Update: respiratory syncytial virus activity--United States, 1997-98 season.

Respiratory syncytial virus (RSV) is the single most important cause of serious lower respiratory tract disease in infants and young children worldwide. In temperate climates, infections primarily occur during yearly outbreaks that usually peak during the winter months. RSV activity in the United States is monitored by the National Respiratory and Enteric Virus Surveillance System (NREVSS), a voluntary, laboratory-based system. This report summarizes trends for RSV reported to NREVSS from July 1997 to June 1998 and presents preliminary surveillance data from July 1 to November 18, 1998.