Air pollution and daily mortality: A new approach to an old problem

Many time-series studies find associations between acute health effects and ambient air quality under current conditions. However, few such studies link mortality with morbidity to provide rational bases for improving public health. This paper describes a research project that developed and validated a new modeling approach directly addressing changes in life expectancies and the prematurity of deaths associated with transient changes in air quality. We used state-space modeling and Kalman filtering of elderly Philadelphia mortality counts from 1974-88 to estimate the size of the population at highest risk of imminent death. This subpopulation appears stable over time but is sensitive to season and to environmental factors: ambient temperature, ozone, and total suspended particulate matter (TSP), as an index of airborne particles in this demonstration of methodology. This population at extreme risk averages fewer than 0.1% of the elderly. By considering successively longer lags or moving averages of TSP, we find that cumulative short-term effects on entry to the at-risk pool tend to level off and decrease as periods of exposure longer than a few days are considered. These estimated environmental effects on the elderly are consistent with previous analyses using conventional time-series methods. However, this new model suggests that such environmentally linked deaths comprise only about half of the subjects whose frailty is associated with environmental factors. The average life expectancy of persons in the at-risk pool is estimated to be 5-7 days, which may be reduced by less than one day by environmental effects. These results suggest that exposures leading up to severe acute frailty and subsequent risk of imminent death may be more important from a public health perspective than those directly associated with subsequent mortality. (C) 2012 Elsevier Ltd. All rights reserved.