1. Outbreak Investigation
EPIET Introductory course 2006
Lazareto, Menorca, Spain

2. What is an outbreak ? Occurrence of more cases of disease
than expected
in a given area
over a particular period of time
among a specific group of people

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

4. Objectives for this session
Describe
the principles of outbreak investigation
the steps in outbreak investigation
Using practical examples
Outbreak of Hepatitis A in Ibiza, Spain September January 2001
Tomorrow
some operational and logistical aspects of outbreak investigation

5. Clinicians Epidemiology Co-ordination Food safety Laboratory
Dead
Sick
Investigation
Surveillance
Prediction
Exposed
Clinicians
Epidemiology
Co-ordination
Vector
Reservoir
Food safety
Laboratory
Clinical
Supply channels
Specimen
transfer
Trace
back
Investigation
Diagnostic
Media
Authorities
Decisions
Infrastructure
Regulations
Vaccinations etc

6. Specific demands when investigating outbreaks
Unexpected event
Act quickly
Rapid control
Interdisciplinary coordination
Work carried out in the field
Systematic approach

7. Outbreak of Hepatitis A in Ibiza (Spain) 2000/2001
Ibiza is a major tourist destination
(2 million visitors in 2000)
23-27 October 2000:
5 cases of Hepatitis A notified to local health authorities in Ibiza
3 cases of Hepatitis A among German tourists returning from Ibiza

8. 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

9. Detection Routine surveillance Clinical / Laboratory General public
Media
Detection

10. Notified cases of S. Bovismorbificans, Germany 2002-2005
2004
(n=153)
2003
(n=150)

11. 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)

12. Outbreak of Hepatitis A in Ibiza, Spain
Hepatitis A notifiable disease in Spain
notifications in Ibiza during previous years:
1997: 6 cases
1998: 0 cases
1999: 4 cases

13. 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

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

15. Outbreak confirmed, further investigations warranted
Form Outbreak Control Team
Epidemiologist
Microbiologist
Clinician
Environmentalist
Engineers
Veterinarians
Others
Team coordinates field investigation

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

17. 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

18. Case definition Simple, practical, objective Sensitive? Specific?
Multiple case definitions
confirmed
probable
possible

19. Case definition Outbreak of Hepatitis A in Ibiza 2000/2001
Any person
with IgM antibodies to Hepatitis A Virus
August January 2001
on the island of Ibiza for at least one day during a day period before onset of illness or seroconversion

20. Identify & count cases notifications hospitals, GPs laboratories
schools
workplace, etc
Identify & count cases

21. Case-finding Outbreak of Hepatitis A in Ibiza 2000/2001
Contacting clinicians and laboratories on the island
Note in German Epidemiological Bulletin
Enquiries through European network

22. Identify & count cases Obtain information
Identifying information Demographic information
Clinical details
Exposures and known risk factors

23. Obtaining information Outbreak of Hepatitis A in Ibiza 2000/2001
Trawling questionnaire
Place and time of stay on Ibiza
Food histories:
What eaten
Where bought?
Visit to restaurants

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

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

26. Analysis of descriptive data
Identify & count cases
Obtain information
Describe in
- time
- place
- person
Analysis of descriptive data

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

28. Epi 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

29. Common intermittent source
Examples of Epicurves
Common persistent source
Common point source
cases
cases
hours
days
Propagated source
cases
Common intermittent source
cases
weeks
days

30. Cases of Hepatitis A in Ibiza by week of onset, 2000/2001

31. Estimation of time or period of exposure
cases
max incubation
min
exposure

32. Outbreak of typhoid fever, Germany 2004

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

34. Cases of Hepatitis A in Ibiza by place of residence, 2000/2001
Portinatx
Ibiza-City
10 km

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

36. Outbreak of S. Agona, Germany 2003
2002
2003

37. Cases of Hepatitis A in Ibiza by age group, 2000/2001

38. 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?

39. exploratory interviews among cases of Hepatitis A, Ibiza 2000/01
3 potential risk factors:
visited a restaurant in the harbour of Ibiza town
bought food at a supermarket in the centre of the town
stayed at Hotel in Portinatx (German tourists)

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

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

42. Case-control study Outbreak of Hepatitis A in Ibiza 2000/2001
among residents of the island
one control per case
selected from the data-base of the health registration card
matching for age and neighbourhood
no history of hepatitis A disease or vaccination.

43. Cases of Hepatitis A and controls by exposure to restaurant and shop, Ibiza 2000/2001
Cases (n=38)
Controls (n=38)
matched OR
95% CI
Restaurant
22 (57.9%)
5 (13.2%)
9.0
Shop
13 (34.2%)
6 (15.8%)
4.5

44. Cases of Hepatitis A and controls by exposure to food items, Ibiza 2000/2001
Restaurant
Cases
n = 22
Controls
n = 5
Matched OR
95% CI
Salad 18
undef.
Shop
n = 13
n = 6
Sausages 11 3
5.5
Meat 10 4
1.67
Vegetables
Fish 9
1.13
Bread 8
0.8

45. 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

46. Viral genome sequencing Outbreak of Hepatitis A in Ibiza 2000/2001
Alignment of aminoterminal region of VP3
38 serum samples
Positive in 11 cases:
belonging to the three different groups
100% homology

47. Outbreak of S. Bovismorbificans, Germany 2004
Food trace-back NL
Outbreak of S. Bovismorbificans, Germany 2004

48. Implement control measures
1) Control the source of pathogen
2) Interrupt transmission
3) Modify host response
At first, general measures
According to findings, more specific measures
May (must) occur at any time during the outbreak!!

49. Recommendations Outbreak of Hepatitis A in Ibiza 2000/2001
Emphasise hygiene amongst food handlers
Strengthen surveillance for foodborne diseases
Enhance international co-operation

50. 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

51. 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

52. The reality…. time Site visit Case definition Recommendations Report
Publication
Confirmation
Organize Data
Descripitve
Epidemiology
Confirm Diagnosis
Info:
Outbreak
suspected
Line list
Analytic
Epidemiology
Form Outbreak Control Team
Control measures