Relationship between respiratory syncytial virus bronchiolitis and future obstructive airway diseases.

Evidence from a large number of prospective case-control studies shows that respiratory syncytial virus (RSV) bronchiolitis in infancy is often associated with recurrent wheezing and asthma during subsequent years. However, wheezing tends to diminish and most studies show no significant increase in wheezing compared to controls by school age or adolescence. An unresolved question is whether severe RSV infection during infancy causes the respiratory sequelae or inherent abnormalities predispose an infant to develop severe respiratory infection and sequelae, i.e. RSV is associated with the development of pulmonary sequelae. Studies on long-term outcome of RSV bronchiolitis are reviewed from an evidence-based perspective. The majority of prospective placebo-controlled studies do not show any long-term beneficial effects of corticosteroid treatment, i.e. the risk of subsequent wheezing is not diminished by the treatment. The evidence for an increased risk of allergic sensitization after RSV bronchiolitis is not nearly as strong as the evidence for an increased risk of subsequent wheezing. In fact, most studies do not show any significant increase in atopy after RSV bronchiolitis. This suggests that the increased risk of wheezing after RSV is not linked to an increased risk of atopy. There are some indications that infants who develop severe RSV and subsequent wheezing may have aberrations that predate the RSV infection. To decide whether respiratory syncytial virus bronchiolitis causes, or is associated with the respiratory sequelae (or with subsequent allergy), it will be necessary to conduct prospective, randomized studies, where the cytokine profile prior to bronchiolitis onset is known. Such studies should preferably include some form of intervention against respiratory syncytial virus. A more complete understanding of the risk factors for severe respiratory syncytial virus infection and the role of respiratory syncytial virus infection in the initiation of asthma is needed as a basis for large-scale and cost-effective programmes to prevent respiratory syncytial virus-related morbidity.