Outbreak investigation, response and control

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Outbreak investigation, response and control

• Integrated Disease Surveillance Programme (IDSP)
  district surveillance officers (DSO) course

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Preliminary questions to the group

• What is your experience in outbreak
  investigations?
• If yes, what difficulties did you face?
• What would you like to learn about outbreak
  investigations?

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Outline of the session

1. Outbreaks and epidemics
2. Outbreak detection
3. Outbreak investigation
4. Managerial aspects of outbreak investigations

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Endemic versus epidemic

• Endemicity
• Disease occurring in a population regularly at a
  usual level
• Tuberculosis, Malaria
• Epidemics
• Unusual occurrence of the disease in excess of
  its normal expectation
• In a geographical location
• At a given point of time
• e.g. Hepatitis E, measles, cholera

Outbreaks
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Outbreaks versus epidemics

• Occurrence of cases of an illness in excess of
  expected numbers
• Scale
• Outbreak
• Limited to a small area, within one district or
  few blocks
• Epidemic
• Covers larger geographic areas
• Linked to control measures in district/state
• No exact precise threshold Use a word or the
  other according to whether you want to generate
  or deflect attention
• Be aware of legal implications of the use of the
  term Epidemic in India (Epidemic disease act,
  being revised)

Outbreaks
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Sources of information to detect outbreaks

• Event-based surveillance
• Rumour register
• To be kept in standardized format in each
  institution
• Rumours need to be investigated
• Community informants
• Private and public sector
• Media
• Important source of information, not to neglect
• Case-based surveillance
• Review of routine surveillance data and triggers

Detection
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Early warning signals for an outbreak

• Clustering of cases or deaths
• Increases in cases or deaths
• Single case of disease of epidemic potential
• Acute febrile illness of an unknown etiology
• Two or more linked cases of disease with outbreak
  potential
• (e.g., Measles, Cholera, Dengue, Japanese
  encephalitis or plague)
• Unusual isolate (Cholera O 139)
• Shifting in age distribution of cases (Cholera O
  139)
• High vector density
• Natural disasters

Detection
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Importance of timely action The first
information report (Form C)

• Filled by the reporting unit
• Submitted to the District Surveillance Officer as
  soon as the suspected outbreak is verified
• Sent by the fastest route of information
  available
• Telephone
• Fax
• E-mail

Detection
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The rapid response team

• Composition
• Epidemiologist, clinician and microbiologist
• Entomologist when vector-borne disease
• Gathered on ad hoc basis when needed
• Role
• Confirm and investigate outbreaks
• Responsibility
• Assist in the investigation and response
• Primary responsibility rests with local health
  staff

Detection
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Objectives of an outbreak investigation

1. Verify
2. Recognize the magnitude
3. Diagnose the agent
4. Identify the source and mode of transmission
5. Formulate prevention and control measures

Investigations
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The balance between investigation and control
while responding to an outbreak
Source / transmission Source / transmission
Known Unknown
Etiology Known Control Investigate Control Investigate
Etiology Unknown Control Investigate Control Investigate
Investigations
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Steps in outbreak response

1. Verifying the outbreak
2. Sending the rapid response team
3. Monitoring the situation
4. Declaring the outbreak over
5. Reviewing the final report

Investigations
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Step 1 Verifying the outbreak

• Validate the source of information
• Change in the reporting system
• Change in the population size
• Acute reporting of old, chronic cases
• Check with the concerned medical officer
• Abnormal increase in the number of cases
• Clustering of cases
• Epidemiological link between cases
• Triggering event
• Deaths

Investigations
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Step 2 Sending the rapid response team

• Review if the source and mode of transmission are
  known
• If not, constitute team with
• Medical officer
• Epidemiologist
• Laboratory specialist
• Formulation of hypothesis on basis of the
  description by time, place and person
  (Descriptive epidemiology)
• Does the hypothesis fits the fact
• YES Propose control measures
• NO Conduct analytical studies

Investigations
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Investigating an outbreak
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Example Outbreak of acute hepatitis (E) in
Baripada, Orissa, 2003

• Identification of a cluster of acute hepatitis
  cases
• Diagnosis HEV infection
• Use time, place and person analysis of
  surveillance data to suggests hypotheses

