Air pollution and mortality in a cohort of patients with chronic obstructive pulmonary disease: a time series analysis.

Many studies have shown an association between current daily levels of air pollution and daily mortality by respiratory and cardiovascular causes in the general population. However, the weak associations observed and the ecological nature of the exposure to air pollutants have created some doubts about plausibility of a causal relation. Specificity, which increases the plausibility of causal inference although its lack does not negate it, could be increased using a population more susceptible a priori. Hence, we assessed the association between daily levels of air pollutants and daily mortality in a cohort of chronic obstructive pulmonary disease (COPD) patients in Barcelona for the years 1985 to 1989. We hypothesised that patients with COPD are more likely to die after increased exposure to urban air pollution than the general population.