Association between PM2.5 and all-cause and specific-cause mortality in 27 US communities

Abstract

While fine mode particulate matter (PM_2.5) forms the basis for regulating particles in the US and other countries, there is a serious paucity of large population-based studies of its acute effect on mortality. To address this issue, we examined the association between PM_2.5 and both all-cause and specific-cause mortality using over 1.3 million deaths in 27 US communities between 1997 and 2002. A two-stage approach was used. First, the association between PM_2.5 and mortality in each community was quantified using a case-crossover design. Second, meta-analysis was used to estimate a summary effect over all 27 communities. Effect modification of age and gender was examined using interaction terms in the case-crossover model, while effect modification of community-specific characteristics including geographic location, annual PM_2.5 concentration above 15 g/m³ and central air conditioning prevalence was examined using meta-regression. We observed a 1.21% (95% CI 0.29, 2.14%) increase in all-cause mortality, a 1.78% (95% CI 0.20, 3.36%) increase in respiratory related mortality and a 1.03% (95% CI 0.02, 2.04%) increase in stroke related mortality with a 10 g/m³ increase in previous day's PM_2.5. The magnitude of these associations is more than triple that recently reported for PM₁₀, suggesting that combustion and traffic related particles are more toxic than larger sized particles. Effect modification occurred in all-cause and specific-cause deaths with greater effects in subjects 75 years of age. There was suggestive evidence that women may be more susceptible to PM_2.5 effects than men, and that effects were larger in the East than in the West. Increased prevalence of central air conditioning was associated with a decreased effect of PM_2.5. Our findings describe the magnitude of the effect on all-cause and specific-cause mortality, the modifiers of this association, and suggest that PM_2.5 may pose a public health risk even at or below current ambient levels.