RSV Respiratory syncytial virus (RSV) infection is a viral disease of the lungs. It is one of the most important causes of lower respiratory tract illness in infants and young children. RSV is spread by contact with droplets from the nose or throat of an infected person Respiratory syncytial virus (RSV) infection is one of the most important causes of lower respiratory illness in infants and young children. Illness usually starts within 3 to 5 days of infection. Approximately ...