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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
Rapid diagnostic tests
Investigation strategies and methods
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 know:
• What a rapid diagnostic test (RDT) is
• When a RDT should be used
• How a RDT should be used
• Who should use a RDT
• Advantages and disadvantages of RDTs
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
Biological confirmationBiological confirmationRequires laboratory with minimal culture, immunoassayequipment
Requires time :
• Bacterial culture : 24-72 hours
• Identification : 4 -24 hours
• Antibiotic susceptibility testing : 24 hours…
• ELISA : 2-4 hours, requires several samples to decrease the cost
Requires trained people
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
Biological confirmationBiological confirmation
In many developing countries, in a epidemic contextrequirements for biological confirmation at peripherallevel is not possible or feasible
Media and political pressure, rumours time is critical
Rapid diagnosis tests can offer a solution
?
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
RDT definitionRDT definition
Results in minutes to 1-2 hours
Accurate, simple to use, low cost, easy to interpret,stable under extreme conditions, little or no processing,culturally acceptable
Include “point of care” (for doctor) and “walk away” tests(home tests)
(Source http://www.rapid-diagnostics.org)
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
MethodsMethods
Antigen detection
Antibody detection
Molecular detection
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
Antigen detectionAntigen detection
Detects bacterial, viral or parasite antigen (surfaceantigen, soluble antigen) or toxin in biological fluids(CSF, blood, urine)
Primary techniques:
• Direct agglutination: slides, cards
• Latex agglutination: slides, cards
• Immunochromatography: dipsticks
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
Latex agglutination testLatex agglutination test
bacterial Ag
Latex beads (= polystyrene particles)
Antibodies specific to Bacterial polysaccharide Ag
Source: WHO meningitis workshop Ouagadougou Sept 2004
Dye-labelled antibody, specific for target antigen, is present on the lower end of nitrocellulose strip or in a plastic well provided with the strip
Antibody, also specific for the target antigen, is bound to the strip in a thin (test) line, and either antibody specific for the labelled antibody, or antigen, is bound at the control line
Source: http://www.wpro.who.int/rdt
Lysing agendLabled AB.
Test band(bound AB)
Control band(bound AB)
Nitrocellulose strip
BoundAB
Free labled AB
http://www.rapid-diagnostics.org/
ImmunochromatographyImmunochromatography
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
Blood and buffer, which have been placed on strip or in the well, are mixed with labelled antibody and are drawn up strip across the lines of bound antibody
Source: http://www.wpro.who.int/rdt
Test band(bound AB)
Control band(bound AB)
Blood and labled Ab flushed along the strip
Parasite antigen (AG.)Captured by labled AB.
ParasitizedBlood
ImmunochromatographyImmunochromatography
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
If antigen is present, some labelled antibody will be trapped on the test line. Excess-labelled antibody is trapped on the control line
Source: http://www.wpro.who.int/rdt
Captured Ag-labled Ab-complex
Captured labled Ab
Labled AB-AG-complexCaptured by bound AB of test band
Labled AB-AG-complexCaptured by bound AB ofcontrol band
Immunochromatography
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
Antibody detectionAntibody detection
Requires seroconversion detection:
• IgG titer elevation not possible with RDT (= qualitative)
• IgM detection (after IgG elimination or IgM capture)
Main techniques:
• Direct agglutination (red cells + antigen, latex + antigen)
• Agglutination inhibition
• Immunodot
• Immunochromatography
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
Molecular detectionMolecular detection
Real-time PCR ?
• DNA extraction < 1 h
• Simultaneous amplification and detection <2 h
• Cost +++
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
Commercialized testsCommercialized tests
Family – genus – species
Bacteria
Clostridium perfringens, Corynebacterium diphteriae, Leptospira interrogans
Mycobacterium tuberculosis, Legionella pneumophila, Neisseria meningitidis
Salmonella Typhi, Yersinia pestis, Vibrio cholerae
Virus Adenovirus, Rotavirus, Influenza virus, Dengue virus, SRV
parasites Plasmodium sp, Giardia lamblia, Cryptosporidium
Not comprehensive
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
Advantages Advantages
Easy to use, minimal training
Rapid – same day results possible
Shelf life up to 1-2 years without refrigeration
Limited/no instrumentation; can be performed at theperiphery of health systems without laboratory or electricity
Some tests as accurate as reference-level laboratory tests
Source: PATH RDT website: http://www.rapid-diagnostics.org
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
Disadvantages Disadvantages Cost per test more than traditional tests
Some have limited shelf lives therefore increased demandson procurement and distribution
Mainly produce only "yes/no" answers
Could require subjective interpretation (reader variation)
Rapid tests can be less sensitive or less accuratecompared to existing tests
Source http://www.rapid-diagnostics.org
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
RDT use in algorithmsRDT use in algorithms
Algorithms are decision trees or visual schemes
Include behavioural, biological, or genetic risk factors for adisease, clinical signs and symptoms, use of other tests
Consider disease incidence and prevalence, availabilityand accuracy of other tests, probable consequences ofmisdiagnosis
Algorithms may be population specific and need to beupdated periodically
Source: http://www.rapid-diagnostics.org
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
AlgorithmsAlgorithms
Source WHO Rapid HIV tests: guidelines for use in HIV testing and counselling services in resource-constrained settings, 2004
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
Necessity of AlgorithmsNecessity of Algorithms« The selection of the rapid HIV tests and test algorithms … is a responsibility of national governments … should not be delegated, either expressly or by neglect, to commercial enterprises, donor agencies or external aid programmes. The decision on which tests to use should be made following country-level technical assessments and the evaluation of other relevant factors, such as cost, current and continued availability, shelf-life and storage requirements. In each country these assessments … should preferably be the responsibility …of referral laboratories. Before selecting rapid test kits, many countries evaluate tests by using local specimens to confirm sensitivity and specifi city in their particular settings »
Source WHO Rapid HIV tests: guidelines for use in HIV testing and counselling services in resource-constrained settings, 2004
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
CostCost
Cost analysis : cost of using this diagnostic test oralgorithm in terms of personnel, facilities, equipment,sample collection materials, reagents, etc.