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Cases of acute hepatitis (E) by date of onset,
Baripada, January-March 2004
Time A cluster a month after a strike in the
water treatment centre
Investigation
45
started
Cases
40
Deaths
35
Strike among municipal Workers Water treatment
stopped
30
25
Number of cases and deaths
20
15
10
5
0
3/1/04
1/1/04
1/3/04
1/5/04
1/7/04
1/9/04
2/2/04
2/4/04
2/6/04
2/8/04
3/3/04
3/5/04
3/7/04
1/11/04
1/13/04
1/15/04
1/17/04
1/19/04
1/21/04
1/23/04
1/25/04
1/27/04
1/29/04
1/31/04
2/10/04
2/12/04
2/14/04
2/16/04
2/18/04
2/20/04
2/22/04
2/24/04
2/26/04
2/28/04
Investigations
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Attack rate of acute hepatitis (E) by residence,
Baripada, Orissa, India, 2004
Place Highest rates next to the pump taking
water from river bed
Attack rate
0 - 0.9 / 1000
1 - 9.9 / 1000
10 -19.9 / 1000
20 / 1000
Chipat river
Investigations
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Attack rate of acute hepatitis (E) by age and
sex, Baripada, Orissa, India, 2004
Person Attack rate compatible with HEV
Cases Population Attack rateper 1000
Age 0-4 1 1012 0.1
5-9 11 21802 2
10-14 37 74004 5
15-44 416 51358 81
45 73 56153 13
Sex Male 341 102683 3.3
Female 197 101646 1.9
Investigations
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What hypotheses would you generate for the
outbreak of acute hepatitis (E) in Baripada,
Orissa, 2003?

• Time
• It happens a month after a strike in the water
  treatment plant
• Place
• It is clustered around a water source that takes
  water from the river
• Person
• Adults are mostly affected

The river water may have been supplied untreated
in the area of the outbreak because of the strike
at the water treatment plant
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Descriptive versus analytical investigations

• Descriptive investigations
• Based upon cases only
• Look at time, place and person epidemiology
• Raise hypotheses
• Analytical investigations
• Based upon a study of the cases and non-cases
• Compare
• Cases with controls with respect to exposure
• Exposed with unexposed with respect to incidence
• Test hypotheses
• How could we test the hypothesis for the Baripada
  investigation?

Investigations
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Steps of a full outbreak investigation using
analytical epidemiology to identify the source of
infection

• Determine the existence of an outbreak
• Confirm the diagnosis
• Define a case
• Search for cases
• Generate hypotheses using descriptive findings
• Test hypotheses based upon an analytical study
• Draw conclusions
• Compare the hypothesis with established facts
• Communicate findings
• Execute prevention measures
• Requires assistance from qualified field
  epidemiologist (FETP)

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Consumption of pipeline water among acute
hepatitis (E) cases and controls, Baripada,
Orissa, India, 2004
Acute hepatitis Control Total
Drunk water from river bed pump 493 134 627
Did not drink pump water 45 404 449
Total 538 538 1076
92 of cases (493/538) drunk water from
suspected source versus 25 (134/538) of controls
Analytical epidemiology compares cases and non
cases or exposed versus unexposed to test the
hypothesis generated on the basis of the time,
place and person description
Investigations
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3. Monitoring the situation

• Trends in cases and deaths
• Implementation of containment measures
• Stocks of vaccines and drugs
• Logistics
• Communication
• Vehicles
• Community involvement
• Media response

Investigations
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4. Declaring the outbreak over

• Role of the district surveillance officer /
  Medical health officer
• Criteria
• No new case during two incubation periods since
  onset of last case
• Implies careful case search to make sure no case
  are missed

Investigations
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5. Review of the final report

• Sent by medical officer of the primary health
  centre to the district surveillance officer /
  medical and health officer within 10 days of the
  outbreak being declared over
• Review by the technical committee
• Identification of system failures
• Longer term recommendations

Investigations
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Outbreak preparedness A summary of preparatory
action

• Formation of rapid response team
• Training of the rapid response team
• Regular review of the data
• Identification of outbreak seasons
• Identification of outbreak regions
• Provision of necessary drugs and materials
• Identification and strengthening appropriate
  laboratories
• Designation of vehicles for outbreak
  investigation
• Establishment of communication channels in
  working conditions (e.g., Telephone)

Management
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Managerial aspects of outbreak response

• Logistics
• Human resources
• Medicines
• Equipment and supplies
• Vehicle and mobility
• Communication channels
• Information, education and communication
• Media
• Daily update

Management
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Control measures for an outbreak

• General measures
• Till source and route of transmission identified
• Specific measures, based upon the results of the
  investigation
• Agent
• Removing the source
• Environment
• Interrupting transmission
• Host
• Protection (e.g., immunization)
• Case management

Management
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Take home messages

• Do not ignore or hide outbreaks
• Respond to early warning signals
• Investigate outbreaks to
• Control the current outbreak
• Learn about the disease in the local setting
• Outbreaks require an organized, well managed
  response

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Additional reading

• CDC text book on principles of epidemiology
• Section 5 of operations manual
• Module 8 of training manual

Detection