Gent JF, Triche EW, Holford TR, et al. JAMA. 2003;290:1859–1867
Purpose of the Study.
Exposure to ozone and particulate matter of ≤2.5 μm (PM2.5) in air at levels above current US Environmental Protection Agency (EPA) standards is a risk factor for respiratory symptoms among children with asthma. This study sought to examine the 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, <12 years of age, with physician-diagnosed, active asthma who were residing in southern New England.
Exposure to ambient concentrations of ozone and PM2.5 from April 1, 2001, through September 30, 2001, was assessed with peak 1-hour and 8-hour ozone levels and 24-hour PM2.5 levels. Logistic regression analyses with generalized estimating equations were performed separately for maintenance medication users (n = 130) and nonusers (n = 141). Associations between pollutant levels (adjusted for temperature and controlling for same- and previous-day levels) and respiratory symptoms and rescue medication use were evaluated. Major outcome measures were respiratory symptoms and rescue medication use, as recorded on calendars by the subjects’ mothers.
Mean ± SD levels were 59 ± 19 ppb (1-hour average) and 51 ± 16 ppb (8-hour average) for ozone and 13 ± 8 μg/m3 for PM2.5. In copollutant models, ozone but not PM2.5 levels were significantly associated with respiratory symptoms and rescue medication use among children using maintenance medication; a 50-ppb increase in 1-hour ozone levels was associated with increased likelihoods 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 with any pollutant among children who did not use maintenance medication.
Asthmatic children using maintenance medication were particularly vulnerable to ozone, controlling for exposure to fine particles, at levels below EPA standards.
This is an excellent study that provides persuasive evidence regarding the adverse effects of air pollution in childhood asthma, even at levels that are generally regarded as safe.