Three Exposure Metrics for Fine Particulate Matter Associated With Outpatient Visits for Acute Lower Respiratory Infection Among Children in Guangzhou, China.

Ambient fine particulate matter (PM) is associated with an elevated risk of acute lower respiratory infections (ALRI). However, this association has not been examined using alternative exposure metrics. We collected outpatient data of patients with ALRI aged <14 years from the administrative database of a large tertiary hospital in Guangzhou, China, from 2013 to 2019. Ambient PM was measured using three metrics: (a) daily mean, (b) daily excessive concentration hours (DECH), and (c) hourly peak. Generalized additive models were fitted to estimate the excess risk (ER) associated with PM. A total of 105,639 ALRI (35,310 pneumonia and 68,218 bronchiolitis) outpatient visits were identified during the study period. An interquartile range increment in PM DECH was consistently associated with the highest ER of ALRI-related outpatient visits: 12.30% (95% confidence interval [CI]: 9.49-15.18%), compared with 11.20% (95% CI: 8.34-14.13%) for daily mean and 9.73% (95% CI: 6.97-12.55%) for hourly peak. The associations between the three metrics of PM and ALRI-related outpatient visits were stronger in the cold season than in the warm season. Future studies should consider PM DECH as an alternative method of exposure measurement, in addition to daily mean and hourly peak concentrations of PM.