Observed causative impact of fine particulate matter on acute upper respiratory disease: a comparative study in two typical cities in China.

Association between fine particulate matter (PM) and respiratory health has attracted great concern in China. Substantial epidemiological evidences confirm the correlational relationship between PM and respiratory disease in many Chinese cities. However, the causative impact of PM on respiratory disease remains uncertain and comparative analysis is limited. This study aims to explore and compare the correlational relationship as well as the causal connection between PM and upper respiratory tract infection (URTI) in two typical cities (Beijing, Shenzhen) with rather different ambient air environment conditions. The distributed lag nonlinear model (DLNM) was used to detect the correlational relationship between PM and URTI by revealing the lag effect pattern of PM on URTI. The convergent cross mapping (CCM) method was applied to explore the causal connection between PM and URTI. The results from DLNM indicate that an increase of 10 μg/m in PM concentration is associated with an increase of 1.86% (95% confidence interval: 0.74%-2.99%) in URTI at a lag of 13 days in Beijing, compared with 2.68% (95% confidence interval: 0.99-4.39%) at a lag of 1 day in Shenzhen. The causality detection with CCM quantitatively demonstrates the significant causative influence of PM on URTI in both two cities. Findings from the two methods consistently show that people living in low-concentration areas (Shenzhen) are less tolerant to PM exposure than those in high-concentration areas (Beijing). In general, our study highlights the adverse health effects of PM pollution on the general public in cities with various PM levels and emphasizes the needs for the government to provide appropriate solutions to control PM pollution, even in cities with low PM concentration.