Meta-analysis of the Italian studies of short-term effects of air pollution (MISA), 1990-1999.

A meta-analysis of short-term effects of air pollution on health in eight Italian cities from 1990 to 1999 is presented. Death certificates and hospital admission data as well as daily concentrations of pollutants were collected. The same generalized linear model adjusted for age, day of the week, holidays, influenza epidemics, meteorological variables, and seasonality pattern was fitted to the city data. City-specific model selection was not done. In the meta-analysis, for each outcome, the city-specific estimates for each pollutant were combined using fixed and random-effects models. Hierarchical Bayesian models were use to investigate the effects of PM10 in detail. Each pollutant (SO2, NO2, CO, PM10, O3) was significantly associated with mortality for natural causes. The effect of PM10 on mortality was greater during the warm season and for elderly. A north-south gradient in risk was observed for total natural mortality. The excess risks on hospital admission were modified by deprivation score and by the NO2/PM10 ratio. Results add evidence for an association between air pollution and early mortality or morbidity and support the hypothesis of a synergism between meteorological variables and air pollution.