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.
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Fetp outbreak i
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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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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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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Jordan-FETP 1999-2009
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