laboratory training for field epidemiologists planning a strategy for laboratory investigations...
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E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning a Strategy for
Laboratory Investigations
Adapted sample taking
May 2007
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Learning objectivesLearning objectives
At the end of the presentation, participants should understand :
• Strategies for laboratory analysis
• Rationale to engage the laboratory early
• How to formulate objectives for laboratory analysis
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning an Epidemiologic Planning an Epidemiologic InvestigationInvestigation
Formulate Objectives
Plan Data Analysis
Develop Data
Collection Instruments and Sampling Strategy
Collect Data
Analyze Data
Interpret Data Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning a Laboratory InvestigationPlanning a Laboratory Investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning a Collaborative InvestigationPlanning a Collaborative Investigation
Formulate Objectives
Plan
Prepare
Analyse
Interpret Results and Draw Conclusions
Collect
Data needs
Instruments and Sampling Strategy
Data
DataLab needs
Sampling strategy
Specimens
Specimens
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Why Plan?Why Plan?• Laboratory requirements relate to investigation
objectives
• confirm a diagnosis to document an infection?
• document a common source?
• provide information to help clinical management (antibiotic resistance)?
• What laboratory tests help answer the objective(s)?
• What specimens are required for the laboratory test(s)?
• What’s the sampling strategy?
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning the laboratory InvestigationPlanning the laboratory Investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Define objectives Define objectives
Consider the scope
• public health intervention (e.g. surveillance, outbreak)
• research (e.g. serological survey)
Identify investigative objective
• test a hypothesis (e.g. diagnostic test) (Qualitative)
– fewer specimens needed
• measure (e.g. incidence) (Quantitative)
– may require specimens from all subjects (e.g. cohort study)
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Confidentiality and ConsentConfidentiality and Consent
Public health investigations vs Research Studies
• public health investigation: designed to understand a health event in order to make immediate control and prevention recommendations
Considerations:
• type of specimens required (consider invasiveness)
• need for ethical committee review (time consuming)
• usually not required for public health investigations
• type of consent (verbal, written) (adults, children)
• labelling of specimens (nominal, unique identifiers)
• personal identifiers (how will link to epidemiologic data)
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Ethical considerations Ethical considerations
Investigating a case of acute flaccid paralysis in a polio endemic area
• public health intervention
• nominal specimen (confidentiality)
• verbal consent (no ethics review committee clearance needed)
Investigating possible polio-virus shedding among immunosuppressed subjects in Europe
• research study
• use of unique (non-nominal) identifiers
• ethics review committee required, written informed consent
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning the laboratory investigationPlanning the laboratory investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Laboratory Involvement Laboratory Involvement in the Field in the Field
• Presence in the field ideal
• Can provide timely input based on direct involvement and observation
• time consuming, expensive• most useful in complex investigations, unusual clinical
presentations, unknown pathogens,
• Remote participation as part of outbreak team (more common)
• optimal value if involved early
• need to exchange appropriate, sufficient information
• efficient for routine investigations (known, common pathogens)
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Communicating with the Laboratory Communicating with the Laboratory
• Share initial information early
• time, place and person characteristics
• suspect pathogens
• Ensure on-going communication
• identify focal person, obtain contact information
• generate outbreak number
• provide updates
• send epidemiological report for input/revisions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning the laboratory investigationPlanning the laboratory investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Which specimens to collect?Which specimens to collect?
1. What are the suspected pathogens?
2. What tests are available to identify the suspected pathogens?
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Which specimens to collect?Which specimens to collect?
1. What are the suspected pathogens?
• what is the clinical syndrome?
• what are the epidemiological characteristics?
• what are the macroscopic characteristics of the specimen?
• what infections are endemic in the geographical area?
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Which specimens to collect?Which specimens to collect?
2. What tests are available to identify the suspected pathogens?
• what specimens are required for these tests?
• consult the laboratory
• review guides and references
• which laboratory can do the test?
