who/csr principles of outbreak management. who/csr definition of outbreak occurrence of more cases...
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WHO/CSRWHO/CSR
Principles of Outbreak Principles of Outbreak ManagementManagement
WHO/CSRWHO/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/CSRWHO/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
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Specific demands when investigating outbreaks
• Unexpected event• Need to act quickly• Need for rapid control• Work carried out in the field
Systematic approach
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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
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Is this an outbreak?
Diagnosis verified ? clinical + laboratory
Link between cases?Expected numbers?
DetectionRoutine surveillanceClinical / LaboratoryGeneral publicMedia
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0
10
20
30
40
50
60
70
80
90
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
Sequence of Events in outbreak detection and confirmation (I)
PrimaryCase
1st case at HC
Report to DMO
Lab result
Samplestaken
Responsebegins
DAY
CASESOpportunity for control
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0
10
20
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Sequence of events in outbreak detection and confirmation (II)
PRIM HC REP RESSAMPResponse
begins
DAY
CASES
Potential Cases Prevented
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Outbreak confirmed
Further investigation?
Immediate control measures?
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Unknown aetiology(pathogen/source/transmission)Cases seriousCases still occurringPublic pressureTraining opportunity Scientific interest
Outbreak confirmed
Further investigation?
ProphylaxisExclusion / isolationPublic warningHygienic measures
Assistance ?
Immediate control measures?
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EpidemiologistMicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers
FIELD
Outbreak Investigation
Team?
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Coordination
Epidemiology
Education
Clinicians
Laboratory
Media AuthoritiesDiagnostic
Clinical
Specimen transfer
Dead Sick
Exposed
SurveillanceInvestigation
Prediction
Health personnel
Specialgroups
Generalpopulation
DecisionsInfrastructureRegulationsVaccinations etc
VectorReservoir
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Outbreak Investigation
Team?
EpidemiologistMicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers
Descriptive epidemiology
Assess situationExamine available information
Preliminary hypothesis ?Case definition
Case finding
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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
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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
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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
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Identify & count cases
Obtain information
Perform descriptive epidemiology
Clearly identifiable groups
Hospitals
Laboratories
Schools
Workplace, etc
WHO/CSRWHO/CSR
Identify & count cases
Obtain information
Perform descriptive epidemiology
Identifying information
Demographic information
Clinical details
Risk factors
WHO/CSRWHO/CSR
Identify & count cases
Obtain information
Perform descriptive epidemiology
Orient cases in
- time
- place
- person
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Person
Place
Time
Cases
02468
101214161820
1 2 3 4 5 6 7 8 9 100
200
400
600
800
1000
0-4 '15-44 '64+
Age Group
Evaluate information
Pathogen? Source? Transmission?
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Cases of viral meningitis by date of admission (n=416) Cyprus, 5 July - 5 November 5 1996
0
5
10
15
20
25
5 11 17 23 29 4 10 16 22 28 3 9 15 21 27 3 9 15 21 27 2
Date of admission
Cas
es
July August September October November
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0
5
10
15
20
25
1 3 5 7 9 11 13 15 17 19
0
5
10
15
20
1 3 5 7 9 11 13 15 17 190
5
10
15
20
1 3 5 7 9 11 13 15 17 19
Examples of epidemic curves
Point source
Continuing common source Multiple waves -person to person or further outbreak
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Admissions per 100,000 population for viral meningitis by age group. Cyprus, 5 July - 5 November 1996
0
50
100
150
200
250
300
350
400
450
500
0-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45+Age Group
Ad
mis
sio
ns/
100,
000
po
p
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Admissions per 100,000 population for viral meningitis by district; Cyprus, 5 July - 5 November 1996
1-49
50-99
100 +
No data
Cases per 100,000
Nicosia
Paphos
Limassol
Larnaca
F. Famagusta
WHO/CSRWHO/CSR
Confirmed cases of meningococcal meningitistype B by residence, Dublin, 1996
1 dot = 1 case8
67
12
34
5
910
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Develop hypotheses
Compare hypotheses with facts
• 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?
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Case-controlCohort
Analytical epidemiological studies
Test specific hypotheses
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Implement control measures
May occur at any time during the outbreak!!
Prevent recurrence
Control the source of the pathogen
Interrupt transmission
Modify host response
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Control the source of pathogen
• Remove source of contamination
• Remove persons from exposure
• Inactivate / neutralise the pathogen
• Isolate and/or treat infected persons
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Interrupt transmission
• Interrupt environmental sources
• Control vector transmission
• Improve personal sanitation
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Modify host response
• Immunise susceptibles
• Use prophylactic chemotherapy
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Source/Transmission
known unknown
Aet
iolo
gy
kn
ow
nu
nkn
ow
n
Investigation +
Control +++
Investigation +++
Control +
Investigation +++
Control +++
Investigation +++
Control +
Source: Goodman 1990
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At the end
• Prepare written report
• Communicate public health messages
• Influence public health policy
• Evaluate performance
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Thank you