Virus Type and Genomic Load in Acute Bronchiolitis: Severity and Treatment Response With Inhaled Adrenaline

Background. Acute bronchiolitis frequently causes infant hospitalization. Studies on different viruses or viral genomic load and disease severity or treatment effect have had conflicting results. We aimed to investigate whether the presence or concentration of individual or multiple viruses were associated with disease severity in acute bronchiolitis and to evaluate whether detected viruses modified the response to inhaled racemic adrenaline. Methods. Nasopharyngeal aspirates were collected from 363 infants with acute bronchiolitis in a randomized, controlled trial that compared inhaled racemic adrenaline versus saline. Virus genome was identified and quantified by polymerase chain reaction analyses. Severity was assessed on the basis of the length of stay and the use of supportive care. Results. Respiratory syncytial virus (83%) and human rhinovirus (34%) were most commonly detected. Seven other viruses were present in 8%-15% of the patients. Two or more viruses (maximum, 7) were detected in 61% of the infants. Virus type or coinfection was not associated with disease severity. A high genomic load of respiratory syncytial virus was associated with a longer length of stay and with an increased frequency of oxygen and ventilatory support use. Treatment effect of inhaled adrenaline was not modified by virus type, load or coinfection. Discussion. In infants hospitalized with acute bronchiolitis, disease severity was not associated with specific viruses or the total number of viruses detected. A high RSV genomic load was associated with more-severe disease.