• consider bio-level, geography, timelines
• consult the laboratory
• activate the network
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Typical scenarioTypical scenario• Typical clinical syndrome
• most cases meet a classical case definition
• Typical epidemiological characteristics
• transmission pattern (e.g. incubation period) compatible with clinical picture
• Typical macroscopic appearance of the specimen
• cloudy cerebro-spinal fluid, rice water diarrhoea
• Endemic area
• cholera in Bengal, meningitis in the Sahel
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Sampling strategy: typical scenarioSampling strategy: typical scenario
• Seeking laboratory confirmation
• one or few key laboratory tests
• one key specimen
• measles virus IgM on serum
• cholera culture on rectal swab
• Use routine procedures
• standard collection and transport procedures
• first level laboratory
• know your counterparts in the laboratory
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Unusual scenarioUnusual scenario
• Atypical presentation
• severe cases (e.g. fatal influenza-like illness)
• Unusual epidemiological characteristics
• unknown or unusual mode of transmission
• Non-compatible macroscopic appearance of the specimen
• Non-endemic area
• cholera in Latin America in early 1990’s
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Sampling strategy: Unusual scenario Sampling strategy: Unusual scenario
• Look for a wide range of pathogens - seek advice from laboratory
• Short-list pathogens on the basis of:
• clinical picture
• epidemiological characteristics
• geographical location
• macroscopic appearance of the specimen
• Consider more than one type of test (e.g. culture, serology)
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Sampling strategy: Unusual scenarioSampling strategy: Unusual scenario
• Examine more than one type of specimen (e.g. blood, urine, stools)
• pathogen might be present in an apparently unaffected organ (e.g. Legionella requires a urine sample)
• Get help
• plan for storage, packaging and transport
• use reference laboratories
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Assess the situation Assess the situation
• Unusual situations may be due to:
• unusual presentation of an common pathogen
• emerging pathogen not usually seen in the area
• emergence of new pathogens• SARS, avian influenza, hantavirus
• Balance need for simplicity with risk of missing serious events
• seek input from all disciplines for decision-making
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Cluster of febrile rash* Cluster of febrile rash* (Middle East)(Middle East)
Suspect pathogen Measles Virus
Possible tests Measles IgM ELISA virus isolation?
Specimens needed acute serum urine sample?
Laboratories to use district laboratory reference laboratory?
*consistent with measles case definition
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Cluster of febrile neurological syndrome Cluster of febrile neurological syndrome (Uttar Pradesh, India)(Uttar Pradesh, India)
Suspect pathogens Bacterial meningitis Japanese encephalitis
Enterovirus encephalitis
Proposed tests CSF - bacteriology serology serology (serum, CSF)
culture (stool, CSF)
Specimens needed CSF acute and convalescent
serum
acute and convalescent
serum
stool and CSF
Laboratories to use district laboratory state laboratory
national laboratory
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
How to select the laboratoryHow to select the laboratory
• Location
• Referral protocols
• Capacity
• Biosafety level
• Quality, accreditation or certification (e.g., Polio)
• Credibility, track record
• Costs
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning the laboratory investigationPlanning the laboratory investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Who to sample?Who to sample?Cases
• “typical” cases
• cases likely to carry the pathogen (e.g. children)
• untreated patients (e.g. without antibiotics)
• outliers (e.g. demographic, geographic)
Controls
• laboratory controls to check that the test is indeed negative
• controls from a case-control study to check to confirm diagnosis (not infected)
All subjects or a representative sample?
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
When to sample?When to sample?
• Once
• acute or convalescent phase • depends on disease
• blood culture first, then serology (typhoid)• depends on symptoms
• fever spikes (e.g. malaria, septicaemia)
• Twice
• acute and convalescent serum
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
How many specimens to collect?How many specimens to collect?
