The EPIET programme Viviane Bremer, EPIET Chief Coordinator.
Outbreak Investigation EPIET Introductory course 2006 Lazareto, Menorca, Spain.
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Transcript of Outbreak Investigation EPIET Introductory course 2006 Lazareto, Menorca, Spain.
Outbreak InvestigationOutbreak Investigation
EPIET Introductory course 2006
Lazareto, Menorca, Spain
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
Why investigate outbreaks?
• Stop the outbreak• Understand what happened and why• Prevent future outbreaks• Improve our knowledge• Improve surveillance and outbreak detection • Training
Objectives for this session
• Describe – the principles of outbreak investigation– the steps in outbreak investigation
• Using practical examples– Outbreak of Hepatitis A in Ibiza, Spain
September 2000 - January 2001
• Tomorrow– some operational and logistical aspects
of outbreak investigation
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
Outbreak of Hepatitis A in Ibiza (Spain) 2000/2001
• Ibiza is a major tourist destination(2 million visitors in 2000)
• 23-27 October 2000: 5 cases of Hepatitis A notified to local health authorities in Ibiza
• 3 cases of Hepatitis A among German tourists returning from Ibiza
Steps of an outbreak investigation
• Confirm outbreak and diagnosis• Form Outbreak Control Team• Define a case • Identify cases and obtain information• Describe data by time, place, person• Develop hypothesis• Test hypothesis: analytical studies • Additional studies• Communicate results:
– outbreak report, publication
• Implement control measures
Co
ntro
l measu
res
Detection
Routine surveillanceClinical / LaboratoryGeneral publicMedia
0
20
40
60
80
100
120
no. cases
2002(n=184)
20052004(n=153)
2003(n=150)
Notified cases of S. Bovismorbificans, Germany 2002-2005
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)
Outbreak of Hepatitis A in Ibiza, Spain
• Hepatitis A notifiable disease in Spain• notifications in Ibiza during previous years:
– 1997: 6 cases– 1998: 0 cases– 1999: 4 cases
Confirm diagnosis
• Laboratory confirmation – serology– isolates, typing of isolates– toxic agents
• Meet attending physicians• Examine some cases• Contact (visit) the laboratories
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
- aetiological 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
• Standard set of criteria for deciding if a person should be classified as suffering from the disease under investigation
• Criteria
– clinical and/or biological criteria,
– time
– place
– person
Case definition
• Simple, practical, objective
• Sensitive?
• Specific?
• Multiple case definitions
– confirmed
– probable
– possible
Case definition Outbreak of Hepatitis A in Ibiza 2000/2001
Any person
• with IgM antibodies to Hepatitis A VirusAugust 2000 - January 2001
• on the island of Ibiza for at least one day during a 15-50 day period before onset of illness or seroconversion
Identify & count cases
notificationshospitals, GPslaboratoriesschoolsworkplace, etc
Case-findingOutbreak of Hepatitis A in Ibiza 2000/2001
• Contacting clinicians and laboratories on the island
• Note in German Epidemiological Bulletin
• Enquiries through European network
Identify & count cases
Obtain information
Identifying information
Demographic information
Clinical details
Exposures and known risk factors
Obtaining informationOutbreak of Hepatitis A in Ibiza 2000/2001
• Trawling questionnaire
• Place and time of stay on Ibiza
• Food histories:
– What eaten
– Where bought?
