Does Temperature Modify the Association between Air Pollution and Mortality? A Multicity Case-Crossover Analysis in Italy

摘要

Adverse health effects of particulate matter 10 μm in aerodynamic diameter (PM₁₀) and high temperatures are well known, but the extent of their interaction on mortality is less clear. This paper describes effect modification of temperature in the PM₁₀–mortality association and tests the hypothesis that higher PM₁₀ effects in summer are due to enhanced exposure to particles. All deaths of residents of nine Italian cities between 1997 and 2004 were selected. The case-crossover approach was adopted to estimate the effect of PM₁₀ on mortality by season and temperature level. Three strata of temperature corresponding to low, medium, and high “ventilation” were identified, and the interaction between PM₁₀ and temperature within each stratum was examined. Season and temperature levels strongly modified the PM₁₀–mortality association: for a 10-μg/m3 variation in PM₁₀, a 2.54% increase in risk of death in summer (95% confidence interval: 1.31, 3.78) compared with 0.20% (95% confidence interval: −0.08, 0.49) in winter. Analysis of the interaction between PM₁₀ and temperature within temperature strata resulted in positive but, in most cases, nonstatistically significant coefficients. The authors found much higher PM₁₀ effects on mortality during warmer days. The hypothesis that such an effect is attributable to enhanced exposure to particles in summer could not be rejected.