The effect of outdoor air pollution on mortality risk: an ecological study from Santiago, Chile

The aim of this ecological study was to investigate the effect of outdoor air pollution on the mortality risk of metropolitan inhabitants in Santiago de Chile. Cause-specific deaths by the day for the years 1988-1991 in Santiago de Chile were extracted from mortality data tapes of the National Center for Statistics. Deaths from accidents were excluded. Total and some specific respiratory diseases deaths were compared calculating the risk of death by municipality and month of the year using age-adjusted standardized mortality ratios (SMRs) controlling for socioeconomic level. Daily counts of deaths were regressed using a Poisson model on the total and fine suspended particles, SO2, CO and ozone on the preceding day, controlling for temperature and humidity. A clear pattern in the geographical distribution of risk of death, both for general mortality and specific respiratory causes (pneumonia, COPD and asthma) was found using SMR, with higher values in the most polluted areas regardless of socioeconomic and living conditions. A highly significant positive association was found between total mortality and both fine suspended particles and CO level. The association remained significant for those days with fine suspended particles levels below 150 micrograms/dl suggesting a no-threshold effect for the total number of deaths. These results are in agreement with previously reported associations, and they add to the body of evidence showing that particulate pollution is associated with increases daily mortality.