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Weekly Report: Influenza Summary Update

Week ending January 12, 2002-Week 2

The following information may be quoted:

Synopsis:

During week 2 (January 6-12, 2002)*, 96 (8.9%) of 1076 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 1.6%, which is below the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 7.0%, which is below the epidemic threshold of 8.1% for week 2. Three state and territorial health departments reported widespread influenza activity, 12 reported regional activity, 33 reported sporadic activity, and 2 states reported no influenza activity **.

Laboratory Surveillance*:

During week 2, WHO and NREVSS laboratories reported 1076 specimens tested for influenza viruses. Nineteen influenza A (H3N2) viruses and 77 unsubtyped influenza A viruses were identified.

Since September 30, WHO and NREVSS laboratories have tested a total of 22,888 specimens for influenza viruses and 904 (3.9%) were positive. Of the 904 isolates identified, 885 (98%) were influenza A viruses and 19 (2%) were influenza B viruses. Three hundred and fifty-one (40%) of the 885 influenza A viruses identified have been subtyped; 345 (98%) were influenza A (H3N2) viruses and 6 (2%) were influenza A (H1N1) viruses. Three hundred and ninety-seven (44%) of the 904 U.S. isolates were reported from the Pacific region.*** Two hundred and twelve (23%) of the 904 isolates reported were identified in Hawaii and 153 (17%) were identified in Alaska. Forty-one states have reported laboratory-confirmed influenza.

Influenza Virus Isolated


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Antigenic Characterization:

CDC antigenically characterized 10 influenza viruses collected in September and 60 collected since October: 65 influenza A (H3N2) viruses, 4 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 2, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.0%. This percentage is below the epidemic threshold of 8.1% for week 2.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 2, 1.6% 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 0.7% to 3.6%.*** Due to wide variability in regional level data, it is not possible to calculate region-specific baselines and it is not appropriate to apply the national baseline to regional level data.

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

Influenza activity was reported as widespread in 3 states (Colorado, Pennsylvania, and Utah) and regional in 12 states (Alaska, Connecticut, Louisiana, Maryland, Massachusetts, Nebraska, New York, Tennessee, Texas, Vermont, Virginia, and Washington) and New York City. Thirty-three states and Washington, DC reported sporadic activity, and 2 states reported no influenza activity.

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 January 17, 2002

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