Background: Viral acute respiratory infections (ARI) continues to be a significant cause of healthcare visits in young children. We evaluated the clinical presentation and disease severity of common respiratory viruses associated with medically attended ARI in infants.

Results: In total, 364 participants were enrolled, and 361 (99%) had nasal swabs collected and tested. Overall, mean age was 6±3.3 months, 50% were female, 45% White, and 27% Hispanic. Of the 295 (82%) virus-positive specimens; the three most common viruses were rhinovirus/enterovirus (RV/EV), respiratory syncytial virus (RSV), and influenza (flu) [124, 101, and 44, respectively]. Compared to virus-negative infants, virus-positive infants were more likely to have more severe ARI symptoms and to be admitted to the intensive care unit (Table 1). Compared to other virus-positive infants: RV/EV-positive infants were more likely to be White, attend daycare, but less likely to present with respiratory distress, or require oxygen or admission; flu-positive infants were older and more likely to have systemic symptoms rather than ARI symptoms, and RSV-positive infants were more likely to present with respiratory distress, receive oxygen and be hospitalized (Table 1).

Conclusions: The majority of ARI in infants are due to respiratory viruses, with RSV, RV/EV, and flu accounting for over three-quarters of these viruses. The clinical presentations and disease severity differed across the clinical settings and the three main viruses, with RSV being most severe. To decrease the burden of medically attended viral ARI, preventive measures (i.e., developing new vaccines and antivirals), refining current vaccination strategies, and infection control measures are needed.