Update: influenza activity--United States, 1998-99 season.

In collaboration with the World Health Organization (WHO), its collaborating laboratories, and state and local health departments, CDC conducts surveillance to monitor influenza activity and to detect antigenic changes in the circulating strains of influenza viruses. This report summarizes influenza surveillance in the United States from October 4, 1998, to January 9, 1999, which indicates that overall influenza activity was low.