Influenza activity--United States and worldwide, April-October 2000.

During October 1999-May 2000, influenza A(H3N2), A(H1N1), and B viruses were identified in the Northern Hemisphere. Influenza A(H3N2) predominated, but the number of influenza A(H1N1) viruses increased toward the end of the influenza season in the Northern Hemisphere. Since April, influenza A viruses have predominated in the Southern Hemisphere and tropical regions, but influenza B viruses also have been identified. This report summarizes influenza activity in the United States and worldwide from April 2000 through October 2000.