Objectives: Respiratory syncytial virus (RSV) is a major cause of hospitalization in young children, but there are little data on RSV infections in early childhood in the community. We conducted a prospective population-based birth-cohort study to determine the rates and characteristics of RSV infections in young children.

Methods: We followed 923 children for acute respiratory infections (ARIs) from birth to age 24 months with daily diaries and study clinic visits. Nasal swab samples were obtained at the onset of ARIs and analyzed for RSV by RT-PCR and antigen tests. The rates of RSV infections and associated outcomes were estimated.

Results: RSV was detected in 289 (6%) of 4728 ARIs with a nasal sample. The mean estimated annual rate of RSV infections was 37 (95% confidence interval [CI], 35–38) per 100 children at age 0–24 months. For RSV-associated outcomes, the estimated annual rates per 100 children were 34 (95% CI, 32–37) physician visits, 16 (95% CI, 15–17) antibiotic treatments, 12 (95% CI, 11–13) acute otitis media, and 6 (95% CI, 4–7) wheezing illnesses. The prevalence of RSV was 0.6% in asymptomatic children.

Conclusions: RSV infections impose a high burden of disease in healthy young children in the community.