Jordan Field Epidemiology Training Program

Outbreak Investigation

Dr Ghazi Sharkas

Jordan FETP (2009-2011)

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Jordan-FETP 1999-2009

How outbreaks are recognized

The occurrence of an unusual disease, or an unusual number of cases of a disease

By revision of the ordinary surveillance data By the patients or their relatives Rumors Some outbreaks are recognized through

newspapers, television news, or Police departments

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Jordan-FETP 1999-2009

Why to investigate an outbreak

Uncover a much more serious public health problem

Identify risk factors associated with infection under study, that can be preventable

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Jordan-FETP 1999-2009

Why to investigate an outbreak

Increasing knowledge of disease:

Help Preventing future outbreaks

Provide a base line for research about the disease under investigation

Opportunities for training of health staff on problem investigation and rapid response

Cont…

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Jordan-FETP 1999-2009

What to do after outbreak detection

Epidemiological investigation

Environmental investigations

Interaction with the public, the media and sometimes the legal authorities

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Epidemiological outbreak investigation

steps

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1. Confirm the existence of the outbreak

Compare with Baseline surveillance data Data from local sources, neighboring areas

or national data lab diagnosis of the pathogen

Apply immediate control measures if the source is obviously defined

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2. Verify the diagnosis

Rule out laboratory error

Interview / examine case patients

Review medical records

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3. Prepare for field work Compose a team and distribute roles Put an action plan Take all required facilities

1. Ice bags

2. Necessary lab utensils

3. Laptop

4. Sample questionnaires

5. Other supplies

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4. State a case definition using

– Symptoms or lab results

– When (time frame)

– Who's affected (person)

– Where (place)

Categorize case definition, suspected, probable, confirmed

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5.Case identification and line listing

Case finding according to case definition

Collect data on case patients

Arrange data into line listing

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What to include in a line listing

Components of case definition Case name Date of symptom onset Demographic variables(age, occupation) Relevant risk factors

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Jordan-FETP 1999-2009

Name Age Gender Date and time of onset

Symptom1Abdominal pain

Symptom2Fever

Symptom3Diarrhea

Adress Group event

Outcome

Ahmad 23 male 8/9/20102 pm

yes no yes yes Hospitalization

Fatima 15 female 7/9/201010 am

no yes yes no i.v fluids

Kamal 8 male 7/9/2010 yes yes yes yes Hospitalization

Omar 34 male 6/9/2010 no yes yes yes ORS

Layla 37 female 8/9/20107 pm

yes yes no no nothing

Example of a line listing

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6.Perform descriptive epidemiology

Characterize the cases by Time: epidemic curve, when become ill Place: spot map, where the infection

acquired, address Person: who was infected, what cases

have in common (tables)

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Importance of descriptive epidemiology

Describe clinical features of the illness Describe demographic characteristics of

affected persons Identify population at risk Provide clues to etiology, and mode of

transmission Guide interventions

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7. Generate a hypothesis

guided by: Literature review Information from previous outbreaks Nature of suspected pathogen Interviews with case patients Local health officials opinion

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8. Test hypotheses

Current hypotheses may give a clue to the source of the outbreak

Compare with known facts

Conduct further studies if required (retrospective cohort, case control)

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Which study to conduct

Retrospective cohort:

Done for well defined relatively small population, every one is included, calculate and compare attack rates (relative risk)

Case-control:

Done for larger population, controls selection is crucial, calculate odds ratio

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9. Implement control measures

Take control measures as early as possible in order to:

Eliminate the source Interrupt transmission Reduce susceptibility

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9. Implement control measures

Control measures are guided by the results of epidemiological investigation and sometimes environmental specimens

Control measures should be carefully implemented and justified especially if closure of restaurants and institutions is included

Cont…

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10. Communicate findings

Communicate findings through dissemination of summary investigation and recommendations for control to the public and the press

Communication helps to: Document your findings Justify your recommendations and control

measures Protect against legal issues

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Jordan-FETP 1999-2009

THANK YOU

Jordan FETP 2009-2011