The Etiology of Respiratory Illnesses Occurring in Infancy and Childhood

Twenty-six agents were recovered from pharyngeal samples obtained from 194 infants and children ill of respiratory infections. Fourteen were parainfluenza, five were adenoviruses, and two were influenza A2 viruses; five agents were unidentified. Seroconversion against homologous virus occurred in 6 of 12 patients. In four of six patients ill of croup, the infection was associated with parainfluenza, type 1, virus. Respiratory syncytial virus was not associated with bronchiolitis, and was associated with pneumonia only in about 10% of patients. Essentially similar seroconversion rates were obtained for other respiratory syndromes and for the small group of patients with nonrespiratory illnesses. Although seroconversion was obtained for influenza C virus, particularly in patients with bronchiolitis and pneumonia, the large fraction of individuals seropositive during early infancy, and the high frequency of seropositives in subsequent age groups suggests that the virus may have a pathogenic potential not yet fully appreciated. Influenza A2 and B viruses were active during the period of study, apparently recruiting those still at risk. The results of this study failed to associate any one of the 10 respiratory viruses with a major proportion of the separate clinical syndromes. Probably too much has been expected in the delineation of selective anatomical sites of injury by some of these viruses! Information is needed also on the combined effects of pathogenic bacteria and viruses in the pathogenesis of respiratory diseases.