Air pollution and pediatric respiratory disease: croup.

The question of a causative interrelation between air pollution and croup has received considerable attention by the mass media. A series of epidemiological studies has tried to establish a scientific basis for these speculations. Some studies have compared the occurrence of croup with locally measured concentrations of pollutants, while others have observed differences in the incidence of croup between populations subjected to different levels of pollution. Results have so far remained contradictory, most studies have failed to control for other variables, and thus clear-cut evidence for the etiologic role of air pollution has yet not been established on an epidemiological basis. On the other hand, simple croup is caused by viral infection, while recurrent croup is associated with allergy and airway hyperreactivity. Animal studies have documented that air pollution can reduce resistance against viral infections, increase the risk of allergic sensibilization, and induce airway hyperreactivity. Conceivably, air pollution could thus have a supportive role in the development of croup, but this possibility requires further investigation.