Sensitivity Analysis Relative to the Baseline Model
| Scenario Name | Parameter to Change | Default Value | Effect of Variation on Model Output |
|---|---|---|---|
| 1. Current notifications | Estimated TB burden | 90% | If estimated TB burden is reduced to show only the capacity needed for current TB notifications, this will reduce the number of modules needed by a total of 32% (range: 8%–55%). |
| 2. Reduced TB prevalence | Number of adults with symptoms needed to test with rapid diagnostic (Xpert) to diagnose 1 adult TB patient (NNT) | 10 | Number of needed modules changes almost proportionately (e.g., increasing to 12 tests will increase output by up to 19%). As prevalence decreases, the value will increase. |
| 3. More screening of PLHIV | Percentage of PLHIV on ART with signs and symptoms of TB that require Xpert test | 20% | Increasing the percentage to 30% will increase number of modules needed by a total of 6% (range: 0%–38%). |
| 4. Less screening of PLHIV | Decreasing to 10% will decrease number of modules needed by a total of 6% (range: 0%–38%). | ||
| 5. Current screening of PLHIV | Decreasing to 2.5% will decrease number of modules needed by an average of 10% (range: 0%–67%). | ||
| 6. Increased operation of module | Operational capacity | 168 days/year 3 cycles/day | Increasing working days to 240 and test throughput to 4 cycles/day will reduce number of modules needed by 48% in all countries. |
| 7. CXR triage | Number needed to test | 10 | Including CXR as a triage tool before the WRD is estimated to reduce the number needed to test to 5 for HIV-negative adults and 2 for children, and to reduce the baseline number of PLHIV on ART requiring Xpert testing by 50%; in total, this would therefore reduce the number of modules and cartridges needed by 50%. See text for justification. |
| 8. Ambitious case finding | Number needed to test and operational capacity | 10 for NNT; 3 cycles/day | To detect all people with TB, more ambitious case finding is needed. This is likely to result in both more down-time for modules (due to greater decentralization and/or using mobile screening, thus cycles/day is reduced to 2) and a lower positivity rate from testing more people with symptoms of TB (thus NNT is increased to 20). This combination of changes increases modules and cartridges needed by 177% and 84% (range: 80%–194% and 20%–96%). |
| 9. WRD sites | Access standard for smear microscopy | None | Converts access standard for smear microscopy (1 microscope/100,000 population) to WRD sites needed to achieve same geographical coverage. This produces a large number of sites needed, though these values are more than 4 times lower than the baseline modules needed, since each site will require multiple modules to achieve sufficient throughput. |
Abbreviations: CXR, chest X-ray; NNT, Number needed to test; PLHIV, people living with HIV; TB, tuberculosis; WRD, World Health Organization-recommended rapid diagnostic.