BRONCHIOLITIS

Smyth, R.L.; Brearey, S.P.

Bronchiolitis is a common respiratory tract infection usually affecting infants and young children during annual epidemics. It is characterized by wheeze, respiratory distress, and poor feeding. Respiratory syncytial virus (RSV) is the most common cause for bronchiolitis and is amongst the most important pathogens causing respiratory infection in infants worldwide. The healthcare burden of bronchiolitis is large, due to large numbers of hospitalized infants and the high risk of nosocomial spread during epidemics. Most children will suffer only mild, short-lived symptoms. A small proportion will need admission to hospital, where treatment is generally supportive until the illness resolves. Some will require ventilatory support for which mortality can be up to 10%. Infants at high risk of severe disease include those born prematurely, those with chronic lung disease, and immunocompromised infants. RSV infects ciliated epithelial cells, causing sloughing of the epithelium, cytokine and inflammatory mediator release, increases in mucus production, and interstitial edema. Clinical manifestations of bronchiolitis are a combined result of viral toxicity and the immune response to infection. Innate immune responses are important to the pathogenesis of bronchiolitis, as severe infection tends to occur after maternal antibody protection has waned and before the infant's adaptive immune responses have matured. Immunoprophylaxis, in the form of intramuscular anti-RSV IgG(1), is effective in reducing rates of hospitalization for high-risk infants.