Abstract

Many epidemiological studies provide evidence of an association between daily counts of mortality and ambient particulate matter less than 10 microns in diameter (PM10). Relatively few studies, however, have investigated the relationship of mortality with fine particles (PM2.5), especially in a multi-city setting. We examined associations between PM2.5 and daily mortality in nine heavily populated California counties using data from 1999 through 2002. We considered daily counts of all-cause mortality and several cause-specific subcategories (respiratory, cardiovascular, ischemic heart disease and diabetes). We also examined these associations among several subpopulations, including the elderly (age > 65), males, females, non-high school graduates, whites, and Hispanics. Poisson multiple regression models incorporating natural or penalized splines were used to control for covariates that could affect daily counts of mortality, including time, seasonality, temperature, humidity and day of the week. Meta-analyses using random effects were used to pool the observations in all nine counties. The analysis revealed associations of PM2.5 levels with several mortality categories. Specifically, a 10 µg/m3 change in two-day average PM2.5 concentration corresponded to a 0.6% (95% CI = 0.2 – 1.0) increase in all-cause mortality, with similar or greater effect estimates for several other subpopulations and mortality subcategories, including respiratory disease, cardiovascular disease, diabetes, those above age 65, females, deaths out of the hospital, and non-high school graduates. Results were generally insensitive to model specification and the type of spline model used. This analysis adds to the growing body of evidence linking fine particles with daily mortality.

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