Outbreak Investigation

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, SpainSeptember
  2000 - January 2001
• Tomorrow
• some operational and logistical aspects
  of outbreak investigation

5
Dead
Sick
Surveillance
Investigation
Exposed
Prediction
Clinicians
Epidemiology
Vector Reservoir
Food safety
Laboratory
Clinical
Supply channels
Specimen transfer
Trace back
Investigation
Diagnostic
Authorities
Media
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

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

• 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
Routine surveillance Clinical /
Laboratory General public Media
Detection
10
Notified cases of S. Bovismorbificans, Germany
2002-2005
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
• 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
Outbreak confirmed ?
- 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
Epidemiologist Microbiologist Clinician Environmen
talist Engineers Veterinarians Others
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 2000 - January 2001
• on the island of Ibiza for at least one day
  during a 15-50 day period before onset of illness
  or seroconversion

20
Identify count cases
21
Case-findingOutbreak 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
23
Obtaining informationOutbreak 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
26
Identify count cases
Obtain information
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
Cases

• Describe
• 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
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
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
2003
37
Cases of Hepatitis A in Ibiza by age group,
2000/2001
38
Develop hypotheses

• - 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
Compare hypotheses with facts
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
44
Cases of Hepatitis A and controls by exposure to
food items, Ibiza 2000/2001
45
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
Food trace-back
NL
Outbreak of S. Bovismorbificans, Germany 2004
48
Implement control measures
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
Analytic Epidemiology
Line list
Form Outbreak Control Team
Control measures