Air pollution and the duration of acute respiratory symptoms

The possibility that air pollution exposure can extend the duration of respiratory symptoms was examined in a diary study of student nurses. This diary study has already shown associations between air pollution and incidence rates of respiratory symptoms. After individual risk factors and temperature were controlled for, photochemical oxidants were significantly (p less than .0001) associated with the duration of episodes of coughing, phlegm, and sore throat. Some heterogeneity of response to oxidants was seen; there was little effect on asthmatics, but the impact increased as family income increased. Plots of the mean duration of symptoms, by quintiles of oxidants, for which the other covariates were controlled, showed strong signs of a dose-response relationship for coughing and phlegm and moderate signs of a monotonic dose-response relationship for sore throat. The relationships continued for concentrations below the current ambient standard for ozone. Chest tightness or discomfort was significantly associated with sulfur dioxide (p = .016), but the effect seemed mainly restricted to asthmatics. However, evidence for a dose-dependent increase was weak.