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Weekly Report: Influenza Summary Update

Week ending October 20, 2001-Week 42

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The following information may be quoted:

Synopsis:

During week 42 (October 14-20, 2001)*, none 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 (ILI) overall was 1.5%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.4%. Twelve state and territorial health departments reported sporadic influenza activity and 36 reported no influenza activity**.

Laboratory Surveillance*:

During week 42, WHO and NREVSS laboratories reported 463 specimens tested for influenza viruses. No influenza isolates were identified.

Since September 30, WHO and NREVSS laboratories have tested a total of 1,936 specimens for influenza viruses and 11 (1%) were positive. Of the 11 isolates identified, 4 were influenza A (H3N2) viruses, 6 were unsubtyped influenza A viruses, and 1 was an influenza B virus. Influenza A isolates have been identified in Alaska, Arizona, New York, and Texas. The influenza B isolate was identified in Texas.

Influenza Virus Isolated
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Antigenic Characterization:

CDC has antigenically characterized 2 influenza A (H3N2) viruses collected in the United States since October 1. Both viruses were antigenically similar to the vaccine strain A/Panama/2007/99 (H3N2).

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 42, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.4%. This percentage is below the epidemic threshold of 6.9% for week 42.

Prior to the 1999-2000 season, a new case definition for a P&I death was introduced in the 122 Cities Mortality Reporting System. During the summer of 2000, the baseline and epidemic threshold were manually adjusted to take into account these changes in the case definition. At this point, sufficient data have been collected using the new case definition to allow us to readjust the P&I mortality baseline and epidemic threshold for the 2001-02 season.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 42, 1.5% of patient visits to U.S. sentinel physicians were due to ILI. On a regional level***, the percentage of visits for ILI ranged from 0.3% to 2.2%.

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

Influenza activity was reported as sporadic in 12 states (Alaska, Indiana, Kansas, Kentucky, Minnesota, Missouri, New Mexico, New York, Ohio, Pennsylvania, West Virginia, and Wyoming) and New York City. Thirty-six states and Washington, DC reported no influenza activity, and 2 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 October 25, 2001

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