Table 1.
Model parameters: base-case values, assumptions and ranges used in the sensitivity analyses
| Parameter | Base-case value | Range | References |
|---|---|---|---|
| Prevalence of latent tuberculosis infection (LTBI) at the time of hire (before baseline testing) | 10.0% | (10–30%) | [6] |
| Probability of being recently infected among those with LTBI at baseline | 16.7% | (10–30%) | Model assumption |
| Proportion of healthcare workers (HCWs) performing high-risk activities | 27.0% | (10–30%) | [16] |
| Annual risk of TB exposure in HCWs performing high-risk activities: | |||
| Base-case scenario | 4.4% | (0–40%) | [12, 17] |
| Alternate scenario assuming higher risks | 13.1% | (0–40%) | [17, 18] |
| Annual risk of TB exposure in HCWs performing intermediate-risk activities: | |||
| Base-case scenario | 1.3% | (0–15%) | [12, 17] |
| Alternate scenario assuming higher risks | 4.4% | (0–15%) | [17, 18] |
| Probability of acquiring new TB infection given exposure | 22.9% | (0–30%) | [18] |
| Adherence of HCWs to annual screening (mandatory for continued employment) | 100% | (50–100%) | Model assumption |
| Probability that TB exposure is recognised | 75.0% | (50–100%) | Model assumption |
| Probability of being screened after TB exposure is recognised (tuberculin skin test) | 88.8% | (50–100%) | [19] |
| Probability of being screened after TB exposure is recognised (QuantiFERON®-TB-Gold) | 95.0% | (50–100%) | [20] |
| Sensitivity of tuberculin skin test in serial testing | 95.0% | (70–100%) | [26, 29] |
| Sensitivity of QuantiFERON®-TB-Gold in serial testing | 95.0% | (70–100%) | [27, 28] |
| Specificity of tuberculin skin test for serial testing, after baseline negative test | 97.0% | (70–100%) | [23] |
| Specificity of QuantiFERON®-TB-Gold for serial testing after baseline negative test | 95.0% | (70–100%) | [6, 11] |
| Efficacy of isoniazid preventive treatment | 90.0% | (80–100%) | [42] |
| Probability that isoniazid is recommended to worker after conversion on repeat testing | 100% | (50–100%) | Model assumption |
| Probability that worker with conversion starts isoniazid treatment, after recommendation to take it | 82.9% | (50–100%) | [43] |
| Probability that isoniazid treatment is completed, once started | 47.3% | (40–100%) | [43] |
| Risk of mild isoniazid-induced hepatitis | 0.1% | [44] | |
| Risk of fatal isoniazid-induced hepatitis | 0.002% | [44] | |
| Annual risk of progression from LTBI to active TB for recently infected (≤2 years since onset of infection) | 2.5% | (0–2.5%) | [21] |
| Annual risk of progression from LTBI to active TB for remotely infected (>2 years since onset of infection) | 0.1% | [22] | |
| Risk of death from active TB | 4.6% | (0–10%) | [45] |
| Risk of major adverse event with treatment for active TB | 5.1% | [44] | |
| Risk of death, given major adverse event with treatment for active TB | 1.5% | [44] | |
| Costs (in 2015 CAN dollars; $1 CAN = $0.77 US) | |||
| Diagnosis for active TB disease | $354 | [46–48] | |
| Inpatient treatment of active TB disease | $13,063 | [49] | |
| Outpatient treatment of active TB disease | $3,748 | [50] | |
| Tuberculin skin test | $15 | ($10–30) | [51] |
| QuantiFERON®-TB-Gold | $50 | ($10–50) | [51] |
| Complete treatment for LTBI | $591 | [52] | |
| Incomplete treatment for LTBI | $272 | [52] | |
| Isoniazid-induced hepatitis (mild) | $400 | [53] | |
| Isoniazid-induced hepatitis (fatal) | $13,078 | [53] | |
| Quality of life adjustments: QALYs lost per year | |||
| Active TB disease treatment | 0.15 | (0.10–0.30) | [24, 25] |
| Latent TB treatment | 0.03 | (0–0.05) | [24, 25] |