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Influenza Summary Update

(Week ending December 23, 2000-Week 51)

The following information may be quoted:

Synopsis: During week 51 (December 17-23, 2000)*, 65 of the specimens tested by WHO and NREVSS laboratories were positive for influenza type A virus and 16 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 7.2%. This percentage is below the epidemic threshold for this time of year. Seven state and territorial health departments reported regional influenza activity**, 34 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 51, WHO and NREVSS laboratories reported 830 specimens tested for influenza viruses, of which 81 (10%) were positive. Twelve were influenza A(H1N1) viruses, 53 were unsubtyped influenza A viruses, and 16 were influenza B viruses.

Since October 1, WHO and NREVSS laboratories have tested a total of 15,364 specimens for influenza viruses, and 460 (3%) have yielded influenza virus isolates. Of the 460 isolates identified, 340 (74%) were influenza type A and 120 (26%) were influenza type B. Of the 340 influenza A viruses, 201 (59%) have been subtyped; 192 (96%) were A (H1N1) and 9 (4%) were A (H3N2). Three hundred and eighty-one (83%) of the 460 U.S. isolates have been reported from the West South Central*** [248 (65%)], Pacific [79 (21%)], and South Atlantic [54 (14%)] regions. Influenza A (H1N1) viruses have predominated in the West South Central and South Atlantic regions. In the West South Central region, the majority [223 (90%)] of isolates reported were from Texas. In the Pacific region, influenza type B viruses accounted for 65 (82%) of the 79 isolates reported. Fifty-three (67%) of the 79 influenza B viruses reported in the Pacific region were from Alaska.

Influenza Viruses Isolated by

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 51, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 7.2%. This percentage is below the epidemic threshold of 8.3% for week 51.

Pneumonia and Influenza Mortality 





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Influenza Morbidity Reports from U.S. Sentinel Physicians *: During week 51, 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. Five percent of patient visits to sentinel physicians in the Pacific region were due to ILI.

Bar Chart for Influenza-like Illness

Influenza Activity as Assessed by State and Territorial Epidemiologists**: Influenza activity was reported as regional in Colorado, Kentucky, New York, Oregon, Tennessee, Texas, and Virginia. Thirty-four states reported sporadic influenza activity, 7 states reported no influenza activity, and 2 states did not report.

Usmap for Weekly Influenza Activity

* 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 28, 2000

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National Center for Infectious Diseases
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