Associations between ambient air pollution and mortality from all causes, pneumonia, and congenital heart diseases among children aged under 5 years in Beijing, China: A population-based time series study

Background: Previous studies have mainly focused on the associations between particulate matters and infant mortality. However, evidence regarding the associations between gaseous pollutants and mortality among children aged < 5 years remains sparse. Objectives: The aim of this study was to investigate the associations between ambient air pollution and death among children aged < 5 years in Beijing, China, and explore the impact of age, gender and specific causes of death on these associations. Methods: Concentrations of ambient air pollution and the number of deaths among children aged < 5 years in Beijing from January 2014 to September 2016 were extracted from authoritative electronic databases. The associations were estimated for a single-month lag from the current month up to the previous 5 months (lag0-lag5) and moving averages of the current and previous months (lag01-lag05) using generalized additive Poisson regression (adjusted for time trends, season, meteorological variables and holidays). Subgroup analyses related to age, gender and specific diseases were performed. Two-pollutant models were used to evaluate the possible role of single pollutants. Results: Sulfur dioxide (SO2), nitrogen dioxide (NO2) and carbon monoxide (CO) demonstrated the strongest associations with death among children aged < 5 years at lag0 and the estimates decreased or even turned negative with the increasing lag periods. For an interquartile range increase in SO2, NO2 and CO at lag0, the odds ratios (OR) were 1.332 (95% CI 1.152-1.539), 1.383 (95% CI 1.113-1.718) and 1.273 (95% CI 1.028-1.575). However, CO lost significance after adjusting for SO2 and NO2, and PM2.5 gained significance (OR 1.548, 95% CI 1.061-2.258) after adjusting for PM10. The ORs for SO2 and NO2 remained the most stable across all two-pollutant models. The associations for children aged 1-5 years were stronger than those reported for infants at lag but lower at the other lag months. The pollutant associations were stronger for congenital heart disease-related death than overall and pneumonia-related death. We did not find significant differences in terms of gender. Conclusion: Exposure to air pollution may increase the incidence of death among children aged < 5 years. SO2 and NO2 may be the most stable pollutants reflecting associations between air pollution and death, deserving further attention. Children with congenital heart diseases are more susceptible to air pollution. Therefore, it is urgent to implement the clean air targets established by WHO and reduce the exposure of children to air pollution.