Outbreak Investigation Tran Minh Nhu Nguyen Technical Adviser WHO Vietnam [email protected].
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Transcript of Outbreak Investigation Tran Minh Nhu Nguyen Technical Adviser WHO Vietnam [email protected].
Outbreak InvestigationOutbreak Investigation
Tran Minh Nhu Nguyen
Technical Adviser
WHO Vietnam
What is an outbreak ?
Occurrence of more cases of disease than expected
– in a given area – over a particular period of time – among a specific group of people
Objectives for this session
• Highlight a systematic approach to outbreak investigation
• Define steps of an outbreak investigation
• Provide an overview of the course content
Scenario• It’s a late Friday afternoon at the local health
department. You were about to leave when the phone rings.
• On the line, a panicked voice explains that there have been 2 patients from a local garment factory admitted to the hospital with severe acute diarrhea, and you need to do something about it.
• You hang up the phone. “Right, right,” you say to yourself, “I need to do something about this problem! PROBLEM?”
• But what should you do?
DAY
Delayedresponse
CASES
Latedetection
First case
Potentiallypreventable cases
Outbreak with timely detection and
response
Outbreak with delayed detection
and response
DAY
CASES
Earlydetection
Potentiallypreventable cases
First case
Promptresponse
Objetives of your investigation
Determine the etiologic agent involved
Determine the potential source
Determine the mode of transmission
Optimize the case management
Interrupt the chain of transmission
Prevent future outbreaks
Investigation must meet these OBJETIVES:
To implement these INTERVENTIONS:
Epidemiology
Food safety
Clinicians
Laboratory
Media AuthoritiesDiagnostic
Clinical
Specimen transfer
Dead Sick
Exposed
SurveillanceInvestigation
Prediction
Supply channels
Trace back
DecisionsInfrastructureRegulationsVaccinations etc
VectorReservoir
Investigation
Co-ordination
Specific demands when investigating outbreaks
• Unexpected event
• Act quickly
• Rapid control
• Interdisciplinary coordination
• Work carried out in the field
Systematic approach
Steps of an outbreak investigation
1. Confirm outbreak and diagnosis2. Form Outbreak Control Team3. Define a case 4. Identify cases and obtain information5. Describe data by time, place, person6. Develop hypothesis7. Test hypothesis: analytical studies 8. Additional studies9. Implement control measures10. Communicate results
Confirm outbreakIs this an outbreak?• More cases than expected?• Surveillance data• Surveys: hospitals, labs, physicians
Caution!• Seasonal variations• Notification artefacts• Diagnostic bias (new technique)• Diagnostic errors (pseudo-outbreaks)
Confirm diagnosis
• Review the clinical findings• Examine some cases• Meet attending physicians• Review the lab findings• Contact the laboratories• Obtain additional lab specimens
Not always necessary to confirm all the casesbut confirm a proportion throughout the outbreak
Outbreak confirmed
Immediate control measures?
Further investigation?
- prophylaxis- exclusion / isolation- public warning- hygienic measures- others
- causative agent- mode of transmission- vehicle of transmission- source of contamination- population at risk- exposure causing illness
EpidemiologistMicrobiologistClinicianEnvironmentalistEngineersVeterinariansOthers
Team coordinatesfield investigation
Outbreak confirmed, further investigations warranted
Form Outbreak Control Team
Descriptive epidemiology
- Who are the cases? (person)
- Where do they live? (place)
- When did they become ill? (time)
Case definition
1.1. PersonPerson2.2. PlacePlace3.3. TimeTime
Epidemiologic Epidemiologic triangletriangle
Standard set of criteria for deciding if a person should be classified as suffering from the disease under investigation
Case definition
• Simple, practical, objective
• Sensitive?
• Specific?
• Multiple case definitions
– confirmed
– probable
– possible
Identify & count cases
Obtain information
Identifying information
Demographic information
Clinical details
Exposures and known risk factors
Organize information: Line list
• Names• Date of birth• Address• Onset of symptoms• Treating physician• Hospital stay• Laboratory results
Identify & count cases
Obtain information
Analysis of descriptive data
Describe in
- time
- place
- person
Time: Epi curve
• Describe– start, end, duration
– peak
– importance
– atypical cases
• Helps to develop hypotheses– incubation period– etiological agent– type of source– type of transmission– time of exposure
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10 11 12
Cases
Days
Examples of Epicurves
0
1
2
3
4
5
6
1 2 3 4 5 6 7 8
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10 11 12
0
2
4
6
8
10
12
1 2 3 4 5 6 7 8 9 10 11 12 13
hours
cases
cases
cases
days
weeks
Common point source Common persistent source
Propagated source
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
cases
days
Common intermittent source
Outbreak of typhoid fever, Dong Thap 2002
5 2
6 3 1 4
15 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
April May
Probable time period of infection
J une
N° c
ases
Shortest incubation period:
Longest incubation period: 60 dayssuspected caseprobable caseconfirmed case
Place
• Place of residence• Place of possible exposure
– work– meals– travel routes, – day-care– leisure activities
• Maps– identify an area at risk
Person
• Distribution of cases – age– sex– occupation, etc
• Distribution of these variables in population • Attack rates
Develop hypotheses
- Who is at risk of becoming ill?
- What is the disease?
- What is the source and the vehicle?
- What is the mode of transmission?
Compare hypotheses with facts
Test specific hypotheses
Analytical studies- cohort studies- case-control studies
Testing hypothesis
• Cohort - attack rate exposed group- attack rate unexposed group
• Case control- proportion of cases exposed- proportion of controls exposed
Verify hypothesisAdditional investigations
• Microbiological investigation of food samples
• Environmental investigation
• Veterinarian investigation
• Molecular Typing
• Trace back investigations (origin of foods)
• Meteorological data
• Entomological investigations
Implement control measures
1) Control the source of pathogen
2) Interrupt transmission
3) Modify host response
May (must) occur at any time during the outbreak!!
At first, general measures
According to findings, more specific measures
Outbreak report
• Regular updates during the investigation
• Detailed report at the end
– communicate public health messages
– influence public health policy
– evaluate performance
– training tool
– legal proceedings
Steps of an outbreak investigation
1. Confirm outbreak and diagnosis2. Form Outbreak Control Team3. Define a case 4. Identify cases and obtain information5. Describe data by time, place, person6. Develop hypothesis7. Test hypothesis: analytical studies 8. Additional studies9. Implement control measures10. Communicate results