Viral respiratory infections.

Viral infections constitute more than 60% of acute lower respiratory illnesses. Respiratory syncytial virus (RSV) and parainfluenza viruses are the most frequent etiologic agents. After transmission by large droplet aerosol or direct contact, the viruses gain entry into host cells through specific viral surface proteins; subsequently, pathogenetic mechanisms cause tissue injury and result in clinical disease. In the intensive care unit the mainstay of treatment is primarily supportive. Nonspecific treatment may include nebulized beta-agonists, aminophylline, and steroids. Ribavarin is the only specific antiviral agent approved for respiratory syncytial virus infection but its efficacy remains controversial. New therapies and vaccines offer hope for improved outcome from viral respiratory infections such as RSV.