Outbreak investigation, response and control

Integrated Disease Surveillance Programme (IDSP) district surveillance

officers (DSO) course

2

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 detection3. Outbreak investigation4. 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 agent4. Identify the

source and mode of transmission

5. Formulate prevention and control measures

Host

Environment Agent

An outbreak comes from a change in the way the host, the environment

and the agent interact: This interaction needs to be understood

to propose recommendationsInvestigations

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The balance between investigation and control while responding to an

outbreakSource / transmission

Known Unknown

Etiology

Known Control +++Investigate +

Control +

Investigate +++

Unknown Control +++Investigate +++

Control +

Investigate +++

Investigations

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Steps in outbreak response

1. Verifying the outbreak2. Sending the rapid response team3. Monitoring the situation4. Declaring the outbreak over5. 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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Yes-> Control measures

Hypothesis fit the facts:-> Control measures

Hypothesis does not fit the facts:-> Analytical investigations

Time, place person descriptionFormulation of hypothesis

No-> Clinical, microbiological

and epidemiological investigation

Yes-> Are the source andmodes of transmission

known?

No

Unusual event:Is this an outbreak?

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

Deaths

Investigation

started

Strike among municipal

Workers: Watertreatment stopped

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

Investigations

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Chipat river

Attack rate of acute hepatitis (E) by residence, Baripada,

Orissa, India, 2004

0 - 0.9 / 1000

1 - 9.9 / 1000

10 -19.9 / 1000

20+ / 1000

Attack rate

Underground water supply

Pump from river bed

Place: Highest rates next to the pump taking water from river bed

Investigations

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Attack rate of acute hepatitis (E) by age and sex, Baripada,

Orissa, India, 2004Cases Populatio

nAttack rate

per 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

Person: Attack rate compatible with HEV

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 infection1. Determine the existence of an outbreak2. Confirm the diagnosis3. Define a case 4. Search for cases5. Generate hypotheses using descriptive findings6. Test hypotheses based upon an analytical study7. Draw conclusions8. Compare the hypothesis with established facts9. Communicate findings10. Execute prevention measures

Requires assistance from qualified field epidemiologist (FETP)

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Acute hepatit

isControl Total

Drunk water from river bed pump

493 134 627

Did not drink pump water 45 404 449

Total 538 538 107692% of cases (493/538) drunk water from

suspected source versus 25% (134/538) of controls

Consumption of pipeline water among acute hepatitis (E)

cases and controls, Baripada, Orissa, India, 2004

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

1. Do not ignore or hide outbreaks 2. Respond to early warning signals3. Investigate outbreaks to:

Control the current outbreak Learn about the disease in the local

setting

4. 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