The epidemiology of bronchiolitis.

From the data presented a composite epidemiologic picture of bronchiolitis can be drawn. If one uses a large brush the picture would be that of a common, mild disease during the first 2 years of life, due primarily to RSV and occurring predominantly in males during the winter and spring months. If the drawing is examined more closely, however, a more complex picture is seen. Our data suggest that this syndrome is very common indeed if children are followed closely and examined carefully, but under these circumstances is quite mild. If more strict criteria, such as hospitalization, are applied for inclusion of patients with bronchiolitis a different age distribution is seen. Most children who become severely ill are under 6 months of age and in this group morbidity and mortality are high. Agents other than RSV cause bronchiolitis but in these instances the age occurrence and seasonal occurrence are different from those seen with RSV disease. The predominance of bronchiolitis in males is striking. Our day care center data suggest that mild bronchiolitis occurs with equal sex frequency. This would suggest that the reason more boys are carried to the pediatrician or hospitalized is because they get sicker. Further studies on this phenomenon are in progress. Finally, our data suggest that many bronchiolitis cases from whom no agents were isolated were due to RSV. There is, however, a segment of bronchiolitis cases that occurs in the young child during all seasons which suggests that the young bronchiole may react to a variety of stimuli. This poses a real problem for the investigator of bronchiolitis; hopefully meaningful answers will be available soon.