Fine particulate matter constituents associated with emergency room visits for pediatric asthma: a time-stratified case–crossover study in an urban area

BACKGROUND: Global asthma-related mortality tallies at around 2.5 million annually. Although asthma may be triggered or exacerbated by particulate matter (PM) exposure, studies investigating the relationship of PM and its components with emergency department (ED) visits for pediatric asthma are limited. This study aimed to estimate the impact of short-term exposure to PM constituents on ED visits for pediatric asthma. METHODS: We retrospectively evaluated non-trauma patients aged younger than 17 years who visited the ED with a primary diagnosis of asthma. Further, measurements of PM with aerodynamic diameter of < 10 μm (PM(10)), PM with aerodynamic diameter of < 10 μm (PM(2.5)), and four PM(2.5) components (i.e., nitrate (NO(3−)), sulfate (SO(4)(2−)), organic carbon (OC), and elemental carbon (EC)) were collected between 2007 and 2010 from southern particulate matter supersites. These included one core station and two satellite stations in Kaohsiung City, Taiwan. A time-stratified case-crossover study was conducted to analyze the hazard effect of PM. RESULTS: Overall, 1597 patients were enrolled in our study. In the single-pollutant model, the estimated risk increase for pediatric asthma incidence on lag 3 were 14.7% [95% confidence interval (CI), 3.2–27.4%], 13.5% (95% CI, 3.3–24.6%), 14.8% (95% CI, 2.5–28.6%), and 19.8% (95% CI, 7.6–33.3%) per interquartile range increments in PM(2.5), PM(10), nitrate, and OC, respectively. In the two-pollutant models, OC remained significant after adjusting for PM(2.5), PM(10), and nitrate. During subgroup analysis, children were more vulnerable to PM(2.5) and OC during cold days (< 26 °C, interaction p = 0.008 and 0.012, respectively). CONCLUSIONS: Both PM(2.5) concentrations and its chemical constituents OC and nitrate are associated with ED visits for pediatric asthma. Among PM(2.5) constituents, OC was most closely related to ED visits for pediatric asthma, and children are more vulnerable to PM(2.5) and OC during cold days.