Population-based trends and underlying risk factors for infant respiratory syncytial virus and bronchiolitis hospitalizations.

OBJECTIVE: Respiratory syncytial virus (RSV) is a common pathogen during infancy, with the potential to cause serious disease and mortality in high-risk groups. The objective of this study was to characterize trends of RSV and bronchiolitis hospitalizations in the first year in a population-based cohort and assess differences in trends according to risk status.

METHODS: Using an observational retrospective cohort design, we examined a California population-based dataset of vital statistics linked to hospital discharge data for up to 1 year after birth from 1997-2011. Infants were categorized by medical condition and then by gestational age. Medical conditions of interest included chronic lung disease, certain congenital heart diseases, or others known to affect risk for developing severe bronchiolitis. The primary outcome was hospitalization due to RSV; secondary outcome was hospitalization for unspecified bronchiolitis (UB) not coded as RSV. Annual person-year rates were calculated for infants