Objective:

To investigate the association between age at RSV hospitalization and the risk of subsequent bacterial pneumonia in children aged 0-5 years.

Key Findings:

• Children hospitalized for RSV at older ages face a higher risk of bacterial pneumonia later in childhood.
• The risk of bacterial pneumonia is highest shortly after RSV hospitalization and increases with age at first hospitalization.
• Children hospitalized between birth and 5 months of age are about five times more likely to be hospitalized for bacterial pneumonia shortly after RSV infection.
• Children hospitalized between 18 and 23 months of age are more than eight times as likely to be hospitalized for bacterial pneumonia shortly after RSV infection.

Interpretation:

Age-related differences in immune responses to RSV, such as variations in neutrophil activity, may contribute to increased susceptibility to bacterial complications, particularly in older infants and toddlers.

Limitations:

• Inability to adjust for potential confounding factors such as breastfeeding, day-care attendance, or comorbidities diagnosed after the neonatal period, which may influence susceptibility to respiratory infections.

Conclusion:

Preventing RSV infections during the first two years of life could reduce the risk of subsequent bacterial pneumonia, indicating the need for improved RSV prevention strategies that extend beyond early infancy.