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Weekly Report: Influenza Summary Update
Week ending January 6, 2001-Week1

The following information may be quoted:


During week 1 (December 31, 2000 – January 6, 2001)*, 12% 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 7.5%. This percentage is below the epidemic threshold for this time of year. Two state and territorial health departments reported widespread influenza activity**, 11 reported regional influenza activity, and 35 reported sporadic activity.

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

During week 1, WHO and NREVSS laboratories reported 1,182 specimens tested for influenza viruses, of which 138 (12%) were positive. Twenty (15%) were influenza A (H1N1) viruses, 2 (1%) were influenza A (H3N2) viruses, 88 (64%) were unsubtyped influenza A viruses, and 28 (20%) were influenza B viruses. Twenty-two percent of specimens tested for influenza over the past 3 weeks (weeks 51-1) in the West South Central*** region were positive. In 3 regions (Mountain, New England, and Pacific), the percentage of specimens testing positive for influenza in the past 3 weeks ranged from 10% to 15%. The percentage of specimens testing positive in the remaining 5 regions (East North Central, East South Central, Mid-Atlantic, South Atlantic, and West North Central) ranged from 3% to 7%.

Since October 1, WHO and NREVSS laboratories have tested a total of 23,982 specimens for influenza viruses, and 1,205 (5%) have yielded influenza virus isolates. Of the 1,205 isolates identified, 894 (74%) were influenza type A and 311 (26%) were influenza type B. Of the 894 influenza A viruses, 336 (38%) have been subtyped; 322 (96%) were A (H1N1) and 14 (4%) were A (H3N2). Influenza A viruses have predominanted (range 55% 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 69%) in the remaining 3 regions (Mid-Atlantic, East South Central, and Pacific).

 Influenza Virus Isolated

Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 78 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 6 influenza A (H3N2) viruses and the 16 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 1, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 7.5%. This percentage is below the epidemic threshold of 8.5% for week 1.

Pneumonia And Influenza Mortality

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

During week 1, 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 (4%) and West South Central region (5%).

Percentage of Visits 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 11 states (Alabama, Arizona, Colorado, Nevada, North Carolina, Oregon, Pennsylvania, Tennessee, Texas, Utah, and Washington). Thirty-five states reported sporadic 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: January 11, 2001


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