Increased Chronic Obstructive Pulmonary Disease Exacerbations of Likely Viral Etiology Follow Elevated Ambient Nitrogen Oxides

Epidemiologic research strongly supports an association between air pollution and chronic obstructive pulmonary disease exacerbations. Numerous mechanisms may underlie any association because pollutants are toxic to pulmonary cells and may increase susceptibility to respiratory infections. The relationship between ambient pollution and exacerbation etiology has not been studied. To evaluate the characteristics of pollution-associated exacerbations and whether the association is specific to exacerbations of infective or noninfective etiology. We analyzed the effect of preceding ambient particulate matter less than or equal to 10 μm in aerodynamic diameter, oxides of nitrogen (NOx), and ozone on characterized chronic obstructive pulmonary disease exacerbations in a regression model adjusted for temperature, seasonality, and long-term trend. We specifically examined associations with exacerbations of suspected viral and/or bacterial, or noninfective etiology. For the associations identified we further examined the characteristics of pollution-associated exacerbations. A total of 4,173 exacerbations occurred over the 20-year study period. Higher ambient NOx was consistently associated with increased viral-type exacerbations at 2-4 days lag (P = 0.010). Recovery for viral-type exacerbations after higher ambient NOx was significantly prolonged. These findings were consistent in the subset of 2,841 exacerbations treated with oral corticosteroids or antibiotics, with recovery 1.29 (95% confidence interval, 1.17-1.42; P