Three exposure metrics of size-specific particulate matter associated with acute lower respiratory infection hospitalization in children: A multi-city time-series analysis in China

The global burden of acute lower respiratory infection (ALRI) attributable to air pollution has increased in recent years, but the association between ALRI and exposure to size-specific particulate matter has not been investigated using different exposure metrics.We obtained ALRI admission from seven cities from 2014 to 2016 in China. Different sized particles were measured using three metrics (a) daily mean, (b) hourly peak, and (c) daily excessive concentration hours (DECH). Generalized additive models were fitted for each of the seven cities, and the city-specific estimates were then pooled using random-effects meta-analysis models. Stratified analyses were conducted to examine the effect modifications of gender, age, and season. We also estimated the disease burden due to particulate matter exposures.There were 111,426 ALRI (79,803 pneumonia and 31,622 bronchiolitis) hospital admissions under the age of 15 between 2014 and 2016 in our study. Daily means were associated with the largest ALRI estimates (95% confidence interval [CI]): 2.43% (0.79%, 4.11%) for PM2.5, 2.25% (0.11%, 4.44%) for PMc, and 2.64% (0.73%, 4.58%) for PM10. The magnitude of effect sizes were followed by DECH: 1.94% (0.51%, 3.39%) for PM2.5, 0.88% (-0.14%, 1.92%) for PMc, 1.86% (0.50%, 2.01%) for PM10; and hourly peak: 0.70% (-0.60%, 2.01%) for PM2.5, 1.05% (-0.13%, 2.66%) for PMc, and 1.20% (-0.20%, 2.62%) for PM10 at lag03. We found significantly higher effects in cold seasons than that in warm seasons, while we did not find a significant different between gender and age groups.The adverse effects of exposure to particulate matter on ALRI hospitalizations are reconfirmed. DECH was a possible alternative exposure indicator for PM2.5 assessment, which may affect air quality standards in the future.