Cost-benefit analysis : cost of a correct diagnosis minusthe benefits from reaching that correct diagnosis
• Averted treatment costs and losses due to illness (e.g. wages)
• Less tangible costs e.g. reduced pain and suffering to patients
• Very difficult to cost benefits accurately and there is much debate on the accuracy of cost-benefit analyses.
Source: http://www.rapid-diagnostics.org
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
CostCost
Cost-effectiveness analysis : costs of a diagnostictest or algorithm compared to the health outcomeresulting from the diagnosis
Answers the following:
Relative to other tests or algorithms, is this test oralgorithm a good use of health care funds?
Source: http://www.rapid-diagnostics.org
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
Cost: malaria example Cost: malaria example
Source: http://www.wpro.who.int/rdt
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
AccuracyAccuracy
Source WHO Rapid HIV tests: guidelines for use in HIV testing and counselling services in resource-constrained settings, 2004
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
AccuracyAccuracyPositive and negative predictive values* for various HIV prevalences
HIV prevalence 0.1% 1% 5% 10% 30%
NPV with one non-reactive test
100%
100% 99.9%
99.9%
99.9%
PPV with one reactive test 9% 50% 83.9%
91.7%
98.5%
PPV with two reactive tests 90.8%
99.0%
99% 99.9%
100%
*A sensitivity of 99% and a specificity of 99% have been used in these calculations. Predictive values have been rounded to one decimal place
NPV= negative predictive valuePPV= positive predictive value
Source WHO Rapid HIV tests: guidelines for use in HIV testing and counselling services in resource-constrained settings, 2004
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
Barriers to use of RDTBarriers to use of RDTAcceptability
• To policymakers, clinicians, and patients
• Sufficient sensitivity and specificity for the approval of international health and donor agencies
• Adequate predictive value and ease-of-use for clinicians, require culturally appropriate specimens
• Perceived as credible, to be accepted by patients
• Users must trust and accept RDT results, if tests are perceived as too simple, results may not be trusted
Source: http://www.rapid-diagnostics.org
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
Barriers to use of RDTBarriers to use of RDT
Affordability
• Many RDTs are more expensive than other tests or algorithms they are intended to replace
– Especially true if RDT is used as a replacement for a syndromic algorithm
• Affordability constraints can be reduced by
– Working to decrease the cost per test
– Carefully designing algorithms to use the tests cost-effectively
– Educating users of cost-savings for more efficient use of therapeutic drugs
Source: http://www.rapid-diagnostics.org
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
Barriers to use of RDTBarriers to use of RDTAvailability
• RDT not consistently available in many developing countries
• Most tests have a limited shelf life and many countries have poorly developed procurement and distribution systems
• The consistency and quality of imported tests
– Local government regulations, quality assurance, shelf life testing, and distribution systems all need to be assessed and improved
Source: http://www.rapid-diagnostics.org
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
Role of laboratoriesRole of laboratories
Central public health laboratories
• Developing algorithms
• Writing standard operating procedure (SOP)
• National External Quality Control Scheme organization
• RDT accuracy testing – a certification process
• Training courses at peripheral level
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
Role of laboratoriesRole of laboratoriesPeripheral laboratories need
• Well trained people
• SOP and quality assurance culture
• Basic laboratory equipment (refrigerator, pipettes and tips, water bath)
• Sample collection and transportation experience
• Data collection and registration experience
Try to involve lab specialist as much as possible
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
ConclusionConclusion
RDT should be used in outbreak detection and investigation
Several manufactures
Be aware of the limitations and constraints
Use algorithms
Involve laboratories at central and peripheral level
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
Additional resourcesAdditional resources
Medecins Sans Fontieres (video on meningitis RDT)
Malaria RDT http://www.wpro.who.int/rdt/
• guidelines, reviews, trials etc.
http://www.rapid-diagnostics.org/
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
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
Investigation strategies and methods
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