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

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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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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

30

40

50

60

70

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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

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Identify & count cases

Obtain information

Perform descriptive epidemiology

Identifying information

Demographic information

Clinical details

Risk factors

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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

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

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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