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Influenza Summary Update
(Week ending December 16, 2000-Week 50)

The following information may be quoted:

Synopsis: During week 50 (December 10-16, 2000)*, 59 of the specimens tested by WHO and NREVSS laboratories were positive for influenza type A virus and 12 were positive for influenza type B virus.  The proportion of patient visits to sentinel physicians for influenza-like illness was within baseline levels of 0 % to 3 % in the United States overall and in 8 of 9 surveillance regions.  The proportion of deaths attributed to pneumonia and influenza was 7,1 %.  This percentage is below the epidemic threshold for this time of year.  One state and territorial health department reported widespread influenza activity**, 6 reported regional activity, 35 reported sporadic activity, and 7 reported no influenza activity.  

U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) Collaborating Laboratory Reports*:

During week 50, WHO and NREVSS laboratories reported 1030 specimens tested for influenza viruses, of which 71 (7 %) were positive.  Twenty-six were influenza A(H1N1) viruses, 33 were unsubtyped influenza A viruses, and 12 were influenza B viruses.

Since October 1, WHO and NREVSS laboratories have tested a total of 14 010 specimens for influenza viruses, and 349 (2 %) have yielded influenza virus isolates.  Of the 349 isolates identified, 259 (74 %) were influenza type A and 90 (26 %) were influenza type B.  Of the 259 influenza A viruses, 182 (70 %) have been subtyped; 174 (96 %) were A (H1N1) and 8 (4 %) were A (H3N2).   Three hundred and thirteen (90 %) of the 349 U.S. isolates have been reported from the West South Central*** [208 (60 %)], Pacific [60 (17 %)], and South Atlantic [45 (13 %)] regions.  Influenza A(H1N1) viruses have predominated in the West South Central and South Atlantic regions.  In the West South Central region, the majority [186 (89 %)] of isolates reported were from Texas.  In the Pacific region, influenza type B viruses accounted for 50 (83 %) of the 60 isolates reported.  Thirty-eight (76 %) of the 50 influenza B viruses reported in the Pacific region were from Alaska. 

Influenza Virus Isolated (5091 bytes)

Antigenic Characterization of Viral Isolates:  CDC has antigenically characterized 33 influenza viruses received from U.S. laboratories since October 1: six influenza A(H3N2) viruses, 19 influenza A(H1N1) viruses, and eight influenza B viruses.  These viruses were antigenically similar to vaccine strains A/Panama/2007/99 (H3N2), A/New Caledonia/20/99 (H1N1), and B/Beijing/184/93, respectively. 

Pneumonia and Influenza (P&I) Mortality: During week 50, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 7,1 %.  This percentage is below the epidemic threshold of 8,2 % for week 50. 

Pneumonia and Influenza Mortality(4705 bytes) 





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Influenza Morbidity Reports from U.S. Sentinel Physicians *: During week 50, 2 % of patient visits to U.S. sentinel physicians were due to influenza-like illness (ILI).  The percentage of ILI was within baseline levels of 0 % to 3 % in 8 of 9 surveillance regions.   Four percent of patient visits to sentinel physicians in the Pacific region were due to ILI.

Bar Chart for Influenza-like Illness(3368 bytes)

 Influenza Activity as Assessed by State and Territorial Epidemiologists**: Influenza activity was reported as widespread in Texas and regional in Arkansas, Colorado, Georgia, Kentucky, Maryland, and Tennessee.  Thirty-five states reported sporadic influenza activity, 7 states reported no influenza activity,and 1 state did not report.

Usmap for Weekly Influenza Activity (8735 bytes)

* Reporting is incomplete for this week. Numbers may change as more reports are received.

** Influenza activity is defined as influenza-like illness and/or culture-confirmed influenza.

*** Surveillance Regions: New England (Connecticut, Maine, Massachusetts, New Hampshire, Vermont, Rhode Island); Mid-Atlantic (New Jersey, New York City, Pennsylvania, Upstate New York); East North Central (Illinois, Indiana, Michigan, Ohio, Wisconsin); West North Central (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota); South Atlantic (Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington, D.C., West Virginia); East South Central (Alabama, Kentucky, Mississippi, Tennessee); West South Central (Arkansas, Louisiana, Oklahoma, Texas); Mountain (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming); Pacific (Alaska, California, Hawaii, Oregon, Washington)

Report prepared: December 21, 2000

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National Center for Infectious Diseases
Centers for Disease Control and Prevention
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