The epidemiological impact, costs, and cost-effectiveness of implementing household contact investigation with tuberculosis preventive treatment in Nepal: a model-based analysis

BACKGROUND: The burden of tuberculosis (TB) remains extremely high globally. It is increasingly recognized that contact investigation and preventive treatment are essential components of effective action to reduce TB. High-quality, local evidence of feasibility and impact is urgently needed to catalyse scale-up of preventive treatment in high-burden, resource-constrained settings. METHODS: We collected data on the costs and yields of contact investigation and implementation of three months of isoniazid and rifapentine (3HP) to treat latent TB infection (LTBI), among adult household members of people diagnosed with TB, from a pilot conducted in two districts of Nepal (Chitwan and Pyuthan) from August 2022 to March 2023. We developed and calibrated mathematical models representing each district and estimated the number of TB episodes and deaths averted by the intervention during 2023-2042. By combining net discounted costs and discounted impact, we estimated the incremental cost-effectiveness of the intervention (compared to no intervention) from a health system perspective as costs (United States Dollars (USD) in 2022) per disability-adjusted life-year (DALY) averted. RESULTS: The intervention screened 1,711 adult household contact persons for TB and LTBI, and treated 500 individuals for LTBI, achieving 98% 3HP acceptance and 95% completion at 150 USD per contact person treated (including drug and test procurement and implementation costs). Including the impact of treating TB disease, the intervention was projected to avert 141 (95% Uncertainty Interval (UI): 86-224) disease episodes and 24 (95% UI: 13-39) deaths during 2023-2042, or 8.2 episodes and 1.4 deaths averted per 100 contact persons screened. The incremental cost-effectiveness of the intervention was 119 USD (95% UI: 51-255) and 163 USD (95% UI: 76-328) per DALY averted in Chitwan and Pyuthan, respectively. CONCLUSIONS: Screening and treating household members of people with TB for both TB and LTBI can be successfully implemented in both rural and urban settings, is highly cost-effective and should be prioritized to reduce the TB burden in Nepal and similar high-burden countries.