Abstract
Respiratory viral infections are associated with significant morbidity and mortality in children < 5 years of age worldwide. Among all respiratory viruses, respiratory syncytial virus (RSV) is the world's leading cause of bronchiolitis and pneumonia in young children. There are known populations at risk for severe disease but the majority of children who require hospitalization for RSV infection are previously healthy. Viral and host factors have been associated with the pathogenesis of RSV disease; however, the mechanisms that explain the wide variability in the clinical presentation are not completely understood. Recent studies suggest that the complex interaction between the respiratory microbiome, the host's immune response and the virus may have an impact on the pathogenesis and severity of RSV infection. In this review, we summarize the current evidence regarding the epidemiologic link, the mechanisms of viral-bacterial interactions, and the associations between the upper respiratory tract microbiome and RSV disease severity.