Respiratory syncytial virus (RSV) is the most impoant cause of pneumonia and bronchiolitis in infants. The infection is localized to the respiratory tract. The virus can be detected rapidly by immunofluorescence on smears of respiratory epithelium. In older children, the infection resembles the common cold. Aerosolized ribavirin is recommended for severely ill hospitalized infants. Rotavirus causes diarrhea. Coxsackievirus causes hand, foot, and, mouth disease.