– Visit to restaurants
Organize information: Line list
• Names• Date of birth• Addresse• Onset of symptoms• Treating physician• Hospital stay• Laboratory results
Line List
Case
No. Name
Date
of birthAddresse
Date of onset
Lab
results
1
2
3
4
5
6
XY
AB
CD
…
…
…
Identify & count cases
Obtain information
Analysis of descriptive data
Describe in
- time
- place
- person
Time: Epi Curve
• Histogram
• Distribution of cases by time of onset
of symptoms, diagnosis or identification– time interval depends on incubation period
Cases
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9 10 11 12
Days
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
cases
10 tourists 9
8 residents76543210
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1
week number
JanuaryDecemberAugust September October November
Cases of Hepatitis A in Ibiza by week of onset, 2000/2001
Estimation of time or period of exposure
0
1
2
3
4
5
6
1 2 3 4 5 6 7 8
max incubation
min
cases
exposure
Outbreak of typhoid fever, Germany 2004
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
June
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
Cases of Hepatitis A in Ibiza by place of residence, 2000/2001
Portinatx
Ibiza-City
10 km
Person
• Distribution of cases – age– sex– occupation, etc
• Distribution of these variables in population • Attack rates
Outbreak of S. Agona, Germany 2003
2003 - Meldungen S. Agona
0
5
10
15
20
25
30
<1 1 2 3 4
5-9
10-1
4
15-1
9
20-2
4
25-2
9
30-3
9
40-4
9
50-5
9
60-6
9
70+
age (years)
No
. Cas
es
20032002 - S. Agona notifications
0
5
10
15
20
25
30
<1 1 2 3 4
5-9
10-1
4
15-1
9
20-2
4
25-2
9
30-3
9
40-4
9
50-5
9
60-6
9
70+
age (years)
No
. cas
es
2002
Cases of Hepatitis A in Ibiza by age group, 2000/2001
0
5
10
15
20
25
0-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59
age (years)
percentage
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?
exploratory interviews among cases of Hepatitis A, Ibiza 2000/01
• 3 potential risk factors:– visited a restaurant in the harbour of Ibiza
town– bought food at a supermarket in the centre
of the town– stayed at Hotel in Portinatx (German
tourists)
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
Case-control study Outbreak of Hepatitis A in Ibiza 2000/2001
• among residents of the island
• one control per case
• selected from the data-base of the health registration card
• matching for age and neighbourhood • no history of hepatitis A disease or
vaccination.
Cases of Hepatitis A and controls by exposure to restaurant and shop,
Ibiza 2000/2001
Exposure Cases (n=38)
Controls (n=38)
matched
OR
95% CI
Restaurant 22 (57.9%) 5 (13.2%) 9.0 2.1-38.8
Shop 13 (34.2%) 6 (15.8%) 4.5 0.97-20.8
Cases of Hepatitis A and controls by exposure to food items, Ibiza 2000/2001
Restaurant
Cases
n = 22
Controls
n = 5
Matched
OR 95% CI
Salad 18 0 undef.
Shop n = 13 n = 6
Sausages 11 3 5.5 0.4-87.3
Meat 10 4 1.67 0.1-21.1
Vegetables 11 4 1.67 0.1-21.1
Fish 9 4 1.13 0.1-12.6
Bread 8 4 0.8 0.1-8.6
Verify hypothesisAdditional investigations
• Microbiological investigation of food samples
• Environmental investigation
• Veterinarian investigation
• Molecular Typing
• Trace back investigations (origin of foods)
• Meteorological data
• Entomological investigations
Viral genome sequencing Outbreak of Hepatitis A in Ibiza 2000/2001
• Alignment of aminoterminal region of VP3
• 38 serum samples
• Positive in 11 cases:
– belonging to the three different groups
– 100% homology
Food trace-back
Schleswig-Holstein
Hamburg
Niedersachsen
Bremen
Nordrhein-Westfalen
Hessen
Rheinland-Pfalz
Baden-Württemberg
Bayern
Saarland
Berlin
Brandenburg
Mecklenburg-Vorpommern
Sachsen
Sachsen-Anhalt
Thüringen
NL
Outbreak of S. Bovismorbificans,
Germany 2004
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
Recommendations Outbreak of Hepatitis A in Ibiza 2000/2001
• Emphasise hygiene amongst food handlers
• Strengthen surveillance for foodborne diseases
• Enhance international co-operation
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
• Confirm outbreak and diagnosis• Form Outbreak Control Team• Define a case • Identify cases and obtain information• Describe data by time, place, person• Develop hypothesis• Test hypothesis: analytical studies • Additional studies• Communicate results:
– outbreak report, publication
• Implement control measures
The reality….
Info:Outbreak suspected
time
Confirmation
Form Outbreak Control Team
Confirm Diagnosis
Site visit
Case definition
Line list
Organize Data
Descripitve Epidemiology
Control measures
AnalyticEpidemiology
Recommendations
ReportPublication