The relationship between respiratory illness in childhood and chronic air-flow obstruction in adulthood.

This review evaluates the hypothesis that lower respiratory infection in childhood is a risk factor for chronic air-flow obstruction (CAO) in adulthood. Clinical CAO appears to result from a lengthy and initially asymptomatic loss of function that correlates with the development of peripheral airways abnormalities and emphysema. The relative functional silence of the small airways, the apparent vulnerability of the child's lung to injury, and the demonstration of functional abnormalities after several types of viral respiratory infection are consistent with the proposed role of lower respiratory infection. Relevant epidemiologic studies, however, have provided conflicting results, and many are flawed by recall bias. The observed association in children between lower respiratory infection and impaired ventilatory function may be noncausal and not a direct consequence of infection. A complete test of the hypothesis would require follow-up of study subjects from birth to adulthood with monitoring of respiratory infections and pulmonary function.