Contribution of respiratory disease to nonrespiratory mortality associations with air pollution.

Many time series studies have found that individuals with primary cardiac conditions were susceptible to the adverse effects associated with increased ambient particle levels. However, the mechanism(s) of these associations is not yet understood. In this study, we evaluate whether individuals with nonrespiratory primary causes of death who also had contributing respiratory causes listed on their death certificates were more affected by air pollution, as compared with those not having contributing respiratory conditions. Short-term associations between ambient particulate matter (10 microm or less in aerodynamic diameter) and mortality were modeled in New York City for the years 1985-1994. It was observed that among those 75 years or more, those with contributing respiratory disease had higher relative risks (95% confidence intervals) calculated per interquartile range, as compared with those without contributing respiratory disease for both circulatory deaths (relative risk = 1.066 [1.027-1.106] versus 1.022 [1.008-1.035]) and cancer deaths (relative risk = 1.129 [1.041-1.225] versus 1.025 [1.000-1.050]). However, this pattern of association was not observed for those who were less than 75 years old. The results of this study suggest that past studies may have underestimated the role of respiratory disease in pollution-mortality associations, especially among older adults.