Effects of fine particulate matter and its constituents on childhood pneumonia: a cross-sectional study in six Chinese cities

Abstract Background Evidence of the effects of fine particulate matter (PM2·5) and its chemical constituents on childhood pneumonia is scarce. We aimed to investigate the effects of PM2·5 and its chemical constituents on doctor-diagnosed pneumonia in preschool children in China. Methods A cross-sectional study was done in six Chinese cities (ie, Shanghai, Nanjing, Chongqing, Changsha, Urumqi, and Taiyuan), based on the China, Children, Homes and Health project (2011–12), and included 30 759 preschool children across 205 preschools. Information on the prevalence of life-ever pneumonia, demographic characteristics, and home environmental factors were collected by validated questionnaires. Questionnaires were answered by parents or guardians of the children, and completed questionnaires were returned within 1 week, under the guidance of trained project investigators. The annual levels of ambient air pollutants (PM2·5, ozone, and dust) and five major PM2·5 chemical constituents (ie, black carbon, organic carbon, and three water-soluble ions [ammonium, NH4+; sulphate, SO42−; and nitrite, NO3−]) were obtained from a combination of satellite remote sensing, chemical transport modelling, and ground-based monitors (spatial resolution of 0·01° × 0·01° [ie, 1 km × 1 km]). The ambient air pollutants and chemical constituents were allocated to children according to geocoded preschool addresses. A hierarchical multiple regression model was done to evaluate the associations between PM2·5 and chemical components and childhood pneumonia at the preschool level and at the individual level, after adjusting for covariates. The study was approved by the ethics committee of the School of Public Health, Fudan University, Shanghai, China. Findings The prevalence of life-ever doctor-diagnosed pneumonia was significantly different between the six cities (p=0·004). Apart from family history of allergy, parental smoking, indoor dampness, and interior decoration, we found the prevalence of diagnosed pneumonia was significantly associated with the ambient PM2·5 (per 10 μg/m3) by an adjusted odds ratio (OR) of 1·10 (95% CI 1·00–1·21). The secondary chemical components, NH4+, SO42−, and NO3− (per 1 μg/m3), were significantly associated with childhood pneumonia, as shown by adjusted ORs of 1·08 (1·02–1·14), 1·04 (1·00–1·08), and 1·05 (1·01–1·09), respectively. Stratified analyses showed children who lived in urban areas or who were breastfed for less than 6 months had increased risk of pneumonia by ambient NH4+, SO42−, or NO3− exposure. Interpretation The chemical constituents of PM2·5, especially the water-soluble parts of NH4+, SO42−, and NO3−, were significantly associated with childhood pneumonia in China. This association indicates that these constituents might be important environmental triggers of childhood pneumonia. Funding National Key R&D Program of China, National Natural Science Foundation of China, the State Key Basic Research Program (973) Project.