Particulate Matter and Daily Mortality: A Case-Crossover Analysis of Individual Effect Modifiers.

BACKGROUND:: Several time-series studies have established the relationship between particulate matter (PM10) and mortality. We adopted a case-crossover design to evaluate whether individual socio-demographic characteristics and chronic or acute medical conditions modify the PM10-mortality association. METHODS:: We selected all natural deaths (321,024 subjects) occurring among adult (aged 35+ years) residents of 9 Italian cities between 1997 and 2004. We had access to individual information on socio-demographic variables, location of death, and chronic conditions (hospital admissions in the preceding 2-year period). For in-hospital deaths, we collected information on treatment wards at time of death and acute medical conditions. In a case-crossover analysis we adjusted for time, population changes, and meteorological conditions. RESULTS:: PM10 was associated with mortality among subjects age 65 years and older (0.75% increase per 10 mug/m [95% confidence interval = 0.42% to 1.09%]), with a more pronounced effect among people age 85 and older. A weaker effect was found among the most affluent people. The effect was present for both out-of-hospital and in-hospital deaths, especially among those treated in general medicine