Cost-effectiveness of Quantiferon®-TB Gold-in-Tube versus tuberculin skin testing for contact screening and treatment of latent tuberculosis infection in Brazil

Abstract

Background: Latent tuberculosis infection (LTBI) is a reservoir for new TB cases. Isoniazid preventive therapy (IPT) reduces the risk of active TB by as much as 90%, but LTBI screening has limitations. Unlike tuberculin skin testing (TST), interferon-gamma release assays are not affected by BCG vaccination, and have been reported to be cost-effective in low-burden countries. The goal of this study was to perform a cost-effectiveness analysis from the health system perspective, comparing three strategies for LTBI diagnosis in TB contacts: tuberculin skin testing (TST), QuantiFERON®-TB Gold-in-Tube (QFT-GIT) and TST confirmed by QFT-GIT if positive (TST/QFT-GIT) in Brazil, a middle-income, high-burden country with universal BCG coverage.

Methodology/principal findings: Costs for LTBI diagnosis and treatment of a hypothetical cohort of 1,000 adult immunocompetent close contacts were considered. The effectiveness measure employed was the number of averted TB cases in two years. Health system costs were US$ 105,096 for TST, US$ 121,054 for QFT-GIT and US$ 101,948 for TST/QFT-GIT; these strategies averted 6.56, 6.63 and 4.59 TB cases, respectively. The most cost-effective strategy was TST (US$ 16,021/averted case). The incremental cost-effectiveness ratio was US$ 227,977/averted TB case for QFT-GIT. TST/QFT-GIT was dominated.

Conclusions: Unlike previous studies, TST was the most cost-effective strategy for averting new TB cases in the short term. QFT-GIT would be more cost-effective if its costs could be reduced to US$ 26.95, considering a TST specificity of 59% and US$ 18 considering a more realistic TST specificity of 80%. Nevertheless, with TST, 207.4 additional people per 1,000 will be prescribed IPT compared with QFT.

Figure 1. Decision subtree diagram of the Tuberculin Skin Testing screening strategy for LTBI immunocompetent adult contacts.

Figure 2. Two-way sensitivity analysis of QFT-GIT costs at different TST specificities.

The red-shaded area represents the values where the QFT-GIT only strategy is more costly. The blue-shaded area represents the values where the TST only strategy is more costly. QFT strategy became less costly than TST if its costs were US$ 26.95 considering a TST specificity of 59% and US$ 18 considering a more realistic specificity of 80%.

Figure 3. Tornado diagram for Tuberculin Skin Testing versus QuantiFERON® Gold-In-Tube as the screening strategy for LTBI.

Termini of bars represent the incremental cost-effectiveness ratio (incremental cost/averted TB case) at the low and high assumption values for the different variables. Longer bars represent parameters to which the model is more sensitive.