Table 1.
Cohort model inputs including costs, effectiveness measures and tree probabilities
| Model Parameter Inputs | Parameter Value | Range (Min, Max) |
Data Source |
|---|---|---|---|
|
Cost Parameters | |||
| Cost of 1st Line TB Treatment | $185 | (154, 236) | 20,21 |
| Cost of 2nd Line TB Treatment | $1759 | (1353, 2351) | 20,21 |
| Lifetime cost of ART started immediately | $2563 | (0, 4000) | CHAI Treatment costs for HIV (MATCH study) 22 |
| Cost of a symptom screen | $0.20 | (0, 1) | Chepetsa costing study |
| Cost of standard smear (1000 tests/year at peripheral lab) | $4.06 | (1, 10) | Chepetsa costing study |
|
Effectiveness parameters | |||
|
(Including effectiveness of ART) | |||
| DALY – 1st line treatment success | −1.53 | (−2.53, −0.5) | 14,23 |
| DALY – 2nd line treatment success | −1.9878 | (−2.99, −0.99) | 14,23 |
| DALY – Death | −23.8967 | (−27.8967, −29.90) | 9,13,14 |
| DALY – No TB, ART initiation (delayed and immediate) | −1.2710 | (−2.2710, −0.27) | 9,13,14 |
|
Cohort proportions | |||
| Probability of active TB among patients newly diagnosed with HIV in Malawi | .024 | (0.01, 0.06) | Chepetsa, facility report |
| Probability that symptomatic patients would receive smear results without screening | .40 | (0,1) | |
| Probability that CD4+ <350 at time of screening | .60 | (0.5, 0.75) | 24 |
| Probability that missed TB case is later diagnosed with TB outside of screening | 0.66 | (0.61, 0.71) | 8 |
| Probability of loss to follow up during TB treatment | .15 | (0.1, 0.21) | 23 |
| Probability of Rifampicin resistance among patients with TB | .004 | (0.0014, 0.01) | 8 |
| Probability of death among TB patients with HIV given treatment failure, missed diagnosis, or loss to follow-up | 1 | (0.63, 1) | Assumption 25 |
| Probability of treatment success, MDR-TB treated with 1st line drugs | .47 | (0.42, 0.52) | 10 |
| Probability of Treatment success, smear-negative TB treated with 1st line therapy | .8 | (0.72, 0.88) | 8 |
| Probability of Treatment success, smear positive TB treated with 1st line therapy | .87 | (0.78, 0.96) | 8 |
| Probability of treatment success, 2nd line | .80 | (0.7, 0.9) | 11 |
|
Diagnostic Parameters | |||
| Sensitivity of Xpert for RIF resistance | .976 | (0.94, 0.99) | 26,27 |
| Sensitivity of Xpert for LED-negative TB | .718 | (0.29, 0.79) | 26–28 |
| Sensitivity of Xpert for LED-positive TB | .977 | (0.92, 0.99) | 26,27 |
| Sensitivity of LED for TB among Smear negatives | 0.095 | (0.09, 0.2) | 8,25,29 |
| Sensitivity of LED for TB among Smear positives | 1 | (0, 1) | 29 |
| Specificity of GXP | .992 | (0.98, 0.996) | 26,27 |
| Specificity of GXP for RIF resistance | 1 | (0.9, 1) | 26,27 |
| Specificity of LED | 0.944 | (0.92, 0.96) | 30 |
| Sensitivity of standard smear among LED positive people with HIV | .37 | (0.36, 0.7) | 8,25 |
| Specificity of smear among people with HIV | .8 | (0, 1) | |
Abbreviations: TB: active tuberculosis disease, GXP: Gene Xpert, LED: light emitting diode fluorescence microscopy, MDR: multi drug resistant tuberculosis, ART: antiretroviral therap