Short-term exposure to ambient particulate matter and hospital outpatient visits for respiratory diseases among children: A five-city time-series study in China

Abstract

Background: Evidence concerning the association between ambient particulate matter (PM) and outpatient visits for respiratory diseases is quite limited, especially in children at a multicity level. Methods: A time-series study was performed in five Chinese cities from 2013 to 2018 among children aged 0-14 years. The city-specific effects of PM were estimated for time lags of zero up to seven days using the overdispersed generalized additive models after adjusting for time trends, meteorological variables, day of the week and holidays. Meta-analyses using random effects models were applied to pool the effect estimates in the five cities. The exposure-response relationship curves were also evaluated. Results: Exposure to PM was dose-responsive related to an increased respiratory outpatient visits among children. The cumulative lag effects of PM showed higher estimates than that of single-day exposure, and the lag07 (moving averages for the present day and the previous 7 days) concentrations of fine particles (PM2.5) and inhalable particles (PM10) produced the largest estimates. Each 10 μg/m3 increment in PM2.5 and PM10 at the lag07 was associated with a 1.39% (95% CI: 0.36%, 2.43%) and 1.11% (95% CI: 0.38%, 1.84%) increase in outpatient visits for all respiratory diseases among children, respectively, and the associations remained statistically significant at levels below the current Chinese Ambient Air Quality Standards (CAAQS). The effect estimates for acute lower respiratory infections (ALRIs) tended to be higher. Children 7-14 years old and 4-6 years old are the most susceptible groups for acute upper respiratory infections (AURIs) and ALRIs, respectively, but no sex differences were observed. Moreover, the effects of PM were stronger in the transition season of Beijing and Xining, whereas stronger in the cold season of the other 3 cities. Conclusions: Ambient PM concentrations, even at levels below the CAAQS, was dose-responsive associated with increased respiratory outpatient visits among children.