Principles of Outbreak Management

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Principles of Outbreak Management
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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

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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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Routine surveillance Clinical /
Laboratory General public Media
Detection
Is this an outbreak?
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Sequence of Events in outbreak detection and
confirmation (I)
Primary Case
1st case at HC
Report to DMO
Lab result
Samples taken
Response begins
CASES
Opportunity for control
DAY
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Sequence of events in outbreak detection and
confirmation (II)
Response begins
PRIM
HC
REP
RES
SAMP
Potential Cases Prevented
CASES
DAY
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Outbreak confirmed
Further investigation?
Immediate control measures?
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Outbreak confirmed
Further investigation?
Immediate control measures?
Unknown aetiology (pathogen/source/transmission) C
ases serious Cases still occurring Public
pressure Training opportunity Scientific interest
Prophylaxis Exclusion / isolation Public
warning Hygienic measures
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Outbreak Investigation Team?
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Vector Reservoir
Dead
Sick
Surveillance
Investigation
Exposed
Prediction
Clinicians
Epidemiology
Coordination
Education
Laboratory
Clinical
Health personnel
Specimen transfer
Special groups
General population
Diagnostic
Authorities
Media
Decisions Infrastructure Regulations Vaccinations
etc
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Epidemiologist Microbiologist Environmental
specialist Ministry / Government Press
officer Others
Outbreak Investigation Team?
Assess situation Examine 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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Clearly identifiable groups Hospitals Laboratories
Schools Workplace, etc
Identify count cases
Obtain information
Perform descriptive epidemiology
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Identify count cases
Identifying information Demographic
information Clinical details Risk factors
Obtain information
Perform descriptive epidemiology
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Identify count cases
Obtain information
Orient cases in - time - place - person
Perform descriptive epidemiology
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Cases
Time
Person
Place
Evaluate information
Pathogen?
Transmission?
Source?
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Cases of viral meningitis by date of admission
(n416) Cyprus, 5 July - 5 November 5 1996
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Point source
Examples of epidemic curves
Multiple waves -person to person or further
outbreak
Continuing common source
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Admissions per 100,000 population for viral
meningitis by age group. Cyprus, 5 July - 5
November 1996
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Admissions per 100,000 population for viral
meningitis by district Cyprus, 5 July - 5
November 1996
Nicosia
F. Famagusta
Paphos
Larnaca
Limassol
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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
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Test specific hypotheses
Analytical epidemiological studies
Case-control
Cohort
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Implement control measures
May occur at any time during the outbreak!!
Control the source of the pathogen
Interrupt transmission
Modify host response
Prevent recurrence
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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
unknown
known
Investigation Control
Investigation Control
known
Aetiology
Investigation Control
Investigation Control
unknown
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