1. Biagio Pedalino & Domenico Martinelli
Outbreak investigations
Biagio Pedalino & Domenico Martinelli
24th October 2012

2. Objectives for this session
Describe
the principles of outbreak investigation
the steps in outbreak investigation
Using practical example
Foodborne outbreak during a birthday party in a pub

3. What do you normally do on Sunday afternooon?

4. Something funny.
We had lunch at sibilla’s. We were 13 and now 7 are vomiting…
Roberto, 41
Pub owner
Excellent. Do you need me to be there for the “plasil”? Have you eaten something with cream?

5. What is it? Friendly call Need of medical assistance? Coincidence?
What else?...
Outbreak?

7. What is an outbreak ?
“The occurrence in a community or region of cases of an illness (or an outbreak) with a frequency clearly in excess of normal expectancy”
[Heymann DL, CDC Manual – 19th Ed]

8. Outbreak investigation: tasks
Confirm outbreak and diagnosis
Form Outbreak Control Team
Define a case (case definition)
Identify cases and obtain information
Describe data by time, place, person
Develop hypothesis
Test hypothesis: analytical studies
Additional studies
Communicate results:
outbreak report, publication
Implement control measures
Communication
Control measures

9. Confirm outbreak Is this an outbreak? More cases than expected?
Surveillance data
Surveys: hospitals, labs, physicians
Caution!
Seasonal variations
Notification artefacts
Diagnostic bias (new technique)
Diagnostic errors (pseudo-outbreaks)

10. Confirm diagnosis Laboratory confirmation Meet attending physicians
serology
isolates, typing of isolates
toxic agents
Meet attending physicians
Examine some cases
Contact (visit) the laboratories
Not always necessary to confirm all the cases
but confirm a proportion
throughout the outbreak

11. Outbreak confirmed  Immediate control measures? - prophylaxis
- exclusion / isolation
- public warning
- hygienic measures
- others

12. Alert !!! Informal alert from the pub
7 participants were sick with vomit
Formal intervention: a simple phone call !

13. Phone call 4:45 pm Talk to the pub owner
How many people (list with contact details)
Food items
Symptoms/treatment
“Impose” preventive closure of the pub

14. Immediate control measures? Further investigation?
Outbreak confirmed 
Immediate control
measures?
Further
investigation?
- prophylaxis
- exclusion / isolation
- public warning
- hygienic measures
- others
- etiological agent
- mode of transmission
- vehicle of transmission
- source of contamination
- population at risk
- exposure causing illness

15. Steps of an outbreak investigation
Control measures
Confirm outbreak and diagnosis
Form Outbreak Control Team
Define a case
Identify cases and obtain information
Describe data by time, place, person
Develop hypothesis
Test hypothesis: analytical studies
Additional studies
Communicate results:
outbreak report, publication
Implement control measures

16. My outbreak control team
Ale, Preventive medicine school student - II yr
Fra, PHD student - I yr

17. Case definition
A person presenting with vomit or nausea or diarrhoea, within 24 hours after participating at the meal in the pub (Sunday January 22nd; 2pm)

18. Case definition
Standard set of criteria for deciding if a person should be classified as suffering from the disease under investigation
Criteria
clinical and/or biological criteria
time
place
person

19. Case definition Simple, practical, objective Sensitive? Specific?
Multiple case definitions
confirmed
probable
possible
CD can be adjusted, if new information becomes available

20. Steps of an outbreak investigation
Control measures
Confirm outbreak and diagnosis
Form Outbreak Control Team
Define a case
Identify cases and obtain information
Describe data by time, place, person
Develop hypothesis
Test hypothesis: analytical studies
Additional studies
Communicate results:
outbreak report, publication
Implement control measures

21. Descriptive epidemiology
When did they become ill? (time)
- Where do they live? (place)
- Who are the cases? (person)

22. Identify & count cases Obtain information
notifications
hospitals, GPs
laboratories
schools
workplace, etc
Identify & count cases
Obtain information
Identifying information Demographic information
Clinical details
Exposures and known risk factors

23. Monday 8 am Contact the participants: In the pub
Symptoms
Food consumption
Stool specimen collection (n=5)
In the pub
Food samples collection
Info on food preparation

24. Information collected: symptoms
14:00: lunch (13 participants: birthday party)
12 were sick
Vomit (n= 10)
Nausea (n=9)
Diarrohea (n=5)
Abdominal pain (n=6)
Fever (<38°C; n=2)

25. Information collected: food consumption (n=13)
Basmati rice: 92% (12)
Ragu’ : 77% (10)
Red rice: 69% (9)
Apple cake: 61% (8)

26. Possible cause of the outbreak?
Virus ?
Bacteria ?
Toxins ?
Parasite ?

28. Organize information: Line list
Names
Date of birth
Addresse
Onset of symptoms
Treating physician
Hospital stay
Laboratory results

29. Line List Case No. Name Date of birth Addresse Date of onset Lab
results 1 2 3 4 5 6 XY AB CD …

31. Identify & count cases Obtain information Descriptive study
Describe in
- time
- place
- person
Descriptive study

32. Time: Epidemic Curve Histogram
Distribution of cases by time of onset of symptoms, diagnosis or identification
time interval depends on incubation period
Cases
Days

33. Epidemic curve Describe Helps to develop hypotheses atypical cases
start, end, duration
peak
importance
atypical cases
Helps to develop hypotheses
incubation period
etiological agent
type of source
type of transmission
time of exposure
Days

