Tuberculosis control strategies to reach the 2035 global targets in China
Background: Significant progress in tuberculosis (TB) control has been achieved worldwide over the last two decades. Global TB mortality has fallen by 45%, and TB incidence is declining. Recently, the World Health Organization (WHO) established an ambitious post-2015 global strategy, the End TB Strategy. This strategy outlines a 2025 milestone of 50% reduction in incidence and 75% reduction in mortality, and an overall 2035 target of 90% reduction in incidence and 95% reduction in mortality. In order to reach these targets, countries will likely need to redouble their TB control efforts and perhaps adopt new TB control strategies.
Between 1992 and 2012, China made impressive progress in TB control. Prior to 1992, most TB patients were treated in private hospitals, where patients typically received low-quality care - improper treatment was widespread, and only approximately 20% of patients had supervised TB treatment. In addition, nearly 50% experienced interrupted or shortened treatment and there was little follow-up of patients who dropped out or relapsed after a treatment episode. Starting in 1992, China ramped up a high-quality directly observed treatment, short-course (DOTS)-based strategy in Center for Disease Control (CDC) public health clinics in 13 provinces covering half the population, requiring hospitals to refer suspected TB patients to the CDC system. In the early 2000s, the DOTS program was expanded nationwide and an Internet-based disease reporting system was introduced -, further increasing referrals from the hospital to the CDC system. By 2010 it was estimated that approximately 80% of all TB patients were confirmed and treated within the CDC system ,, where the treatment success rate was estimated to be 85%.
Methods: The present study utilizes the Disease Transmission Kernel (DTK) model developed by the Institute for Disease Modeling group at Intellectual Ventures. The model and all necessary input files are available by request at the Institute for Disease Modeling website. Additional file 1 details the model structure, assumptions, and a complete list of model inputs. The model schematic is included in Figure 1.
Model and treatment schematic. A. Model schematic. Individuals are born healthy and may subsequently acquire latent TB infections through transmission. Disease progresses through latent disease, binned into latent fast or latent slow, through an active presymptomatic phase, and to active symptomatic disease. Individuals in the active presymptomatic and active symptomatic phases are infectious (excluding those with extrapulmonary TB). At the start of active disease, individuals may seek treatment. Individuals may die from non-disease mortality at any phase, but disease mortality only occurs in the active symptomatic phase. B. Treatment pathways. Individuals seek treatment either in the CDC or in private hospitals. Once on treatment, they can either be cured, relapse, fail, or die during treatment. Individuals who fail treatment in hospitals can seek retreatment in the CDC or again seek treatment in hospitals. See Additional file 1 for additional details on how the disease progression and treatment pathways were handled in the model.
Conclusions: The combination of an aging demographic in China and the increasing role of reactivation disease represents a growing challenge to TB control as China considers its post-2015 strategy. We have constructed a mathematical model of TB transmission at the country level in China, taking into account aging of the population and estimating the contribution of reactivation to overall incidence. The nationwide roll-out of the DOTS program reduced the annual risk of infection(ARI) , by improving treatment outcomes and reducing infectiousness from treatment experienced individuals. Given the high population coverage of DOTS in the CDC public health clinics, we estimate that new transmission is not the major driver of overall TB incidence. Rather, reactivation disease, combined with the growing elderly population, will be the major determinant of the decline in TB incidence and mortality over the next two decades.