Mortality in the Medicare Population and Chronic Exposure to Fine Particulate Air Pollution in Urban Centers (2000-2005)
Zeger, Scott L., Dominici, Francesca, McDermott, Aidan, Samet, Jonathan M., Environmental Health Perspectives
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 [less than or equal to ] 2.5 [mu]m in aerodynamic diameter ([PM.sub.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 longterm exposure to [PM.sub.2.5] by region and age groups in a U.S. population of elderly, for the period 2000-2005.
METHODS: By linking [PM.sub.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.sub.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-[mu]g/[m.sup.3] increase in 6-year average of [PM.sub.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 cvidence of an association in the western region or for persons [greater than or equal to] 85 years or age.
CONCLUSIONS: We established a cohort of Medicare participants for investigating air pollution and mortality on longer-term time frames. Chronic exposure to [PM.sub.2.5] was associated with mortality in the eastern and central regions, but not in the western United States.
KEY WORDS: ecologic bias, fine particulate matter ([PM.sub.2.5]), heterogeneity, log-linear models, Medicare, mortality, prospective studies. Environ Health Perspect 116:1614-1619 (2008). doi: 10.1289/ehp.11449 available via http://dx.doi.org/[Online 12 August 2008]
Particulate matter (PM) air pollution is a global public health problem (Cohen et al. 2004). In developing countries, levels of airborne PM still reach concentrations at which serious health consequences are well documented (Chhabra et al. 2001; Ostro et al. 1999a, 1999b; Vichit-Vadakan et al. 2001). In developed countries, recent epidemiologic studies show evidence of continued adverse effects, even though PM levels have declined in the last two decades (Dominici et al. 2006; Jerrett et al. 2005; Laden et al. 2006; Pope et al. 2002). Increased mortality associated with higher levels of PM air pollution has been of particular concern, giving an imperative for stronger protective regulations (Bachmann 2007; Samet et al. 2006).
The evidence on PM and health shows acute and chronic effects (Pope and Dockery 2006). The London Fog of 1952 provides dramatic evidence of the risk of extremely high levels of PM air pollution over a period of about a week (Bell and Davis 2001; Bell et al. 2004; Logan 19853). Multisite time-series studies estimate associations between the risk of death and the level of air pollution shortly before death (shorter-term effects). These studies have provided evidence that far lower levels of PM than those that occur during events like the London Fog are still associated with increased risk over several days (Dominici et al. 2006, 2007; Katsouyanni et al. 1997; Lee et al. 2000; Samoli et al. 2001). Cohort studies estimate associations between time to death and exposure to air pollution over multiple years (longer-term effects). The design of these studies involves follow-up of cohorts for mortality over periods of years to decades and an assessment of mortality risk in association with estimated longer-term exposure to air pollution (Dockery et al. 1993; Hoek et al. 2002; Jerrett et al. 2005; Krewski et al. 2004; Laden et al. 2006; Pope at al. …