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Weekly Report: Influenza Summary Update
Week ending January 13, 2001-Week 2

The following information may be quoted:


During week 2 (January 7-13, 2001)*, 15 % of the specimens tested by WHO and NREVSS laboratories were positive for influenza. 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 7 of 9 surveillance regions. The proportion of deaths attributed to pneumonia and influenza was 7,7 %. This percentage is below the epidemic threshold for this time of year. Two state and territorial health departments reported widespread influenza activity**, 21 reported regional influenza activity, and 26 reported sporadic activity.

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

During week 2, WHO and NREVSS laboratories reported 1 260 specimens tested for influenza viruses, of which 186 (15 %) were positive. Thirty-two (17 %) were influenza A (H1N1) viruses, 97 (52 %) were unsubtyped influenza A viruses, and 57 (31 %) were influenza B viruses. Between 20 % and 25 % of specimens tested for influenza over the past 3 weeks (weeks 52-2) in the New England and West South Central regions*** were positive for influenza. In 5 regions (East North Central, Mountain, South Atlantic, Pacific, and West North Central), the percentage of specimens testing positive for influenza in the past 3 weeks ranged from 9 % to 15 %. The percentage of specimens testing positive in the Mid-Atlantic and East South Central regions was 5 % or less.

Since October 1, WHO and NREVSS laboratories have tested a total of 26 789 specimens for influenza viruses, and 1 545 (6 %) have yielded influenza virus isolates. Of the 1 545 isolates identified, 1 132 (73 %) were influenza type A and 413 (27 %) were influenza type B. Of the 1 132 influenza A viruses, 457 (40 %) have been subtyped; 441 (96 %) were A (H1N1) and 16 (4 %) were A (H3N2). Influenza A viruses have predominated (range 63 % to 86 %) in 6 regions (East North Central, Mountain, New England, South Atlantic, West North Central, and West South Central), and influenza B viruses have predominated (range 60 % to 71 %) in the remaining 3 regions (Mid-Atlantic, East South Central, and Pacific).

 Influenza Virus Isolated

Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 86 influenza viruses received from U.S. laboratories since October 1. Of the 56 influenza A (H1N1) isolates that have been characterized, 53 (95 %) were similar to A/New Caledonia/20/99, the H1N1 component of the 2000-01 influenza vaccine, and 3 (5 %) were similar to A/Bayern/07/95. Although A/Bayern-like viruses are antigenically distinct from the A/New Caledonia-like viruses, the A/New Caledonia/20/99 vaccine strain produces high titers of antibody that cross-react with A/Bayern/07/95-like viruses. Of the 10 influenza A (H3N2) viruses and the 20 influenza B viruses that have been characterized, all were antigenically similar to vaccine strains A/Panama/2007/99 (H3N2) and B/Beijing/184/93, respectively.

Pneumonia and Influenza (P&I) Mortality:

During week 2, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 7,7 %. This percentage is below the epidemic threshold of 8,5 % for week 2.

Pneumonia And Influenza Mortality

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Influenza Morbidity Reports from U.S. Sentinel Physicians*:

During week 2, 2 % of patient visits to U.S. sentinel physicians were due to influenza-like illness (ILI). The percentage of patient visits for ILI was above baseline levels in the Pacific region (6 %) and West South Central region (4 %).

Bar Chart for Influenza-like Illness

Influenza Activity as Assessed by State and Territorial Epidemiologists**:

Influenza activity was reported as widespread in 2 states (Rhode Island and Virginia) and regional in 21states (Alabama, Arizona, Colorado, Connecticut, Idaho, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Minnesota, Mississippi, Nevada, North Carolina, Oregon, Tennessee, Texas, Utah, Washington, and Wyoming). Twenty-six states reported sporadic influenza activity and 1 state 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: January 18, 2001


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