34. Examples of Epidemic curves
Common persistent source
Common point source
cases
cases
hours
days
Propagated source
cases
Common intermittent source
cases
weeks
days

35. Hepatitis A by date of onset Ogemaw county, Michigan, April - May 1968
Number of cases 15
one case
50 days
30 days 10 5
15 days
In an ideal situation if we are looking at a point source outbreak, we know that point source outbreaks have a normal distribution, so we have all people who have been exposed distributed according.
Now, if we look at the graph, what we have here is the distribution of Hep A cases by date of onset. So according to a normal distribution of cases, the first case here would represent those cases in the outbreak who had the shortest incubation period or minimum incubation period. Those in the end would represent those who had the longest incubation period, and those in the middle would be those who had a median incubation period.
So, by using our knowledge of infectious diseases, and double checking text books and references, we simply take the first cases and go back the minimum incubation period, the last and we go back the max incubation period and the one in the middle and we go back the median incubation period to identify the possible window of exposure that may explain the cases in our outbreak
The identification of a possible window of exposure can help us a lot if we want to further investigate the outbreak by administering a questionnaire about a possible food consumption or exposure to other possible risk factors.
Therefore, when interviewing our cases, instead of focusing on a large window of exposure, and when it comes to consumption of food items, the shorter is the window, the better, we can focus on a much smaller window of exposure, and maybe also use a particular date around an event or something that people would better remember.
But again, that’s in the ideal world… 2 8 14 20 26 2 8 14 20 26 1 7
Exposure
Days

36. ~ median incubation period (= duration of the epidemic)
Hypothesis on the moment of infection unknown pathogen and point source 2
~ median incubation period
(= duration of the epidemic) 3
Possible moment of infection 1
median
50% % 15 5
Time 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

37. Epi curve
Incubation period:
Median = 2 hrs
Range = 1-5 hrs

38. Place Place of residence Place of possible exposure work meals
travel routes,
day-care
leisure activities
Maps
identify an area at risk

41. Person Distribution of cases age sex occupation, etc
Distribution of these variables in population
Attack rates

42. Sick Sick Not-sick Sick Sick
Roberto
41 yrs old
Marygiò
42 yrs old
Massimo
40 yrs old
Sick
The grandmother, 70 yrs old
Sick
Not-sick
Barbara
34 yrs old
Yasemin
35 yrs old
Sick
Sick

43. Steps of an outbreak investigation
Control measures
Confirm outbreak and diagnosis
Form Outbreak Control Team
Define a case
Identify cases and obtain information
Describe data by time, place, person
Develop hypothesis
Test hypothesis: analytical studies
Additional studies
Communicate results:
outbreak report, publication
Implement control measures

44. Develop hypotheses - What is the disease?
- Who is at risk of becoming ill?
- What is the disease?
- What is the source and the vehicle?
- What is the mode of transmission?

45. Hyp in the pub: summary Close community 12 out of 13 were sick
Mainly vomit
Basmati rice mostly consumed food
Basmati rice left out of the fridge for > 24hrs

46. Test specific hypotheses
Compare hypotheses with facts
Test specific hypotheses
Analytical studies
- cohort studies
- case-control studies

47. Testing hypothesis Cohort attack rate exposed group
attack rate unexposed group
Case control
proportion of cases exposed
proportion of controls exposed

48. Cohort study
Among participants
Telephone interviews

49. Description of the cohort
13 persons
54% F
Median age: 42 (15 – 70)
Overall Attack Rate (AR): 92%
Food specific AR:
Basmati rice: 100%
Apple cake: 100%
Ragu’: 91%
Red rice: 90%

50. Steps of an outbreak investigation
Confirm outbreak and diagnosis
Form Outbreak Control Team
Define a case
Identify cases and obtain information
Describe data by time, place, person
Develop hypothesis
Test hypothesis: analytical studies
Additional studies
Communicate results:
outbreak report, publication
Implement control measures
Control measures

51. Additional investigations
Verify hypothesis
Additional investigations
Microbiological investigation of food samples
Environmental investigation
Veterinarian investigation
Molecular Typing
Trace back investigations (origin of foods)
Meteorological data
Entomological investigations

52. Tuesday 10 am: laboratory results
Bacillus cereus

53. Tuesday 10 am: laboratory results
2/5 faecal specimens
Bacillus cereus

54. Steps of an outbreak investigation
Control measures
Confirm outbreak and diagnosis
Form Outbreak Control Team
Define a case
Identify cases and obtain information
Describe data by time, place, person
Develop hypothesis
Test hypothesis: analytical studies
Additional studies
Communicate results:
outbreak report, publication
Implement control measures

55. Outbreak report Regular updates during the investigation
Detailed report at the end
communicate public health messages
influence public health policy
evaluate performance
training tool
legal proceedings

56. Actions & Recommendations
Pub closed for one day
Appropriate food preparation (cold chain, storage, etc)
Timely alert for prompt intervention
… To follow grandmother’s wisedom… « no thanks, no rice for me… »

57. The reality…. time Communication Site visit Case definition
Recommendations
Report
Publication
Confirmation
Organize Data
Descripitve
Epidemiology
Confirm Diagnosis
Outbreak
suspected
Line list
Analytical
Epidemiology
Form Outbreak Control Team
Control measures
Communication

58. Why investigate outbreaks?
Stop the outbreak
Understand what happened and why
Prevent future outbreaks
Improve our knowledge
Improve surveillance and outbreak detection
Training

59. Acknowledgements Pub owner
Participants of the party (special thanks to the grandmother)

60. Questions ???