Differential effects of size-specific particulate matter on lower respiratory infections in children: A time-series analysis in Lanzhou, China

Abstract

This study aimed to assess the differential effects of size-specific PM (PM2.5, PM10–2.5, and PM10) on daily outpatients for Lower Respiratory Infection (LRI), Pneumonia, and Bronchitis among children in Lanzhou, China. A distributed lag nonlinear model (DLNM) was employed to evaluate the non-linear and delayed effects. The models were fitted with different lag structures, including single lag days from the current to the previous seven days (lag0 to lag7) and moving average concentrations over seven lag days (lag0–1 to lag0–7). We found that different PM fractions were significantly associated with hospital visits for LRI, pneumonia, and bronchitis, and cumulative effects increased with the increasing number of lag days investigated. Relative risk (RR) of LRI outpatient visits among children per 10 µg/m3 increase in PM2.5, PM10–2.5, and PM10 were 1.070 (95% CI: 1.059, 1.081), 1.010 (95% CI: 1.006, 1.015), and 1.013 (95% CI: 1.010, 1.016), respectively. For every 10 μg/m3 increase in PM2.5, PM10–2.5, and PM10, the RR values for pneumonia were 1.081, 1.013, and 1.019, and those for bronchitis were 1.069, 1.009, and 1.012, respectively. Boys and children aged 0–3 years were more sensitive to PM exposure. We also found significantly higher effects of PM in cold seasons than that in warm seasons. Our results suggested that short-term exposure to size-specific PM, PM2.5 in particular, might be an important trigger of outpatient visits for overall and cause-specific LRI.