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Background: Prospective cohort studies constitute the major source of evidence about the mortality effects of chronic exposure to particulate air pollution. Additional studies are needed to provide evidence on the health effects of chronic exposure to particulate matter < or = 2.5 microm in aerodynamic diameter (PM(2.5)) because few studies have been carried out and the cohorts have not been representative., Objectives: This study was designed to estimate the relative risk of death associated with long-term exposure to PM(2.5) by region and age groups in a U.S. population of elderly, for the period 2000-2005., Methods: By linking PM(2.5) monitoring data to the Medicare billing claims by ZIP code of residence of the enrollees, we have developed a new retrospective cohort study, the Medicare Cohort Air Pollution Study. The study population comprises 13.2 million participants living in 4,568 ZIP codes having centroids within 6 miles of a PM(2.5) monitor. We estimated relative risks adjusted by socioeconomic status and smoking by fitting log-linear regression models., Results: In the eastern and central regions, a 10-microg/m(3) increase in 6-year average of PM(2.5) is associated with 6.8% [95% confidence interval (CI), 4.9-8.7%] and 13.2% (95% CI, 9.5-16.9) increases in mortality, respectively. We found no evidence of an association in the western region or for persons > or = 85 years of age., Conclusions: We established a cohort of Medicare participants for investigating air pollution and mortality on longer-term time frames. Chronic exposure to PM(2.5) was associated with mortality in the eastern and central regions, but not in the western United States.

In this paper, we present national maps of relative rates of mortality associated with short-term exposure to particulate matter < 10 micro m in aerodynamic diameter (PM(10)). We report results for 88 of the largest metropolitan areas in the United States from 1987 to 1994 for all-cause mortality, combined cardiovascular and respiratory deaths, and other causes of mortality. Maximum likelihood estimates of the relative rate of mortality associated with PM(10)and the degree of statistical uncertainty were obtained for each of the 88 cities by fitting a separate log-linear regression of the daily mortality rate on air pollution level and potential confounders. We obtained Bayesian estimates of the relative rates by fitting a hierarchical model that takes into account spatial correlation among the true city-specific relative rates. We found that daily variations of PM(10) are positively associated with daily variations of mortality. In particular, the relative rate estimates of cardiovascular and respiratory mortality associated with PM(10) are larger on average than the relative rate estimates of all-cause and other-cause mortality. The estimated increase in the relative rate of death from cardiovascular and respiratory mortality, all-cause mortality, and other-cause mortality were 0.31% (95% posterior interval, 0.15-0.5), 0.22% (95% posterior interval, 0.1-0.38), and 0.13% (95% posterior interval, -0.05 to 0.29), respectively. Bayesian estimates of the city-specific relative rates ranged from 0.23% to 0.35% for cardiovascular and respiratory mortality, from 0.18% to 0.27% for all causes, and from 0.10% to 0.20% for other causes of mortality. The spatial characterization of effects across cities offers the potential to identify factors that could influence the effect of PM(10) on health, including particle characteristics, offering insights into mechanisms by which PM(10) causes adverse health effects.