Viral infections and obstructive airway disease in early life

Viral infections of the respiratory tract are a major cause of episodes of wheezing, perhaps being the most common cause of acute wheezing illnesses in infancy and early childhood. As many as 40 per cent of acute wheezing episodes in young children are associated with recovery of viral pathogens in throat cultures, despite inherent difficulties in recovering many of these agents. It has been estimated that, in the first year of life, 11 cases of respiratory infection associated with wheezing will occur for each 100 children observed for this period. In the second year of life, six cases can be expected per 100 children followed, while the rate remains above 1 per 100 throughout elementary school ages. This article will review the vast fund of knowledge recently accumulated concerning the relationship of viral infections to obstructive airway disease and will attempt to answer certain questions that are of great importance to the clinician as well as the academician. These questions include: Which infectious? Are asthmatic individuals more susceptible to viral infection than are nonasthmatics? Do viral infections (by inducing alterations in the immune status of the host) 'sensitize' the individual and thereby precipitate a long-term allergic diathesis? What are the mechanisms by which viral infections results in wheezing? Do viral infections of the lower respiratory tract in early life result in long-term abnormalities in lung development?