Disease
Detectives
B Division Regional
2011
Do not open until instructed to do so.
All answers should be written in the space provided on your answer sheet
You may take apart this test and use any blank spaces as scratch unless instructed otherwise by the
event proctor
Part I: Questions 1-14 relate to the following story, taken from Korff, Taback and Beard, “A
Coordinated Investigation of a Food Poisoning Outbreak,” Public Health Reports 69:9 909-913
Sept. 1952.
On July 19th, 1951, public health officials in Baltimore received news of a suspected outbreak of
food poisoning at a local resort. The previous day, a local an insurance company had held a
company picnic for 332 employees and their guests. After an afternoon of swimming, horseshoes
and softball, a buffet dinner was served. The food items offered included sliced cooked ham, fried
crab cakes, potato salad, sliced tomatoes, heated baked beans, sliced bread, ice cream, cake and
hot coffee, served on paper plates. After collecting the above information from the company,
public health officials contacted the food service manager at the resort on the 20th, who informed
them that all of the leftover food had been thrown away and the garbage removed. One of the
resort’s two refrigerators was in use but not functioning, with a measured interior temperature of
70 °F. In addition, the work-table surface was cracked, the meat grinder had putrified meat
adhering to it, there was no three compartment sink, and there were no convenient hand washing
facilities. The water was from the resort’s own well, which tested negative for coliform bacteria.
Dinner was served at 6:00 P.M. The crab cakes were formed by the cook with his hands out of
canned crab meat, bread crumbs, Worcestershire and Tabasco sauce, parsley and pimentos, and
were fried in deep fat at approximately 350 °F shortly before they were served. The potato salad
consisted of cut potatoes, mayonnaise, onions, peppers, pimento, celery seed, pickled relish,
vinegar, salt and pepper. These ingredients had been purchased from a large restaurant supply
company and were mixed by the cook with his hands approximately four hours before the salad
was served. Information about the picnickers’ symptoms and food consumption was collected via
a questionnaire which was distributed to all of the attendees who could be reached. 304
individuals responded, 146 of whom reported becoming ill, primarily with nausea and vomiting.
This data is summarized in Figure 1 and Table 1, respectively.
Figure 1:
Table 1:
Food item
Total eating
Number ill
Ham
230
108
Crab cake
235
124
Potato salad
246
142
Tomatoes
253
127
Ice cream
201
98
Beans
258
129
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1. Investigators almost immediately concluded that the most likely agent was Staphylococcus
aureus. What evidence led them to do so?
2. Why was it a problem for investigators that the leftover food had been thrown away?
3. Why were investigators concerned with the temperature in the refrigerator?
4. Why were investigators concerned with the temperature in the cooking fat?
5. Why are food service facilities required to have a three compartment sink? What are the
three compartments for?
6. Why is the cracked work surface potentially significant?
7. Why did investigators test the well for coliform bacteria?
a) Only coliform bacteria such as E. coli could be found in water and cause the symptoms
shown
b) The test for coliform bacteria is a relatively quick and cheap way of determining
whether a water source has been contaminated with fecal matter
c) There were no tests for other forms of bacteria in 1951
d) Investigators suspected S. aureus, which is a coliform bacteria
8. Use the data provided above to complete the table on your answer sheet (including labels) and
calculate the risk of illness associated with each of the listed food items. (5 pts)
9. Calculate the relative risk for each food item, using total respondents as your baseline. (6 pts)
10. Which food item was the most likely source of illness and why? (2 pts)
11. Like peanuts, tree nuts and shellfish, celery seed is capable of provoking an anaphylactic
reaction in susceptible individuals. Explain why an allergy to celery seed was not seriously
considered by investigators in this outbreak.
12. Is commercially prepared mayonnaise commonly associated with food poisoning? Why or why
not?
13. From the data provided, what seems to have been the median incubation period?
14. How did the bacteria most likely get in to the infected food?
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Part II: Questions 15-27 relate to the following account is paraphrased from MacDonald et al.,
“Type A Botulism,” Journal of the American Medical Association 253:9 1275, March 1985.
