Viral Codetection and Clinical Outcomes of Infants Hospitalized With Bronchiolitis: A Multicenter Cohort Study.

Background: The simultaneous identification of multiple respiratory viruses is common in infants hospitalized with respiratory tract infections. Respiratory syncytial virus (RSV) is one of the main pathogens in bronchiolitis, although codetection of rhinovirus, influenza and other respiratory viruses may occur in about one-third of cases. The relevance of viral codetection on disease severity is still controversial. This multicenter cohort study aimed to assess the clinical outcomes of infants under 24 months hospitalized with bronchiolitis, comparing those testing positive for RSV alone, RSV plus another virus and ≥2 viruses distinct from RSV.

Methods: Data were collected across 13 hospitals in Lombardy, Italy, both in the prepandemic and pandemic years. Random effect regression models were also employed to test the association between 3 groups (infants testing positive for RSV alone, RSV plus another respiratory virus and no RSV but ≥2 respiratory viruses other than RSV) and course of bronchiolitis, adjusted for potential confounders.

Results: Among 1788 infants, 86.7% tested positive for RSV alone, 6.9% for RSV plus another virus and 6.3% for ≥2 other viruses. Significant differences were found in clinical outcomes: infants with multiple non-RSV viruses had shorter oxygen supplementation, intensive care and hospital stay compared with those with RSV alone. Notably, codetection of RSV and another virus was associated with a higher risk of radiologically confirmed pneumonia, whereas detection of ≥2 non-RSV viruses was inversely associated with pneumonia.

Conclusions: These findings point out that codetection of viruses other than RSV is associated with milder disease courses than detection of RSV alone in infants with bronchiolitis. On the other hand, patients with RSV and another virus are at higher risk of pneumonia than infants affected by RSV alone. Further research is required to understand the underlying mechanisms and optimize management strategies in infants with bronchiolitis testing positive for multiple viruses.