Emergency Department Visits in Children Associated with Exposure to Ambient PM1 within Several Hours

Abstract

Background: Emerging evidence has integrated short-term exposure to PM1 with children’s morbidity and mortality. Nevertheless, most available studies have been conducted on a daily scale, ignoring the exposure variations over the span of a day. Objective: The main intention of this study was to examine the association between pediatric emergency department visits (PEDVs) and intra-day exposures to PM1 and PM2.5. We also aimed to investigate whether a high PM1/PM2.5 ratio elevated the risk of PEDVs independent from PM2.5 exposure within several hours. Methods: We collected hourly data on aerial PM1 and PM2.5 concentrations, all-cause PEDVs, and meteorological factors from two megacities (i.e., Guangzhou and Shenzhen) in southern China during 2015–2016. Time-stratified case-crossover design and conditional logistic regression analysis were used to assess the associations of PEDVs with exposures to PM1 and PM2.5 at different lag hours. The contribution of PM1 to PM2.5-associated risk was quantified by introducing PM1/PM2.5 ratio as an additional exposure indicator in the analysis adjusting for PM2.5. Subgroup analyses were performed stratified by sex, age, and season. Results: During this study period, 97,508 and 101,639 children were included from Guangzhou and Shenzhen, respectively. PM1 and PM2.5 exposures within several hours were both remarkably related to an increased risk of PEDVs. Risks for PEDVs increased by 3.9% (95% confidence interval [CI]: 2.7–5.0%) in Guangzhou and 3.2% (95% CI: 1.9–4.4%) in Shenzhen for each interquartile range (Guangzhou: 21.4 μg/m3, Shenzhen: 15.9 μg/m3) increase in PM1 at lag 0–3 h, respectively. A high PM1/PM2.5 ratio was substantially correlated with increased PEDVs, with an excess risk of 2.6% (95% CI: 1.2–4.0%) at lag 73–96 h in Guangzhou and 1.2% (95% CI: 0.4–2.0%) at lag 0–3 h in Shenzhen. Stratified analysis showed a clear seasonal pattern in PM-PEDVs relationships, with notably stronger risks in cold months (October to March of the following year) than in warm months (April to September). Conclusions: Exposures to ambient PM1 and PM2.5 within several hours were related to increased PEDVs. A high PM1/PM2.5 ratio may contribute an additional risk independent from the short-term impacts of PM2.5. These findings highlighted the significance of reducing PM1 in minimizing health risks due to PM2.5 exposure in children.