The influence of lower respiratory illness on childhood asthma: defining risk and susceptibility.

This article reviews the role of lower respiratory illness as a risk factor for the development of asthma in childhood. Lower respiratory illness may influence the natural course of lung-function growth and decline directly or indirectly promoting the development of asthma symptoms in susceptible individuals. The authors discuss the current definitions of lower respiratory illness and asthma and the characteristics of the individuals most prone to their effects. Last, they review how socioeconomic status and race affect the lower respiratory illness-asthma relationship.