Between Saturday, Oct. 15 and Thursday, Oct. 20, 1983, twenty-eight persons were hospitalized in
Illinois with neurological signs and symptoms such as double vision (diplopia), dry mouth, difficulty
swallowing (dysphagia), extremity weakness and respiratory failure. All of these symptoms are
characteristic of botulism. The first three patients all reported having eaten the same food at the
same restaurant the previous day (Friday the 14th); this food consisted of a patty-melt sandwich,
French fries, lettuce, tomatoes and a pickle spear. All of the restaurant’s pickles were promptly
confiscated by public health officials, but since restaurant patrons continued to report to hospitals
with neurologic symptoms, the restaurant was closed on the following day (Sunday the 16th).
Samples of various foodstuffs were collected and sent to Atlanta for analysis, and questionnaires
were administered to all of the case patients and also to four other groups: 24 employees of the
restaurant who had worked during the three day period (14th-16th); 43 employees of other
businesses in the retail mall where the restaurant was located; 14 customers of the restaurant in
the period in questions, identified by credit card receipts; and 38 people who had eaten at the
restaurant in the company of one or more of the case-patients. Table 2 summarizes the results.
The results from laboratory analysis of the food samples implicated the onions, which was
surprising to the investigators. They questioned the restaurant owner about the method of
preparation, who revealed that the onions were kept on a grill under a thick layer of melted
margarine, and served with tongs that were also used for other food items. The owner
maintained that the onions were discarded each day, but in researchers’ replication of these
conditions, 48 hours were required for sufficient bacterial growth.
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15. Develop a case definition for this outbreak (3 pts).
16. Why did public health officials at first suspect the pickles (2 pts)?
17. To what organization in Atlanta were the samples most likely sent?
18. a. Why were questionnaires sent to people without symptoms?
b. What are these people called?
19. What type of study was conducted here?
20. Place the data provided above into the data table. Calculate the odds of having eaten the
patty melt for each of the groups studied. (4 pts)
21. Calculate the odds ratio for patients compared to all others. (3 pts)
Figure 2:
22. What was the most common incubation period for these patients?
23. What term is used to describe this type of graph?
24. a. Compare the incubation period for patients requiring ventilator support to that of other
patients.
b. What might explain this difference?
25. What type of outbreak is indicated by this graph?
26. Why is it important that the onions were kept under a layer of margarine?
27. If the onions were the source of contamination, how can the illness of the four patients who
did not eat the patty melt be explained?
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Part III:
28. Some tropical plankton produce toxic chemicals such as ciguatoxin, which can be picked up by the fish
which eat the plankton. Why are levels of ciguatoxin are likely to be highest in the largest fish?
29. Which of the following best represents the “danger zone” of temperatures for bacterial growth?
a) 0-100 °F
b)20-120 °F
c) 40-140 °F
d) 60-200 °F
e) <20 or >120 °F
30. Boiling in water for ten minutes
a) Kills all bacteria and viruses and destroys all bacterial toxins
b) Kills all bacteria but does not destroy all bacterial toxins
c) Kills all bacteria and destroys all bacterial toxins, but does not destroy all viruses
d) Kills most bacteria and viruses and destroys some toxins
e) Has no effect on most bacteria, viruses and toxins
31. In addition to microorgansims, food poisoning can be caused by toxins commonly found in
a) Plant leaves
b) mushrooms
c) fish
d) fruit
e) all of the above
32. In some decaying fish, histidine is converted to histamine by the action of bacteria. This histamine can
cause a highly unpleasant but generally non-life threatening reaction called
a) Scombroid poisoning
b) Ptomaine poisoning c) Mycotoxicosis
d) Toxic shock
33. Multicellular parasites are most likely to cause disease in humans if ingested in which life stage?
a) spore
b) egg
c) larva
d) nymph
e) adult
For questions 35 – 46, choose the letter of the answer at right that best matches each question at left.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
Cholera in Haiti in 2010-11
The common cold in the U.S. in 2010-11
Mosquitoes, for malaria
Kitchen implement, work surface etc. which
transmits disease
Time between infection and first
appearance of symptoms
Ability of a pathogen to cause disease
Proportion of exposed population which is
infected
A number of cases
A higher than expected number of cases in
a region and time period
Why most vaccinated people in the US do
not get polio
Why most unvaccinated people in the US do
not get polio
Structural component of some bacteria
which may cause illness
Substance secreted by some bacteria that
may cause illness
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
M.
N.
O.
P.
Q.
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Active Immunity
Agent
Attack Rate
Cluster
Endemic
Endotoxin
Epidemic
Exotoxin
Fomite
Herd Immunity
Incubation period
Outbreak
Pandemic
Passive Immunity
Reservoir
Vector
Virulence
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