The role of respiratory virus infections in childhood asthma inception.

Viral respiratory illnesses associated with wheezing are extremely common during early life and remain a frequent cause of morbidity and hospitalization in young children. Although many children who wheeze with respiratory viruses during infancy outgrow the problem, most children with asthma and reductions in lung function at school age begin wheezing during the first several years of life. Whether symptomatic viral infections of the lower respiratory tract are causal in asthma development or simply identify predisposed children remains a controversial issue. Wheezing illnesses caused by respiratory syncytial virus (RSV), particularly those severe enough to lead to hospitalization, have historically been associated with an increased risk of asthma at school age. However, with the development of molecular diagnostics, human rhinovirus (HRV) wheezing illnesses have been recognized more recently as a stronger predictor of school-age asthma than RSV. In this article, the authors review the impact of virus infections during early life, focusing primarily on RSV and HRV, and their potential roles in asthma inception.