Thorax 1989;44:1-5 Editorial Acute bronchiolitis in infancy: treatment and

prognosis Acute bronchiolitis is the most common severe lower respiratory tract infection of infancy. About 2 % of all babies born in the previous 12 months will be admitted to hospital with the condition. ' Although the clinical picture can be produced by various viruses, including influenza and parainfluenza virus and the adeno-viruses, most cases, particularly during the winter epidemics, are due to infection with the respiratory syncytial virus. There has been considerable and, to some extent, unresolved dispute about the features necessary for the diagnosis. There is a tendency, especially in North America,2 to apply the term to all babies who have signs of acute lower airways obstruction in infancy, particularly if the baby has previously been well. This grouping will inevitably include an appreciable num-ber of babies with asthma. This can largely be avoided if the term is limited to babies who have tachypnoea, hyperinflation, and fine crepitations at some time during the course of the illness,3 after pneumonia and heart failure have been excluded by chest radiography. Although differentiating between acute bronchiolitis and infantile asthma currently has little, if any, influence on management, long term studies have shown that the outcome is different, and it is important if long term epidemiological studies are to be carried out that the diagnosis is refined as much as possible. Prognosis Although the infants look critically ill on presentation, with gross hyperinflation and recession and often with cyanosis and sometimes carbon dioxide retention, nearly all make what appears to be a dramatic and complete recovery within five to 10 days. There is, however, increasing evidence to show that acute bronchiolitis is associated with a considerable amount of morbidity persisting for many years