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Weekly Report: Influenza Summary Update

Week ending November 23, 2002-Week 47

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The following information may be quoted:

Synopsis:

During week 47 (November 17-23, 2002)*, 21 (2.3%) 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 1.3%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 7.1%. Two state and territorial health departments reported regional influenza activity, 18 reported sporadic activity, and 27 reported no influenza activity**.

Laboratory Surveillance*:

During week 47, WHO and NREVSS laboratories reported 923 specimens tested for influenza viruses, of which 21 (2.3%) were positive. Two influenza A (H1)† viruses, 3 unsubtyped influenza A viruses, and 16 influenza B viruses were identified.

Since September 29, WHO and NREVSS laboratories have tested a total of 10,036 specimens for influenza viruses and 47 (0.5%) were positive. Of the 47 viruses identified, 20 (43%) were influenza A viruses and 27 (57%) were influenza B viruses. Seven (35%) of the 20 influenza A viruses have been subtyped; 6 were influenza A (H1)† viruses and 1 was an influenza A (H3N2) virus. Nine states have reported laboratory-confirmed influenza. Influenza A viruses have been identified in Florida, Hawaii, Louisiana, Nebraska, New York, North Carolina, South Carolina, and Virginia. Influenza B viruses have been identified in Louisiana, New York, South Carolina, and Texas. Of the 47 viruses reported, 26 (55%) were identified in the South Atlantic region*** and 17 (36%) were identified in the West South Central region***.

 Influenza Virus Isolated

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Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 7 influenza viruses submitted by U.S. laboratories since September 29: five influenza B viruses, one influenza A (H3N2) virus, and one influenza A (H1N2) virus. The influenza B viruses, the A (H3N2) virus, and the hemagglutinin protein of the A (H1N2) virus were similar antigenically to 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 47, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.1%. This percentage is below the epidemic threshold of 7.4% for week 47.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 47, 1.3% of patient visits to U.S. sentinel providers were due to ILI. This percentage is less than the national baseline of 1.9%. On a regional level***, the percentage of visits for ILI ranged from 0.4% to 2.1%. 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 Louisiana and Texas, and sporadic in 18 states (Colorado, Florida, Georgia, Hawaii, Indiana, Kansas, Kentucky, Maine, Michigan, Missouri, Nebraska, Nevada, New Mexico, Pennsylvania, Tennessee, Utah, West Virginia, and Wyoming) and Washington, D.C. Twenty-seven states and New York City reported no influenza activity, and 3 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.

†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 December 2, 2002

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