Respiratory syncytial virus bronchiolitis: clinical aspects and epidemiology.

Sixty to ninety percent of the clinical syndrome of bronchiolitis is caused by respiratory syncytial virus (RSV) infection. RSV epidemiology has several unusual characteristics. RSV infects nearly all infants in the first year of life, with a peak incidence of hospitalized infants with bronchiolitis between 2-6 months of age. It is the only virus that causes most severe disease during the first month of life, i.e. at a time when maternal antibodies are present. Lower respiratory tract infections caused by RSV are limited to children younger than 3 yrs but symptomatic infection with RSV occurs throughout life. Infants with cardiac disease as well as infants with bronchopulmonary dysplasia are especially prone to develop severe RSV bronchiolitis. Apnoea is a complication that occurs in infants younger than 3 months and after a history of apnoea of prematurity. Nosocomial infection is a major health problem. Hospital staff may spread the infection by becoming infected and shedding the virus, or by carrying contaminated secretions between patients. Classical teaching has been that the prevalence of wheeze is high after acute viral bronchiolitis in infancy, but recent data suggest that infants with already lower maximal expiratory flows at functional residual capacity are more prone to develop wheeze at the time of RSV bronchiolitis.