Chronic and Acute Exposure to Ambient Fine Particulate Matter and Other Air Pollutants: National Cohort Studies of Mortality and Morbidity

TS3-04 Abstract: This research addresses a key uncertainty in the evidence on the effects of particulate matter (PM) on public health: the effects of longer-term exposure to airborne PM, including PM2.5, on morbidity and mortality. By using large, existing cohorts, established by federal agencies, specifically enrollees in Medicare, we have tested the hypothesis that long-term exposure to PM increases morbidity. Because the Medicare cohort includes daily data, we have also applied methods for time-series analysis to compare the effect of PM on time scales ranging from daily to yearly. The analysis uses the longitudinal data in the National Claims History File (NCHF). We have carried out this study for the years 1999 through 2002 by matching the participants in the NCHF using zip code of residence to the nearest air pollution monitors for PM2.5 and other pollutants, weather station, and zip code-level sociodemographic indicators. In an initial analysis, we have estimated the age–gender standardized mortality rates within the 250 largest counties where 11 million Medicare residents live. During the period of follow up, we observe more than 2 million deaths on approximately 50 million years of person-time. We have used log-linear regression to estimate that the rate of death is 6% (95% confidence interval [CI]: 4 to 8) higher in a county with 10 μg/m3 greater PM2.5 level. However, this difference in relative risk is reduced to 3% (−1 to 8) when potential spatial confounders are taken into account. When the counties are stratified into the eastern region or the west coast, we see little evidence of a PM2.5 effect in the west. Using the same data, we have also carried out daily time-series analyses. We considered daily counts of countywide hospital admissions for primary diagnosis of cerebrovascular, peripheral, and ischemic heart diseases, heart rhythm, heart failure, chronic obstructive pulmonary disease, respiratory infection, and injuries as a control outcome. We found evidence of short-term increased hospital admission rates associated with PM2.5 for all of the health outcomes except injuries. The largest effect was for heart failure: a 1.2% increase in risk per 10-μg/m3 increase in same-day PM2.5 (95% CI: 0.78 to 1.78%). We also found that cardiovascular risks tend to be higher in eastern counties. We document complementary short-term and long-term consequences of PM on Medicare participants and show the potential of the Medicare data for addressing air pollution and health at the national level.