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

## TL;DR

This study explores how air pollution and greenspace affect the treatment outcomes of pulmonary tuberculosis in China, finding that pollution worsens outcomes but greenspace can help.

## Contribution

The study is the first to investigate how greenspace modifies the combined effects of multiple air pollutants on pulmonary tuberculosis treatment outcomes in a high-pollution region.

## Key findings

- Long-term exposure to combined air pollutants significantly reduces the success of pulmonary tuberculosis treatment.
- Moderate levels of greenspace exposure are associated with improved treatment success for pulmonary tuberculosis.
- Ozone and PM2.5 contribute most to the negative effects of air pollution on treatment outcomes.

## Abstract

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.

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.

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 (PM2.5), 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.

In individual effect models, each 10 µg/m3 increase in PM2.5, 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 PM2.5 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).

Combined air pollutants significantly impede successful PTB treatment outcomes, with O3 and PM2.5 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.

The online version contains supplementary material available at https://doi.org/10.1265/ehpm.24-00381.