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Weekly Report: Influenza Summary Update

Week ending January 4, 2003-Week 1

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The following information may be quoted:

Synopsis:

During week 1 (December 29, 2002 – January 4, 2003)*, 25 (2.2%) of the specimens tested by World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) laboratories were positive for influenza. The proportion of patient visits to sentinel providers for influenza-like illness (ILI) overall was 2.0%, which is greater than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.8%. Seven state and territorial health departments reported regional influenza activity, 31 reported sporadic activity, and 11 reported no influenza activity**.

Laboratory Surveillance*:

During week 1, WHO and NREVSS laboratories reported 1,147 specimens tested for influenza viruses, of which 25 (2.2%) were positive. Three influenza A (H1)† virus, one influenza A (H3N2) virus, eight unsubtyped influenza A viruses, and 13 influenza B viruses were identified. During the past 3 weeks (weeks 51-1), 13.1% of the specimens tested for influenza in the West South Central region*** were positive. Between 0.4% and 5.0% of specimens tested for influenza were positive during the past 3 weeks in the East North Central, Mid-Atlantic, Mountain, New England, Pacific, South Atlantic, and West North Central regions.

Since September 29, WHO and NREVSS laboratories have tested a total of 23,976 specimens for influenza viruses and 321 (1.3%) were positive. Of the 321 viruses identified, 90 (28%) were influenza A viruses and 231 (72%) were influenza B viruses. Twenty-four (27%) of the 90 influenza A viruses have been subtyped; 18 (75%) were influenza A (H1)† viruses and 6 (25%) were influenza A (H3N2) viruses. One hundred thirty-three (58%) of the 231 influenza B viruses were identified in Texas. Twenty-five states have reported laboratory-confirmed influenza. Influenza A and influenza B viruses have been identified in Arizona, California, Indiana, Louisiana, Missouri, Nebraska, New York, North Carolina, South Carolina, Texas, and Virginia. Florida, Hawaii, Massachusetts, Minnesota, New Jersey, Oregon, South Dakota, Washington, and Wisconsin have reported only influenza A viruses, and Arkansas, Kansas, Nevada, New Hampshire, and Oklahoma have reported only influenza B viruses. Influenza A viruses were reported more frequently than influenza B viruses (range 61% - 89%) in the East North Central, Mid-Atlantic, New England, Pacific, and South Atlantic regions, and influenza B viruses were reported more frequently than influenza A viruses (range 80% - 88%) in the Mountain, West North Central, and West South Central regions. The East South Central region has not reported any influenza viruses.

 Influenza Virus Isolated

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Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 42 influenza viruses submitted by U.S. laboratories since September 29: twenty-six influenza B viruses, four influenza A (H3N2) viruses, and 12 influenza A (H1)† viruses. Eleven of the influenza A (H1) viruses had the N1 neuraminidase and one had the N2 neuraminidase. The influenza B viruses, the A (H3N2) viruses, and the hemagglutinin proteins of the A (H1N1) and A (H1N2) viruses were similar antigenically to those of the corresponding vaccine strains B/Hong Kong/330/01, A/Panama/2007/99 (H3N2), and A/New Caledonia/20/99 (H1N1), respectively.

Click here for more information about influenza A (H1N2) viruses

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 1, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.8%. This percentage is below the epidemic threshold of 8.0% for week 1.

<Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 1, 2.0% of patient visits to U.S. sentinel providers were due to ILI. This percentage is greater than the national baseline of 1.9%. On a regional level***, the percentage of visits for ILI ranged from 0.6% to 4.1%. Due to wide variability in regional level data, 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 regional in 7 states (Arkansas, Kansas, New York, Oklahoma, Tennessee, Texas, and Virginia) and New York City. Thirty-one states and Washington D.C. reported sporadic activity, 11 states reported no 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.

†Includes both the A (H1N1) and A (H1N2) influenza virus subtypes. The influenza A (H1N2) strain appears to have resulted from the reassortment of the genes of currently circulating influenza A (H1N1) and A (H3N2) subtypes. Because the hemagglutinin proteins of the A (H1N2) viruses are similar to those of the currently circulating A (H1N1) viruses and the neuraminidase proteins are similar to those of the currently circulating A (H3N2) viruses, the 2002-03 influenza vaccine should provide protection against A (H1N2) viruses.

*** 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 9, 2003

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