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Weekly Report: Influenza Summary Update

Week ending November 17, 2001-Week 46

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The following information may be quoted:

Synopsis:

During week 46 (November 11-17, 2001)*, 5 of 625 respiratory specimens tested by WHO and NREVSS laboratories were positive for influenza. The overall proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 1.2%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.6%, which is below the epidemic threshold of 7.3% for week 46. Four state and territorial health departments reported regional influenza activity, 19 reported sporadic influenza activity, and 24 reported no influenza activity**.

Laboratory Surveillance*:

During week 46, WHO and NREVSS laboratories reported 625 specimens tested for influenza viruses, of which 5 (0.8%) were positive. Two were influenza A (H3N2) viruses, 2 were unsubtyped influenza A viruses, and 1 was an influenza B virus.

Since September 30, WHO and NREVSS laboratories have tested a total of 6,171 specimens for influenza viruses and 50 (0.8%) were positive. Of the 50 isolates identified, 48 (96%) were influenza A viruses and 2 (4%) were influenza B viruses. Twenty (42%) of the 48 influenza A viruses identified have been subtyped and all were influenza A (H3N2) viruses. Influenza A isolates have been identified in Alaska, Arizona, Florida, Hawaii, Kentucky, Louisiana, New York, North Carolina, Texas, Utah, Washington, and Wisconsin. Influenza B isolates were identified in Michigan and Texas.

Influenza Virus Isolated
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Antigenic Characterization:

CDC antigenically characterized 10 influenza viruses collected in September and 8 collected in October: 15 influenza A (H3N2) viruses, 2 influenza A (H1N1) viruses, and 1 influenza B virus. All viruses were similar to the vaccine strains A/Panama/2007/99 (H3N2), A/New Caledonia/ 20/99 (H1N1), and B/Sichuan/379/99, respectively.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 46, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.6%. This percentage is below the epidemic threshold of 7.3% for week 46.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 46, 1.2% of patient visits to U.S. sentinel physicians were due to ILI. This is below the national baseline of 1.9%. On a regional level, the percentage of visits for ILI ranged from 0.1% to 2.6%.***

Bar Chart for Influenza-like Illness
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Influenza Activity as Assessed by State and Territorial Epidemiologists**:

Influenza activity was reported as regional in 4 states (Alaska, Colorado, New York, and Ohio) and sporadic in 19 states (Alabama, Arizona, California, Delaware, Florida, Georgia, Indiana, Iowa, Kansas, Maine, Michigan, Missouri, Nevada, New Mexico, North Dakota, Tennessee, Utah, West Virginia, and Wyoming), New York City, and Washington, DC. Twenty-four states reported no influenza activity, and 3 states did not report.

U. S. map 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 November 21, 2001

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