Planning a Strategy for Laboratory Investigations

Adapted sample taking Planning a Strategy for Laboratory Investigations May 2007

Learning 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

Planning an Epidemiologic Investigation Formulate Objectives Interpret Data Draw Conclusions Plan Data Analysis Analyze Data Collect Data Develop Data Collection Instruments and Sampling Strategy

Planning a Laboratory Investigation Formulate Objectives Interpret Tests Draw Conclusions Plan Laboratory Analysis Analyze Specimens Collect Specimens Determine Sampling Strategy

Planning a Collaborative Investigation Formulate Objectives Interpret Results and Draw Conclusions Plan Analyse Lab needs Specimens Data needs Data Prepare Collect Instruments and Sampling Strategy Specimens Sampling strategy Data

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?

Planning the laboratory Investigation Formulate Objectives Interpret Tests Draw Conclusions Plan Laboratory Analysis Analyze Specimens Collect Specimens Determine Sampling Strategy

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)

Confidentiality 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)

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

Planning the laboratory investigation Formulate Objectives Interpret Tests Draw Conclusions Plan Laboratory Analysis Analyze Specimens Collect Specimens Determine Sampling Strategy

Laboratory Involvement 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)

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

Which specimens to collect? • What are the suspected pathogens? • What tests are available to identify the suspected pathogens?

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?

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

Typical 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

Sampling 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

Unusual 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

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)

Sampling 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

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

Cluster of febrile rash* (Middle East) *consistent with measles case definition

Cluster of febrile neurological syndrome (Uttar Pradesh, India)

How to select the laboratory • Location • Referral protocols • Capacity • Biosafety level • Quality, accreditation or certification (e.g., Polio) • Credibility, track record • Costs

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?

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

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

Rule 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

Analyze specimens • Based on epidemiological information, objectives and laboratory consults • determine ideal testing algorithms • select tests: • screening • confirmatory

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

Testing algorithm: Hepatitis B Virus outbreak

Testing 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

Testing Algorithm: HIV Source: WHO

Reporting results Need 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?

Integrating 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

A multi-state outbreak of Hepatitis A among school children, USA 1997: Results

A multi-state outbreak of Hepatitis A among school children, 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

Take 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

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 Adapted sample taking

References Slide 37 • Source: Rapid HIV tests: Guidelines for use in HIV testing and counselling services in resource-constrained settings WHO 2004

Planning a Strategy for Laboratory Investigations