david dowdy, md phd june 6, 2013 ctr for tb research annual meeting
DESCRIPTION
A User-Friendly, Open-Source Tool to Project Impact and Costs of Diagnostic Tests for Tuberculosis . David Dowdy, MD PhD June 6, 2013 Ctr for TB Research Annual Meeting. David Dowdy, Jaso n Andrews, Pete Dodd, Robert Gilman. Background. - PowerPoint PPT PresentationTRANSCRIPT
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A User-Friendly, Open-Source Tool to Project Impact and Costs of Diagnostic
Tests for Tuberculosis
David Dowdy, MD PhDJune 6, 2013Ctr for TB ResearchAnnual Meeting
David Dowdy, Jason Andrews, Pete Dodd, Robert Gilman
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Background• Choosing between different TB diagnostic tests/algorithms is a
complex task.
• While we have data to inform this decision, those data are not synthesized in a readily-accessible fashion.
• Mathematical models have been constructed, but generally do not speak to actual decision-making.
– For example, “Implementation of Xpert would avert 132,000 TB cases in southern Africa over 10 years…at a cost of US$460 million”
– Nice if you’re the Minister of Health of “southern Africa”…
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Research Objective
To create a user-friendly modeling tool enabling decision-makers to compare TB diagnostic strategies as deployed within an epidemic representative of local
epidemiological and conditions
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Methods• Construct a steady-state TB epidemic using differential
equations– In areas of low incidence or emerging MDR, allow for non-equilibrium
dynamics to account for these trends• Create a program that will generate this steady-state for 3
variables:– TB incidence– MDR-TB prevalence– HIV prevalence
• Add in costs of diagnosis and treatment– As a simple function of “cost of first-line therapy”
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Underlying Model
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Diagnostic Options• Baseline: smear + existing array of tests• Culture if Previously Treated: baseline otherwise• Xpert for HIV-Positive Only: “best case” assuming perfect
knowledge of HIV status• Xpert if Smear-Positive: MDR-TB strategy (e.g., India)• Xpert for All: Treat RIF positive as MDR• Xpert for All, Culture Confirmation: Confirm RIF w/ culture• MODS/TLA for All: Slower but more sensitive than Xpert• Same-Day Microscopy: Eliminate “initial default,” 2x costs• Same-Day Xpert: Most expansive strategy
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User Interface
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modeling.modeltb.org
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Model Output: “High Incidence” Scenario
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Culture for Retreat
Xpert for All
MODS/TLA
Same-Day Smear(Cost-Saving)
Same-Day Xpert
Xpert, Smear+
Xpert, HIV+
Xpert, Culture Confirmed
0
50
100
150
200
250
0 50 100 150 200 250 300 350 400
Incr
emen
tal C
ost (
$, x1
,000
)
Incremental TB Cases Averted
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Comparing Settings
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-50
-25
0
25
50
75
100
2. Culture for Retreatment
3. Xpert for HIV-Positive
4. Xpert for Smear-Positive 5. Xpert for All
6. Xpert for All, Culture Confirmed 7. MODS/TLA
8. Same-day Microscopy
9. Same-day Xpert
% C
hang
e fr
om B
asel
ine
(Str
ateg
y 1) TB Incidence
MDR-TB
TB Mortality
Year 1 Cost
Cost After 5 Years
A. High Incidence Setting
-50
-25
0
25
50
75
100
2. Culture for Retreatment
3. Xpert for HIV-Positive
4. Xpert for Smear-Positive 5. Xpert for All
6. Xpert for All, Culture Confirmed 7. MODS/TLA
8. Same-day Microscopy
9. Same-day Xpert
% C
hang
e fr
om B
asel
ine
(Str
ateg
y 1) TB Incidence
MDR-TB
TB Mortality
Year 1 Cost
Cost After 5 Years
B. Low Incidence Setting
Delhi
Baltimore
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Open-Source Program Available
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Flexible Modeling Approach: Pros• Allows decision-makers to create models that are relevant to
their local situations– Only a handful of TB modelers in the world, thousands of settings– Where comparisons exist, this model seems to do well
• Provides insight by generating comparative scenarios– More useful to play and compare than come up with “one number”– For those with more modeling expertise, program is available
• Transparent conclusions– Very little “modeling mumbo-jumbo” behind the scenes– Simple model, simple results: can be understood!
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Flexible Modeling Approach: Cons• Arguably too simple
– Real-world complexities (e.g., level of ART availability) not included– Though code is available, few will change it
• Target audience difficult to define– MoH, etc., should be willing to hire technical advisors for this decision– Is this a flashy tool that nobody will end up using?
• Is open-source modeling dangerous?– Very few people understand the implications of model modifications– Models may be constructed that are grossly inappropriate
• We hope for “wikipedia-type” evolution…not guaranteed!12
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Summary• Global models are useful for publishing, but locally relevant
models are needed for actual decision-making.
• A flexible, Web-based, user-friendly model can provide users across the globe access to tailored modeling results.
– Free, open-source, modifiable platform– Web-based interface– Expanding to incorporate operational characteristics as well
• This strategy has great potential, but also important and controversial limitations.
– Our philosophy: “If we don’t try, we can’t even have the conversation.”
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Acknowledgments• Pete Dodd, LSHTM• Co-Authors
– Jason Andrews, MGH– Bob Gilman, JHSPH
• Flexible TB Modeling Team– Jonathan Golub, JHU– Dick Chaisson, JHU– Madhu Pai, McGill– Adithya Cattamanchi, UCSF
• Funding– NIH, R21AI101152
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