title: Influenza surveillance--United States, 1992-93 and 1993-94.
abstract: OBJECTIVE
  CDC conducts active surveillance annually from October through May on the emergence and spread of influenza virus variants and the impact of influenza-related morbidity and mortality. Influenza activity is also monitored throughout the year by passive surveillance.
  
  
  METHODS
  This report summarizes U.S. influenza surveillance from October 1992 through May 1994.
  
  
  METHODS
  Influenza surveillance comprises four components, three of which provide weekly data from October through May: a) state and territorial epidemiologists provide estimates of local influenza activity; b) approximately 140 sentinel physicians report their total number of patient visits and the number of cases of influenza-like illness; and c) approximately 70 collaborating laboratories of the World Health Organization (WHO) report weekly influenza virus isolations and submit selected influenza isolates to CDC for antigenic analysis. Throughout the year, vital statistics offices of 121 cities report deaths related to pneumonia and influenza (P&I), providing an index of the impact of influenza on mortality.
  
  
  RESULTS
  Influenza B viruses predominated during the 1992-93 influenza season, but influenza A(H3N2) isolates increased and were associated with outbreaks in nursing homes at the end of the season. The increase in influenza A(H3N2) activity was associated with a rise in P&I-related mortality. Preseason outbreaks of influenza A(H3N2) virus were reported during August and September 1993 in Louisiana. In the past, preseason outbreaks of influenza have been associated with earlier than usual epidemic-level activity. During the 1993-94 influenza season, activity rose during November and December and peaked earlier than usual, during the last week of December and the first week of January; influenza A(H3N2) viruses predominated.
  
  
  CONCLUSIONS
  The change in predominance from influenza B to influenza A in the spring of 1993 emphasizes the importance of annual influenza surveillance. Although influenza vaccine is effective against both influenza A and B, the antiviral drugs amantadine and rimantadine are effective only against influenza A. Outbreaks during the summer of 1993 emphasize that influenza should be considered a possible cause of respiratory infections during summer and early autumn.
  
  
  CONCLUSIONS
  Surveillance data were provided weekly throughout the influenza season to public health officials, WHO, and health-care providers.
authors.affiliation: Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, USA.
authors.forename: L
authors.initials: L
authors.lastname: Brammer
authors.forename: K
authors.initials: K
authors.lastname: Fukuda
authors.forename: N
authors.initials: N
authors.lastname: Arden
authors.forename: L M
authors.initials: LM
authors.lastname: Schmeltz
authors.forename: L
authors.initials: L
authors.lastname: Simonsen
authors.forename: A
authors.initials: A
authors.lastname: Khan
authors.forename: H L
authors.initials: HL
authors.lastname: Regnery
authors.forename: L B
authors.initials: LB
authors.lastname: Schonberger
authors.forename: N J
authors.initials: NJ
authors.lastname: Cox
mesh_terms: D006801:Humans; D009980:Influenza A virus; D009981:Influenza B virus; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D012621:Seasons; D014481:United States / Q000453:epidemiology
chemical_list: D007252:Influenza Vaccines