Association of Low-Level Ozone and Fine Particles With Respiratory Symptoms in Children With Asthma

TLDR

Ozone and PM2.5 exposure above EPA standards is a known risk factor for respiratory symptoms in children with asthma. The study examined whether ozone and PM2.5 levels below EPA standards simultaneously affect daily respiratory symptoms and rescue medication use in asthmatic children. Ambient ozone (1‑hour and 8‑hour peaks) and 24‑hour PM2.5 concentrations were measured from April to September 2001, and logistic regression with generalized estimating equations was used to evaluate associations separately for maintenance‑medication users and nonusers. Among maintenance‑medication users, a 50‑ppb increase in 1‑hour ozone raised wheeze risk by 35 % and chest tightness by 47 %, while no significant associations were found in nonusers, indicating that maintenance‑medication‑using asthmatic children are especially vulnerable to ozone below EPA limits.

Abstract

Exposure to ozone and particulate matter of 2.5 microm or less (PM2.5) in air at levels above current US Environmental Protection Agency (EPA) standards is a risk factor for respiratory symptoms in children with asthma.To examine simultaneous effects of ozone and PM2.5 at levels below EPA standards on daily respiratory symptoms and rescue medication use among children with asthma.Daily respiratory symptoms and medication use were examined prospectively for 271 children younger than 12 years with physician-diagnosed, active asthma residing in southern New England. Exposure to ambient concentrations of ozone and PM2.5 from April 1 through September 30, 2001, was assessed using ozone (peak 1-hour and 8-hour) and 24-hour PM2.5. Logistic regression analyses using generalized estimating equations were performed separately for maintenance medication users (n = 130) and nonusers (n = 141). Associations between pollutants (adjusted for temperature, controlling for same- and previous-day levels) and respiratory symptoms and use of rescue medication were evaluated.Respiratory symptoms and rescue medication use recorded on calendars by subjects' mothers.Mean (SD) levels were 59 (19) ppb (1-hour average) and 51 (16) ppb (8-hour average) for ozone and 13 (8) microg/m3 for PM2.5. In copollutant models, ozone level but not PM2.5 was significantly associated with respiratory symptoms and rescue medication use among children using maintenance medication; a 50-ppb increase in 1-hour ozone was associated with increased likelihood of wheeze (by 35%) and chest tightness (by 47%). The highest levels of ozone (1-hour or 8-hour averages) were associated with increased shortness of breath and rescue medication use. No significant, exposure-dependent associations were observed for any outcome by any pollutant among children who did not use maintenance medication.Asthmatic children using maintenance medication are particularly vulnerable to ozone, controlling for exposure to fine particles, at levels below EPA standards.