What causes respiratory syncytial virus (RSV) infection?
Respiratory syncytial virus, or RSV, is a virus that attacks the mucous membranes of people’s respiratory tracts (the nose, throat, windpipe, and the bronchi and bronchioles (the air passages of the lungs). RSV is the most common respiratory pathogen in infants and young children. It has infected nearly all infants by the age of two years.