Transcript Oral Presentation 1

Enhancing the rational use
of antimalarials: The costeffectiveness of rapid
immunochromatographic
dipsticks in sub-Saharan
Africa
Malaria Diagnosis
 Current practice – presumptive
treatment (WHO,1999)
 ACTs are expensive
 Misdiagnosis
 Rapid dipstick tests are being
developed for simple diagnosis
WHO (1996) IMCI Information Package
Study Questions
 At what levels of malaria prevalence is
dipstick diagnosis cost-effective?
 How much should we be willing to pay
for further information about model
parameters before making a decision?
Simple decision tree model
Suspected malaria
Malaria
True Positive
False Negative
Sensitivity
No Malaria
True Negative
False Positive
Specificity
PT: 100%
0%
0%
100%
Dip: 86-94%
6-14%
72-99%
1-28%
Probabilistic sensitivity analysis
 Uncertainty around most parameters
represented by lognormal and beta
distributions
 Incremental cost-effectiveness ratios
(ICERs) calculated probabilistically using
Monte-Carlo simulation
 ICERs converted to net-benefit
Net Benefit = Effects * λ – Costs
 The ceiling ratio (λ) is US $150 per DALY
averted (WHO, 1996)
WHO (1996) Report of the Ad Hoc Committee on Health
Research Relating to Future Investment Options
Probability Cost-Effective
Probability cost-effective
Ceiling Ratio = $150/DALY averted
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
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0%
20%
40%
60%
Malaria Prevalence
80%
100%
$40
$20
-$40
-$60
-$80
Malaria Prevalence
10
0%
80
%
70
%
60
%
50
%
40
%
30
%
20
%
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10
%
-$20
90
%
$0
0%
Incremental Net Benefit
Incremental Net-benefit
Calculation of EVPI
Ceiling Ratio = $150/DALY averted
Iterations
Net Benefit
Dipsticks
Net Benefit
PT
Net Benefit
WPI
1
$40
$20
$40
2
$20
$25
$25
3
$35
$25
$35
4
$25
$30
$30
Average
$30
$25
$32.50
EVPI =
$32.50 - $30 = $2.50
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
$2.50
$2.00
EVPI per person
Probability costeffective
EVPI according to prevalence
Probability
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or chart can go.
cost-
$1.00
$0.50
0%
$0.00
20% 40% 60% 80% 100%
Malaria Prevalence
effective
EVPI per
per person
Discussion
 Cost-effectiveness most sensitive to
 Epidemiological setting
 Cost and accuracy of dipsticks
 Probability patients return for treatment
 Further benefits
 Reduce drug pressure and development
of drug resistance
 Encourage use of treatment facilities
 Epidemiological surveillance
Limitations of the model
 Assumes that health workers and
patients trust and follow dipstick
results
 False positive diagnoses are not well
defined
 Does not consider private sector
 Not applicable in areas where
microscopy is currently in use
 EVPI depends on number of variables
you include in your model
Further work
• Conduct a EVSI analysis to determine
which parameters warrant further testing
 Consider parasite density, immunity, and
health worker behaviour
• Determine affordability of dipsticks at a
national level
 Predict impact on drug resistance
Acknowledgements




Chris Whitty
Sarah Staedke
Shunmay Yeung
Andrew Briggs
Funders: UK Department for
International Development, LSHTM
Health Economics and Financing
Programme