An association between PM2.5 and pediatric respiratory outpatient visits in four Chinese cities

Background: The effects of exposure to particulate matter with aerodynamic diameter less than 2.5 mu m (PM2.5) on children's respiratory system were investigated in numerous epidemiological literatures. However, studies on the association between PM2.5 and pediatric outpatient visits for respiratory diseases, especially considering the multicenter studies were limited in China. Objectives: To study the association between the short-term exposure to PM2.5 and the number of children's outpatient visits for respiratory diseases in four Chinese cities as well as the pooled health effects. Methods: Data of pediatric outpatient visits for respiratory diseases (RD, ICD: J00-J99) from representative hospitals in Shijiazhuang (SJZ), Xi' an (XA), Nanjing (NJ) and Guangzhou (GZ) in China from 2015 to 2018 were collected and the air quality data for the same period were collected from environmental protection departments. Generalized additive model (GAM) with quasi-Poisson regression was conducted to analyze the effects of PM2.5 on the number of pediatric outpatient visits in each city. Single-day lag model (lag0 to lag7) and moving average lag model (lag01 and lag07) were used to examine the lag effects and cumulative effects. Random-effects metaanalysis was used to pool the estimated risks of four cities. The interactions between PM2.5 and temperature were also explored. Results: The average daily/total outpatient visits for RD, in SJZ, XA, NJ and GZ from 2015 to 2018 were 854.2/1,245,384, 2353.9/3,439,025, 1267.2/1,851,438 and 1399.5/2,044,740 respectively. The percentages of acute upper respiratory infections (URD, ICD: J00-J06) and other acute lower respiratory infections (LRD, ICD: J20J22) in RD were 33%, 13% (SJZ), 43%, 32% (XA), 26%, 21% (NJ) and 54%, 26% (GZ). The largest pooled estimates of single-day lag effects for RD, URD, and LRD were at lag0, lag0 and lag1. Every 10 mu g/m(3) increase in PM2.5 concentration was associated with a 0.46% (95%CI: 0.21%-0.70%), 0.50% (95%CI: 0.19%-0.81%) and 0.42% (95%CI: 0.06%-0.79%) increased number of outpatient visits significantly. While max cumulative effects which were all at lag 07 were 1.10% (95%CI: 0.46%-1.74%), 0.96% (95%CI: 0.20%-1.73%) and 1.06% (95%CI: 0.12%-2.00%). Less polluted cities (GZ and NJ) showed greater city-specific excess risks, but the excess risks significantly decreased after adjusting for NO2 in two-pollutant models. Generally, PM2.5 showed larger health hazards on lower temperature days. Conclusions: Our study showed that exposure to the ambient PM2.5 was associated with the increase of the number of outpatient visits with pediatric respiratory diseases in four Chinese cities. The health effects of PM2.5 may not be independent of other air pollutants and could be modified by temperature.