Coarse particles and mortality: evidence from a multi-city study in California

To examine the risk of all-cause and cardiovascular mortality associated with short-term coarse particle exposure in California while addressing issues of exposure misclassification by limiting the study to those residing near a pollution monitor.

Deaths in 15 California counties from 1999 to 2005 were linked to coarse particulate monitoring data. Case deaths were limited to those residing in a zip code within 20 km of a pollution monitor. We used conditional logistic regression with a case-crossover design to estimate county-specific effects of coarse particles. County estimates were then pooled using random-effects meta-analysis to create overall study estimates. Effects specific to race and educational status were also analysed.

We observed an increased excess risk (ER) of both all-cause mortality (ER per 10 microg/m(3) = 0.7%, 95% CI -0.1 to 1.5) and cardiovascular mortality (ER per 10 microg/m(3) = 1.3%, 95% CI 0.1 to 2.5) from a 2-day lag in coarse particles. Greater effects were observed among Hispanics and non-high school graduates. Adjustment for fine particles and decreasing the inclusion buffer to 10 km did not substantively alter the results.

Our study provides further evidence of an association between acute exposure to coarse particles and mortality, and supports the hypothesis that lower socioeconomic status groups may be more susceptible to its effects.