Effects of smoking and solid-fuel use on COPD, lung cancer, and tuberculosis in China: a time-based, multiple risk factor, modelling study

Abstract

Background: Chronic obstructive pulmonary disease (COPD), lung cancer, and tuberculosis are three leading causes of death in China, where prevalences of smoking and solid-fuel use are also high. We aimed to predict the effects of risk-factor trends on COPD, lung cancer, and tuberculosis.

Methods: We used representative data sources to estimate past trends in smoking and household solid-fuel use and to construct a range of future scenarios. We obtained the aetiological effects of risk factors on diseases from meta-analyses of epidemiological studies and from large studies in China. We modelled future COPD and lung cancer mortality and tuberculosis incidence, taking into account the accumulation of hazardous effects of risk factors on COPD and lung cancer over time, and dependency of the risk of tuberculosis infection on the prevalence of disease. We quantified the sensitivity of our results to methods and data choices.

Findings: If smoking and solid-fuel use remain at current levels between 2003 and 2033, 65 million deaths from COPD and 18 million deaths from lung cancer are predicted in China; 82% of COPD deaths and 75% of lung cancer deaths will be attributable to the combined effects of smoking and solid-fuel use. Complete gradual cessation of smoking and solid-fuel use by 2033 could avoid 26 million deaths from COPD and 6.3 million deaths from lung cancer; interventions of intermediate magnitude would reduce deaths by 6-31% (COPD) and 8-26% (lung cancer). Complete cessation of smoking and solid-fuel use by 2033 would reduce the projected annual tuberculosis incidence in 2033 by 14-52% if 80% DOTS coverage is sustained, 27-62% if 50% coverage is sustained, or 33-71% if 20% coverage is sustained.

Interpretation: Reducing smoking and solid-fuel use can substantially lower predictions of COPD and lung cancer burden and would contribute to effective tuberculosis control in China.

Figure 1

Compartmental susceptible–latent–infectious–recovered (SLIR) model of tuberculosis infection When susceptible (S) individuals are infected, they enter a state of fast latency (L) from which they may experience primary progression to the infectious (I) state. If not progressed within 5 years of infection, patients enter slow latency, where they may progress to the infectious state via endogenous reactivation at a greatly reduced rate. Individuals in the infectious state can be treated and enter the recovered (R) state from which they remain at risk of relapse to active disease. Individuals in the slowly progressive latent state or the recovered state are at risk of reinfection, although prior infection confers partial immunity. Individuals in any state can die, and new individuals enter the system via the susceptible compartment.

Figure 2

Annual mortality in men from COPD (A) and lung cancer (B) and in women from COPD (C) and lung cancer (D) under combined scenarios of smoking and solid fuel use Not avoidable deaths are those if risk-factor exposures were reduced to zero in 2003. See webfigures 4 and 5 for separate results for smoking and solid fuel use.

Figure 3

Sum of annual deaths 2003–33 for both sexes if exposure for both sexes to smoking and solid fuel use are reduced to zero by 2033

Figure 4

Annual incidence of infectious tuberculosis under combined effects of smoking and indoor air pollution scenarios by municipality and DOTS effectiveness Decreases in incidence with optimum, moderate, or minimum DOTS in Jiangsu (A, B, C, respectively) and Guizhou (D, E, F) and for Shanghai (G), which already has effective DOTS so non-optimum scenarios not shown.