MMWR. 1993;42:131, 137-138 (1 figure omitted)
FROM SEPTEMBER 27, 1992, through February 13, 1993, the World Health Organization collaborating laboratories in the United States reported 1042 influenza virus isolates. For the weeks ending December 5,1992, through February 6, 1993, the ratio of specimens positive for influenza virus to total specimens submitted for respiratory virus testing increased from 0.02 to 0.2.
Weekly reports by state and territorial epidemiologists also indicated increasing levels of influenza-like illness (ILI) from December through mid-February. For the week ending February 13, 13 states reported sporadic ILI activity, 18 reported regional activity, and eight reported widespread activity.* Most laboratory-confirmed outbreaks of influenza occurred among school-aged populations, and most were associated with influenza type B.
From September 27,1992 (the beginning of the 1992-93 influenza surveillance period), through February 13, 1993, 965 (93%) of influenza virus isolates reported to CDC were influenza type B. Although influenza type A viruses