Principles of Outbreak
Management
WHO/CSR
Definition of outbreak
• Occurrence of more cases of disease than
expected in a given area among a specific
group of people over a particular period of
time
or
• Two or more linked cases of the same
illness
WHO/CSR
Objectives of outbreak
investigations
• To control continuing outbreaks
• To prevent future outbreaks
• To provide statutorily mandated services
• To strengthen surveillance at local level
• To advance knowledge about a disease
• To provide training opportunities
WHO/CSR
Specific demands when
investigating outbreaks
• Unexpected event
• Need to act quickly
• Need for rapid control
• Work carried out in the field
Systematic approach
WHO/CSR
Steps of an outbreak
investigation
•
•
•
•
•
•
•
•
Confirm outbreak and diagnosis
Case definition and identification
Descriptive data collection and analysis
Develop hypothesis
Analytical studies to test hypotheses
Special studies
Implementation of control measures
Communication, including outbreak report
WHO/CSR
Detection
Routine surveillance
Clinical / Laboratory
General public
Media
Is this an outbreak?
Diagnosis verified ?
clinical + laboratory
Link between cases?
Expected numbers?
WHO/CSR
Sequence of Events in outbreak detection and
confirmation (I)
Primary 1st case
Case
at HC
Report Samples Lab
to DMO taken result
Response
begins
90
80
70
60
50
Opportunity
for control
40
30
20
10
WHO/CSR
DAY
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
0
1
CASES
Sequence of events in outbreak detection and
confirmation (II)
Response
PRIM HC REP SAMP RES begins
40
WHO/CSR
37
34
31
28
DAY
25
22
19
16
13
10
7
Potential
Cases Prevented
4
1
CASES
90
80
70
60
50
40
30
20
10
0
Outbreak confirmed
Immediate control
measures?
Further
investigation?
WHO/CSR
Outbreak confirmed
Immediate control
measures?
Prophylaxis
Exclusion / isolation
Public warning
Hygienic measures
Further
investigation?
Unknown aetiology
(pathogen/source/transmission)
Cases serious
Cases still occurring
Public pressure
Training opportunity
Scientific interest
Assistance ?
WHO/CSR
Epidemiologist
Microbiologist
Environmental specialist
Ministry / Government
Press officer
Others
Outbreak
Investigation
Team?
FIELD
WHO/CSR
Investigation
Vector
Reservoir
Surveillance
Dead
Sick
Prediction
Exposed
Clinicians
Epidemiology
Coordination
Education
Laboratory
Clinical
Health
personnel
Special
groups
Specimen
transfer
General
population
Diagnostic
Media
Authorities
Decisions
Infrastructure
Regulations
Vaccinations etc
WHO/CSR
Epidemiologist
Microbiologist
Environmental specialist
Ministry / Government
Press officer
Others
Outbreak
Investigation
Team?
Assess situation
Examine available information
Preliminary hypothesis ?
Case definition
Case finding
Descriptive epidemiology
WHO/CSR
Case definition
• Standard set of criteria for deciding if a
person should be classified as suffering
from the disease under investigation.
• Clinical criteria, restrictions of time, place,
person
• Simple, practical, objective
• Sensitivity versus specificity
WHO/CSR
Case definition: example
Patient older than 5 years with severe
dehydration or dying of acute watery
diarrhoea in town “x” between 1 June
and 20 July 1998
WHO/CSR
Case definition: categorisation
• Possible
– Patient with severe diarrhoea
• Probable
– Patient older than 5 years with severe
dehydration or dying of acute watery
diarrhoea in town “x” between 1 June
and 20 July 1998
• Confirmed
– Isolation of Vibrio cholerae from stool of
patient
WHO/CSR
Identify &
count cases
Clearly identifiable groups
Hospitals
Laboratories
Schools
Workplace, etc
Obtain information
Perform descriptive
epidemiology
WHO/CSR
Identify &
count cases
Obtain
information
Identifying information
Demographic information
Clinical details
Risk factors
Perform descriptive
epidemiology
WHO/CSR
Identify &
count cases
Obtain
information
Perform descriptive
epidemiology
Orient cases in
- time
- place
- person
WHO/CSR
Cases
Time
Person
1000
Place
800
600
400
200
0
20
18
16
14
12
10
8
6
4
2
0
1
0-4
'15-44
2
3
4
5
6
7
8
9
'64+
Age Group
Evaluate information
Pathogen?
Source?
WHO/CSR
Transmission?
10
Cases of viral meningitis by date of admission (n=416)
Cyprus, 5 July - 5 November 5 1996
25
Cases
20
15
10
5
0
5
11 17 23 29 4 10 16 22 28 3
9
July
August
September
15 21 27 3
October
Date of admission
9
15 21 27
November
WHO/CSR
2
Point source
25
Examples of
epidemic curves
20
15
10
5
0
1
Continuing common source
20
3
5
7
9 11 13 15 17 19
Multiple waves -person to person
or further outbreak
20
15
15
10
10
5
5
0
1
3
5
7
9 11 13 15 17 19
0
1
3
5
7
9
WHO/CSR
11 13 15 17 19
Admissions per 100,000 population for viral meningitis
by age group. Cyprus, 5 July - 5 November 1996
500
Admissions/100,000 pop
450
400
350
300
250
200
150
100
50
0
0-4
5-9
10-14 15-19 20-24 25-29 30-34 35-39 40-44 45+
Age Group
WHO/CSR
Admissions per 100,000 population for viral meningitis
by district; Cyprus, 5 July - 5 November 1996
Nicosia
F. Famagusta
Paphos
Larnaca
Limassol
Cases per 100,000
1-49
50-99
100 +
No data
WHO/CSR
Confirmed cases of meningococcal meningitis
type B by residence, Dublin, 1996
8
1 dot = 1 case
6
7
5
3
4
1
2
9
10
WHO/CSR
Develop hypotheses
• Who is at risk of becoming ill?
• What is the disease causing the
outbreak?
• What is the source and the vehicle?
• What is the mode of transmission?
Compare hypotheses with facts
WHO/CSR
Test specific hypotheses
Analytical epidemiological studies
Cohort
Case-control
WHO/CSR
Implement control measures
May occur at any time
during the outbreak!!
Control the source of the pathogen
Interrupt transmission
Modify host response
Prevent recurrence
WHO/CSR
Control the source of pathogen
• Remove source of contamination
• Remove persons from exposure
• Inactivate / neutralise the pathogen
• Isolate and/or treat infected persons
WHO/CSR
Interrupt transmission
• Interrupt environmental sources
• Control vector transmission
• Improve personal sanitation
WHO/CSR
Modify host response
• Immunise susceptibles
• Use prophylactic chemotherapy
WHO/CSR
Source/Transmission
known
unknown
Investigation +
Investigation +++
Control +++
Control +
Investigation +++
Investigation +++
Control +++
Control +
WHO/CSR
Source: Goodman 1990
At the end
• Prepare written report
• Communicate public health messages
• Influence public health policy
• Evaluate performance
WHO/CSR
Thank you
WHO/CSR