Individual-Level Modifiers of the Effects of Particulate Matter on Daily Mortality

Abstract

Consistent evidence has shown a positive association between particulate matter with an aerodiameter of less than or equal to 10 μm (PM₁₀) and daily mortality. Less is known about the modification of this association by factors measured at the individual level. The authors examined this question in a case-crossover study of 20 US cities. Mortality events (1.9 million) were obtained for nonaccidental, respiratory, heart disease, and stroke mortality between 1989 and 2000. PM₁₀ concentrations were obtained from the US Environmental Protection Agency. The authors examined the modification of the PM₁₀–mortality association by sociodemographics, location of death, season, and secondary diagnoses. They found different patterns of PM₁₀–mortality associations by gender and age but no differences by race. The level of education was inversely related to the risk of mortality associated with PM₁₀. PM₁₀-related, out-of-hospital deaths were more likely than were in-hospital deaths, as were those occurring during spring/fall versus summer/winter. A secondary diagnosis of diabetes modified the effect of PM₁₀ for respiratory and stroke mortality. Pneumonia was a positive effect modifier for deaths from all causes and stroke, while secondary stroke modified the effects for all-cause and respiratory deaths. The findings suggest that more attention must be paid to population characteristics to identify greater likelihood of exposures and susceptibility and, as a result, to improve policy making for air pollution standards.

air pollution, effect modifiers (epidemiology), mortality

CI, confidence interval, PM₁₀, particulate matter with an aerodiameter of less than or equal to 10 μm