AIR-POLLUTION AND EMERGENCY ROOM VISITS FOR ASTHMA IN SANTA-CLARA COUNTY, CALIFORNIA

During the winters of 1986-1987 through 1991-1992, rainfall throughout much of Northern California was subnormal, resulting in intermittent accumulation of air pollution, much of which was attributable to resid ential wood combustion (RWC). This investigation examined whether ther e was a relationship between ambient air pollution in Santa Clara Coun ty, California and emergency room visits for asthma during the winters of 1988-1989 through 1991-1992. Emergency room (ER) records from thre e acute-care hospitals were abstracted to compile daily visits for ast hma and a control diagnosis (gastroenteritis) for 3-month periods duri ng each winter. Air monitoring data included daily coefficient of haze (COH) and every-other-day particulate matter with aerodynamic diamete r equal to or less than 10 microns (PM10, 24-hr average), as well as h ourly nitrogen dioxide and ozone concentrations. Daily COH measurement s were used to predict values for missing days of PM10 to develop a co mplete PM10 time series. Daily data were also obtained for temperature , precipitation, and relative humidity. In time-series analyses using Poisson regression, consistent relationships were found between ER vis its for asthma and PM10. Same-day nitrogen dioxide concentrations were also associated with asthma ER visits, while ozone was not. Because t here was a significant interaction between PM10 and minimum temperatur e in this data set, estimates of relative risks (RRs) for PM10-associa ted asthma ER visits were temperature-dependent. A 60 mu g/m(3) change in PM10 (2-day lag) corresponded to RRs of 1.43 (95% CI = 1.18-1.69) at 20 degrees F, representing the low end of the temperature distribut ion, 1.27 (95% CI = 1.13-1.42) at 30 degrees F, and 1.11 (95% CI = 1.0 3-1.19) at 41 degrees F, the mean of the observed minimum temperatures . ER visits for gastroenteritis were not significantly associated with any pollutant variable. Several sensitivity analyses, including the u se of robust regressions and of nonparametric methods for fitting time trends and temperature effects in the data, supported these findings. These results demonstrate an association between ambient wintertime P M10 and exacerbations of asthma in an area where one of the principal sources of PM10 is RWC.