Transmission dynamics and control of tuberculosis in high-altitude regions: a modelling study in Xizang, China

Objectives To estimate tuberculosis (TB) incidence trends in the high-altitude Xizang, China, and to explore the key intervention strategies on achieving the WHO 2030 TB control target. Design We developed a susceptible-exposed-infectious-recovered transmission model using routinely reported TB surveillance data from 2004 to 2022. Scenario-based simulations were conducted to project future TB incidence under alternative intervention strategies. Model assumptions are as follows: (1) a stable population, (2) lifelong vaccine-induced immunity, (3) infectiousness of active TB cases, (4) relapse risk after recovery and (5) homogeneous mixing within the population. Setting Seven prefectures of Xizang Autonomous Region on the Tibetan Plateau, China. Participants An estimated population of approximately 3 million individuals residing in Xizang. Interventions We assessed the epidemiological impact of four interventions implemented independently: increasing vaccine efficacy rate, reducing transmission rates of susceptible individuals, decreasing progression rate from latent TB infection to active disease and reducing relapse rate among successfully treated patients, compared with continuation of current control measures. Results The estimated basic reproduction number ( R 0 ) for TB in Xizang was 0.39 (95% CI 0.21 to 0.71) in the absence of additional interventions, which was the highest among all regions of China. Model simulations indicated that all four evaluated interventions were each likely to reduce TB incidence, but only reducing the latent-to-active TB progression had a substantial effect. A 50% reduction in the progression rate was predicted to lower TB incidence from 66.56 (62.00-70.11) to 40.54 (37.15-43.77) cases per 100 000 population, meeting the WHO 2030 TB control target. Conclusion Targeted management of individuals with latent TB infection should be strengthened to substantially reduce TB transmission in high-altitude areas.