• Ensure sufficient number of specimens (at least 20)
• avoid sampling error
• obtain reliable results
• Repeat sampling
• acute and convalescent sera
• intermittent shedding (e.g. stool microscopy for parasites, bacterial endocarditis)
• explore chronic carriage
• unknown etiology
• Avoid overwhelming the laboratory
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Rule of thumb: cholera outbreakRule of thumb: cholera outbreak
• 10 samples to confirm the outbreak
• Five samples per week during the outbreak
• Samples at the end to confirm that the outbreak is over
Source: WHO
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning the laboratory investigationPlanning the laboratory investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Analyze specimensAnalyze specimens
• Based on epidemiological information, objectives and laboratory consults
• determine ideal testing algorithms
• select tests:
• screening
• confirmatory
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Testing algorithm Testing algorithm
• Standardizes and documents the approach and is:
• essential for quantitative studies • defines what to count
• adapted to the investigation objectives
• agreed upon by epidemiologists and the laboratory
• Takes into account the
• need for information
• need to optimize resources (cost, staff time)
• Must be flexible for qualitative studies
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Testing algorithm: Testing algorithm: Hepatitis B Virus outbreak Hepatitis B Virus outbreak
Recent infection
Positive
Chronic infection
Negative
IgM anti-HBc(Test for recent infection)
Positive
Natural immunity
Negative
HBsAg(Test for current infection)
Positive
Absence of infection
Negative
Total Anti-HBc(Test for exposure to HBV)
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Testing Algorithm: HBV OutbreakTesting Algorithm: HBV Outbreak
• Variations are possible to explore:
• vaccine-induced reactions
• fulminant infection with negative HBsAg test
• Final decisions are a consensus between
• epidemiologists
• laboratory
• The algorithm may help case management
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Source: WHO
Testing Testing Algorithm: HIVAlgorithm: HIV
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Planning the laboratory investigationPlanning the laboratory investigation
Formulate Objectives
Plan Laboratory Analysis
Determine Sampling Strategy
Collect Specimens
Analyze Specimens
Interpret Tests Draw Conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Reporting resultsReporting resultsNeed to clarify from the start:
• When will the results be ready?
• Who will help interpret the results?
• Who will produce the report? Who is the lead?
• How will sensitive information will be handled?
• To whom will the results will be reported and not reported?
• careful with media-sensitive issues (e.g. cholera)
• Who will sign-off the final report?
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Integrating laboratory dataIntegrating laboratory data
• Epidemiologic debrief should include the laboratory
• enables interpretation of epidemiological results in light of the laboratory evidence
• Review should include:
• interpretation - what can be concluded
• limitations – explains why some things cannot be concluded
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
A multi-state outbreak of Hepatitis A among school A multi-state outbreak of Hepatitis A among school children, USA 1997: Resultschildren, USA 1997: Results
State Epidemiological results Laboratory results
Michigan Two clusters in two cities
Hepatitis associated with consumption of frozen strawberries in two epidemiological studies
Indistinguishable Hepatitis A virus
Maine Cases scattered in the state
Borderline association between hepatitis and consumption of frozen strawberries
Hepatitis A virus indistinguishable from the Michigan virus
Arizona Handful of cases having eaten frozen strawberries
Hepatitis A virus indistinguishable from the Michigan and Maine virus
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
A multi-state outbreak of Hepatitis A among school A multi-state outbreak of Hepatitis A among school children, USA 1997: Conclusionschildren, USA 1997: Conclusions
• This multi-state outbreak was caused by the consumption of the same frozen strawberries among school children
• Michigan - the epidemiological information is sufficient to conclude this
• Maine - the laboratory evidence supports the less conclusive epidemiological evidence
• Arizona - few cases; only the laboratory evidence allows this conclusion
• The smaller number of cases in Maine and Arizona may reflect a lower level of contamination of the product distributed in these two states
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Take home messagesTake home messages
• Frame objectives with the end (public health action) in mind
• Engage the laboratory early
• Create sampling strategy consistent with your objectives
• Collect only as many specimens as you need – don’t overdo it
• Create the analytical strategy
• Put all laboratory and epidemiology pieces together to draw conclusions
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
Adapted sample taking
Developed by the Department of Epidemic and Pandemic Alert and Response of the World Health Organization with assistance from:
European Program for Intervention Epidemiology Training
Canadian Field Epidemiology Program
Thailand Ministry of Health
Institut Pasteur
E P I D E M I C A L E R T A N D R E S P O N S E Laboratory Training for Field Epidemiologists
ReferencesReferences
Slide 37
• Source: Rapid HIV tests: Guidelines for use in HIV testing and counselling services in resource-constrained settings WHO 2004