Outbreak Investigation Assignment -
Scenario: You are working as an epidemiologist in a public health unit in Tamworth, Australia. You receive a call from a local P. She reports five children in the last 2 days presented with 2-4 episodes of watery diarrhea and some with vomiting. Some reported fever. The children were in year 7 of a local public high school in a suburb "A". You phone the local hospital emergency department who confirmed the collection of faecal specimens from some children who presented with gastroenteritis, but results are not yet available. Based on this initial report please answer the following questions.
1. What will you do to confirm the existence of an outbreak?
2. You determine that an outbreak may be occurring. How will you confirm the diagnosis?
Scenario (continued)
A few days later, you receive reports of nine adult cases of diarrhea with or without vomiting that presented over three days to a public hospital in a nearby suburb - "B". They were adults aged 20-59 years. You obtain additional information from the GP and hospital records on the cases from both suburbs and prepared the following line listings.
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Table 1: Line list of cases in Suburb "A"
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|
ID
|
Name
|
Age (years)
|
Sex
|
Date of symptom onset
|
Symptoms
|
Lab Result
|
|
Diarrhea
|
Vomiting
|
Fever
|
|
1
|
A1
|
12
|
M
|
11-12-2018
|
+
|
-
|
+
|
Pending
|
|
2
|
A2
|
11
|
F
|
11-12-2018
|
+
|
+
|
-
|
Pending
|
|
3
|
A3
|
12
|
M
|
12-12-2018
|
+
|
-
|
+
|
Pending
|
|
4
|
A4
|
13
|
F
|
12-12-2018
|
+
|
-
|
+
|
Pending
|
|
5
|
A5
|
12
|
F
|
12-12-2018
|
+
|
+
|
+
|
Pending
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M = male, F = female, "+" means symptom is present, "-" means symptom is absent.
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Table 2: Line list of cases in Suburb "B"
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|
ID
|
Name
|
Age (years)
|
Sex
|
Date of symptom onset
|
Symptoms
|
Lab Result
|
|
Diarrhea
|
Vomiting
|
Fever
|
|
1
|
B1
|
21
|
F
|
15-12-2018
|
+
|
+
|
-
|
Pending
|
|
2
|
B2
|
44
|
F
|
15-12-2018
|
+
|
-
|
+
|
Pending
|
|
3
|
B3
|
20
|
M
|
15-12-2018
|
+
|
-
|
+
|
Pending
|
|
4
|
B4
|
25
|
F
|
15-12-2018
|
+
|
+
|
+
|
Pending
|
|
5
|
B5
|
34
|
F
|
15-12-2018
|
+
|
+
|
+
|
Pending
|
|
6
|
B6
|
21
|
M
|
16-12-2018
|
+
|
+
|
+
|
Pending
|
|
7
|
B7
|
47
|
F
|
17-12-2018
|
+
|
-
|
-
|
Pending
|
|
8
|
B8
|
32
|
F
|
17-12-2018
|
+
|
-
|
+
|
Pending
|
|
9
|
B9
|
28
|
F
|
17-12-2018
|
+
|
+
|
-
|
Pending
|
M = male, F = female, "+" means symptom is present, "-" means symptom is absent.
3. Draw an epidemic curve using Microsoft Excel Include data from both suburbs. What might explain the pattern?
(Hints: do not treat cases from each suburb any differently. Include dates with zero counts. Include an accurate title for your epidemic curve. Label both your axes)
Scenario (continued)
You receive laboratory reports of the faecal samples taken from the affected cases. Out of 14 specimens from both suburbs, seven showed the presence of Salmonella Enteritidis, one showed the presence of Shigella and six were negative for any pathogen tested.
4. What would be your case definition based on the available information? Please explain your answer.
Scenario (continued)
You decide to visit the affected suburbs and interview the cases (or their carers) to further investigate the outbreak. All cases in Suburb "A" reported eating fresh salad with mayonnaise during a school picnic that was bought from the local supermarket a few days before the diarrhea started, and a few cases reported eating fried ice cream from a local restaurant during the last week. The restaurant reported they had a refrigerator break-down two weeks earlier and it was repaired the same day. The supermarket prepared their own salads for sale.
On the other hand, most cases in suburb "B" reported eating frozen berries bought from the same supermarket during the last four weeks and a few reported eating salad sandwiches from a local sandwich shop, one or two days before diarrhea started.
You observed good hygiene, cleanliness and food preparation practices in the supermarket, sandwich shop and restaurant. A staff member in the sandwich shop was a new arrival in Australia and started work almost immediately in the sandwich shop. The supermarket and sandwich shop both recently started buying an egg-based mayonnaise from a new local supplier.
5. Based on the findings so far, what hypotheses can be generated from the interview data? Please explain your answer.
6. What type of analytical study would you conduct to test these hypotheses? Why? What are some considerations when developing the study protocol?
Scenario (continued)
The study finds the strongest association with sandwiches and salads containing mung bean sprouts. These were an ingredient in ready-made salads sold at the supermarket and the sandwich shop. They were also used in salad sandwiches prepared at the sandwich shop.
7. What other things would you consider before deciding on the conclusions from your analytical study?
8. What would you do to determine whether your analytical study findings are plausible and consistent with the observed outbreak?
9. What are some important considerations you would cover when communicating your findings? Who would be your stakeholders?
10. What specific recommendations would you make to prevent similar outbreaks in the future? Describe roles and responsibilities of the various stakeholders.