Effects of ambient air pollution on nonelderly asthma hospital admissions in Seattle, Washington, 1987-1994

As part of the Clean Air Act, Congress has directed EPA to set air quality standards to protect sensitive population groups from air pollutants in the ambient environment. People with asthma represent one such group. We under took a study of the relation between measured ambient air pollutants in Sea ttle and nonelderly hospital admissions with a principal diagnosis of asthm a. We regressed daily hospital admissions to local hospitals for area resid ents from 1987 through 1994 on particulate matter less than 10 and 2.5 mu m in aerodynamic diameter (PM10 and PM2.5, respectively); coarse particulate mass; sulfur dioxide (SO2); ozone (O-3); and carbon monoxide (CO) in a Poi sson regression model with control for time trends, seasonal variations, an d temperature-related weather effects. With the exception of seasonally mon itored O-3, we supplemented incomplete pollutant measures in a multiple imp utation model to create a complete time series of exposure measures. We fou nd an estimated 4-5% increase in the rate of asthma hospital admissions ass ociated with an interquartile range change in PM (19 mu g/m(3) PM10,11.8 mu g/m(3) PM2.5, and 9.3 mu g/m(3) coarse particulate mass) lagged I day; rel ative rates were as follows: for PM10 1.05 [95% confidence interval (CI) = 1.02-1.08]; for PM2.5, 1.04 (95% CI = 1.02-1.07); and for coarse particulat e mass, 1.04 (95% CI = 1.01-1.07). In single-pollutant models we also found that a 6% increase in the rate of admission was associated with an interqu artile range change in CO (interquartile range, 924 parts per billion; 95% CI = 1.03-1.09) at a lag of 3 days and an interquartile range change in O-3 (interquartile range, 20 parts per billion; 95% CI = 1.02-1.11) at a lag o f 2 days. We did not observe an association for SO2. We found PM and CO to be jointly associated with asthma admissions. We estimated the highest incr ease in risk in the spring and fall seasons.