RSV infection involves smaller airways in the lung, which in younger patients can lead to difficulties with breathing and the supply of oxygen to the body. Outbreaks of RSV occur around the world every year and have an unusually predictable and regular pattern. In temperate climates, RSV usually produces midwinter epidemics, with more children becoming ill in January to March. An epidemic of RSV in a community can be detected by an abrupt rise in the number of hospital admissions of young children with acute lower respiratory tract disease. Reinfections with RSV occur throughout life.
Most children have only one infection associated with disease of the lung.
The most severe illness occurs in young infants, although disease in the immediate newborn period is uncommon. Antibodies from the mother may protect newborns from serious illness. Children with underlying heart or lung disease, those who were born prematurely and those with problems with their immune systems are at increased risk of severe disease due to RSV infection. RSV spreads easily from person to person through respiratory secretions. Spread within families is very high.