Respiratory syncytial virus primarily causes infection of the respiratory tract, ranging from common cold to pneumonia.
The illness begins with infection of the upper respiratory tract, which manifests as common cold with marked rhinorrhea (running nose). This condition is most common in older chil-dren and adults. Incubation period varies from 4 to 5 days.
In infants, RSV causes a more severe lower respiratory tract illness, resulting in bronchiolitis or pneumonia. Clinically, the condition presents as cough, coryza, wheezing, rales, and low-grade fever (,101°F). Bronchiolitis is usually self-limiting, but may cause a serious disease in premature infants, in immu-nocompromised hosts, and in individuals with underlying lung diseases. Reinfection with the virus occurs throughout the life. However, with advancing age and recurrent infection, the RSV infection is confined more to the upper respiratory tract than the lower respiratory tract.