This document outlines the steps for investigating an outbreak, including how outbreaks are recognized, why they should be investigated, and the epidemiological investigation process. It describes the 10 key steps in an outbreak investigation: 1) confirming the outbreak, 2) verifying diagnoses, 3) preparing for field work, 4) defining a case definition, 5) identifying and listing cases, 6) performing descriptive epidemiology, 7) generating hypotheses, 8) testing hypotheses, 9) implementing control measures, and 10) communicating findings. The goal of an outbreak investigation is to uncover public health problems, identify risk factors, prevent future outbreaks, and train health staff.

1. 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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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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Jordan-FETP 1999-2009
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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Name Age Gender Date and
time of
onset
Symptom
1
Abdomin
al pain
Symptom
2
Fever
Symptom
3
Diarrhea
Adress Group
event
Outcome
Ahmad 23 male 8/9/2010
2 pm
yes no yes yes Hospitaliz
ation
Fatima 15 female 7/9/2010
10 am
no yes yes no i.v fluids
Kamal 8 male 7/9/2010 yes yes yes yes Hospitaliz
ation
Omar 34 male 6/9/2010 no yes yes yes ORS
Layla 37 female 8/9/2010
7 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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THANK YOU
Jordan FETP 2009-2011