WHO/CSR Principles of Outbreak Management. WHO/CSR Definition of outbreak Occurrence of more cases...
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Transcript of WHO/CSR Principles of Outbreak Management. WHO/CSR Definition of outbreak Occurrence of more cases...
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
WHO/CSRWHO/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/CSRWHO/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/CSRWHO/CSR
Is this an outbreak?
Diagnosis verified ? clinical + laboratory
Link between cases?Expected numbers?
DetectionRoutine surveillanceClinical / LaboratoryGeneral publicMedia
WHO/CSRWHO/CSR
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
WHO/CSRWHO/CSR
0
10
20
30
40
50
60
70
80
90
Sequence of events in outbreak detection and confirmation (II)
PRIM HC REP RESSAMPResponse
begins
DAY
CASES
Potential Cases Prevented
WHO/CSRWHO/CSR
Outbreak confirmed
Further investigation?
Immediate control measures?
WHO/CSRWHO/CSR
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?
WHO/CSRWHO/CSR
EpidemiologistMicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers
FIELD
Outbreak Investigation
Team?
WHO/CSRWHO/CSR
Coordination
Epidemiology
Education
Clinicians
Laboratory
Media AuthoritiesDiagnostic
Clinical
Specimen transfer
Dead Sick
Exposed
SurveillanceInvestigation
Prediction
Health personnel
Specialgroups
Generalpopulation
DecisionsInfrastructureRegulationsVaccinations etc
VectorReservoir
WHO/CSRWHO/CSR
Outbreak Investigation
Team?
EpidemiologistMicrobiologistEnvironmental specialistMinistry / GovernmentPress officerOthers
Descriptive epidemiology
Assess situationExamine available information
Preliminary hypothesis ?Case definition
Case finding
WHO/CSRWHO/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/CSRWHO/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/CSRWHO/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/CSRWHO/CSR
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
WHO/CSRWHO/CSR
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?
WHO/CSRWHO/CSR
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
WHO/CSRWHO/CSR
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
WHO/CSRWHO/CSR
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
WHO/CSRWHO/CSR
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
WHO/CSRWHO/CSR
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?
WHO/CSRWHO/CSR
Case-controlCohort
Analytical epidemiological studies
Test specific hypotheses
WHO/CSRWHO/CSR
Implement control measures
May occur at any time during the outbreak!!
Prevent recurrence
Control the source of the pathogen
Interrupt transmission
Modify host response
WHO/CSRWHO/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/CSRWHO/CSR
Interrupt transmission
• Interrupt environmental sources
• Control vector transmission
• Improve personal sanitation
WHO/CSRWHO/CSR
Modify host response
• Immunise susceptibles
• Use prophylactic chemotherapy
WHO/CSRWHO/CSR
Source/Transmission
known unknown
Aet
iolo
gy
kn
ow
nu
nkn
ow
n
Investigation +
Control +++
Investigation +++
Control +
Investigation +++
Control +++
Investigation +++
Control +
Source: Goodman 1990
WHO/CSRWHO/CSR
At the end
• Prepare written report
• Communicate public health messages
• Influence public health policy
• Evaluate performance
WHO/CSRWHO/CSR
Thank you