Update: respiratory syncytial virus activity--United States, 1998-1999 season.

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract disease in infants and young children worldwide. In temperate climates, RSV infections occur primarily during annual outbreaks, which peak during winter months . In the United States, RSV activity is monitored by the National Respiratory and Enteric Virus Surveillance System (NREVSS), a voluntary, laboratory-based system. This report summarizes trends in RSV activity reported to NREVSS during July 1998 June 1999 and presents preliminary surveillance data during July 1-November 12, 1999, which show that RSV community outbreaks are becoming widespread.