Table 1.
Key parameters for cost-effectiveness analysis
| Value | Base case | Low | High | Source |
|---|---|---|---|---|
| Epidemiologic, diagnostic, and treatment parameters | ||||
| Prevalence of LTBI | 0.21 | 0.0875 | 0.85 | 7,10 |
| Proportion of patients with CD4 ≤ 200 cells/μl | 0.10 | 0.001 | 0.775 | 7 |
| Proportion with LTBI progressing to active TB in patients with CD4 > 200 cells/μl (CD4 ≤ 200 cells/μl)* | 0.125 (0.218) | 0.0312 (0.0312) | 0.3 (0.75) | 10,13–16 |
| Relative risk reduction in progression to active TB with 6-month IPT† | 0.63 | 0.20 | 0.94 | 3,10,13,14,16,17 |
| IPT-induced hepatotoxicity in patients with CD4 > 200 cells/μl (patients with CD4 ≤ 200 cells/μl)‡ | 0.025 (0.05) | 0.00625 (0.0125) | 0.01 (0.15) | 13,18–20 |
| Probability of active TB case detection | 0.59 | 0.4 | 0.9 | 2 |
| Probability of cure of active TB with treatment in patients with CD4 > 200 cells/μl (CD4 ≤ 200 cells/μl) | 0.85 (0.76) | 0.212 (0.19) | 1 (1) | 2 |
| IPT and active TB treatment costs (2014 USD)¶ | ||||
| 6 months IPT | 22.77 | 5.69 | 90.00 | 21–23 |
| Mild IPT hepatotoxicity treatment | 35.73 | 8.93 | 62.53 | 21,22 |
| Severe hepatotoxicity treatment | 100.81 | 25.20 | 176.42 | 9,10 |
| Active TB diagnostics | 19.32 | 4.98 | 33.81 | 21,22,24 |
| Active TB treatment | 95.29 | 23.82 | 166.76 | 21–23 |
| Disability weights¶ | ||||
| Living with HIV on ART | 0.053 | 0.034 | 0.079 | 25 |
| Mild IPT-induced hepatotoxicity§ | 0.15 | 0.05 | 0.3 | 25–28 |
| Severe IPT-induced hepatitis§ | 0.6 | 0.1 | 0.9 | 25–28 |
| Active TB disease | 0.399 | 0.267 | 0.547 | 25,28 |
| Active TB treatment | 0.1 | 0.01 | 0.25 | 28 |
| Life expectancies, years¶# | ||||
| HIV on ART with CD4 > 200 cells/μl (CD4 ≤ 200 cells/μl) | 12.9 (6.45) | 3 (1.5) | 30 (15) | Assumption29 |
We modeled progression to active TB within 5 years of model entry. We also incorporated the possibility of tuberculous infection among TST-negative individuals either due to false-negative TST results or to infection after model entry (1% progression to active TB).
Assuming that the 6-month IPT completion percentage was 0.82 in the base case (range 0.205–1.0).10,30 For those who did not complete 6-month IPT, we estimated they received about 3 months of IPT, which resulted in a relative risk reduction of 0.315 in the base case (range 0.10–0.48).3,10,13,14,16,17
IPT-induced hepatotoxicity is defined as grade 3 or higher hepatitis: probability that once the patient has developed IPT-induced hepatitis that it will become ‘severe’. Severe hepatitis was defined as hepatitis grade 5 or higher or hepatitis involving hospitalization resulting in death. In the base case, we estimated that 56% of those with IPT-induced hepatotoxicity developed severe hepatitis (range 1.4–9.8) and 98% mortality due to severe hepatitis (range 24.5–100).19,20
Assuming that there was no disability associated with IPT alone, except through adverse events such as hepatitis or death.
Future costs and disability-adjusted life-years were discounted at 3%.11
Defined as the life expectancy with HIV at the median age of women in the model (assumed to be 25 years old, consistent with literature estimates) in India; we assumed that those who died due to severe hepatitis or active TB disease had a shortened life expectancy of 6 months (range 0.1–1.5 years).7
LTBI=latent tuberculous infection; TB=tuberculosis; IPT=isoniazid preventive therapy; USD=US dollar; HIV=human immunodeficiency virus; ART=antiretroviral therapy; TST = tuberculin skin test.