
   

Answer Key

Tiebreaker #1

Please match the disease with the outbreak.

A. Cholera
B. HIV/AIDS
C. Salmonella
D. Influenza
E. Plague
F. Smallpox
G. Malaria

1. __ The Black Death, Europe, Middle Ages

2. __ Worldwide respiratory illness epidemic, 1918-19

3. __ Waterborne outbreak, London 1854

4. __ Rare Cancer-cluster identified, LA 1980-81

5. __ Schwan's ice cream, US, 1994

Answer Key

Tiebreaker #2

The rates described in the articles are what type of rates?

A. Incidence rates
B. Point prevalence rates
C. Morbidity rates
D. Mortality rates
E. Attack rates

Answer Key

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