Can greenspace modify the combined effects of multiple air pollutants on pulmonary tuberculosis treatment outcomes? An empirical study conducted in Zhejiang Province, China

Abstract

Background: Evidence on the combined effects of air pollutants and greenspace exposure on pulmonary tuberculosis (PTB) treatment is limited, particularly in developing countries with high levels of air pollution.

Objective: We aimed to examine the individual and combined effects of long-term exposure to air pollutants on PTB treatment outcomes while also investigating the potential modifying effect of greenspace.

Methods: This population-based study included 82,784 PTB cases notified in Zhejiang Province, China, from 2015 to 2019. The 24-month average concentrations of particulate matter with an aerodynamic diameter ≤2.5 µm (PM_2.5), ozone (O₃), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) before PTB diagnosis were estimated using a dataset derived from satellite-based machine learning models and monitoring stations. Greenspace exposure was assessed using the annual China Land Cover Dataset. We conducted analyses using time-varying Cox proportional hazards models and cumulative risk indices.

Results: In individual effect models, each 10 µg/m³ increase in PM_2.5, NO₂, O₃, and SO₂ concentrations was associated with hazard ratios for PTB treatment success of 0.95 (95% confidence interval (CI): 0.93–0.97), 0.92 (95% CI: 0.91–0.94), 0.98 (95% CI: 0.97–0.99), and 1.52 (95% CI: 1.49–1.56), respectively. In combined effect models, long-term exposure to the combination of air pollutants was negatively associated with PTB treatment success, with a joint hazard ratio (JHR) of 0.79 (95% CI: 0.63–0.96). Among the pollutants examined, O₃ contributed the most to the increased risks, followed by PM_2.5 and NO₂. Additionally, areas with moderate levels of greenspace showed a reduced risk (JHR = 0.81, 95% CI: 0.62–0.98) compared with the estimate from the third quantile model (JHR = 0.68, 95% CI: 0.52–0.83).

Conclusions: Combined air pollutants significantly impede successful PTB treatment outcomes, with O₃ and PM_2.5 accounting for nearly 75% of this detrimental effect. Moderate levels of greenspace can mitigate the adverse effects associated with combined air pollutants, leading to improved treatment success for patients with PTB.