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Weekly Report: Influenza Summary Update

Week ending November 2, 2002-Week 44

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The following information may be quoted:

Synopsis:

During week 44 (October 27-November 2, 2002)*, four 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 1.2%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.7%. One state and territorial health department reported regional influenza activity, 14 reported sporadic activity and 34 reported no influenza activity**.

Laboratory Surveillance*:

During week 44, WHO and NREVSS laboratories reported 884 specimens tested for influenza viruses of which 4 (0.5%) were positive. Two were unsubtyped influenza A viruses and 2 were influenza B viruses.

Since September 29, WHO and NREVSS laboratories have tested a total of 5,355 specimens for influenza viruses and 10 (0.2%) were positive. Of the 10 isolates identified, 7 were influenza A viruses and 3 were influenza B viruses. Four of the 10 influenza A isolates have been subtyped and all were influenza A (H1†) viruses. Influenza A isolates have been identified in Florida, Louisiana, New York, North Carolina, and South Carolina. Influenza B isolates have been identified in New York and South Carolina.

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Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized one influenza A (H1N2) virus collected from U.S. laboratories since September 29. This virus was isolated from a patient specimen collected in North Carolina in October. The hemagglutinin protein of this virus is antigenically similar to the hemagglutinin protein of the vaccine strain A/New Caledonia/20/99 (H1N1) and the neuraminidase protein is similar to the neuraminidase protein of the vaccine strain A/Panama/2007/99; therefore, the 2002-03 vaccine should provide protection against A (H1N2) viruses. During the 2001-02 season, influenza A (H1N2) viruses were isolated from several countries, including the U.S. These viruses resulted from gene reassortment among the circulating influenza A (H1N1) and A (H3N2) viruses. No information suggests that A (H1N2) viruses cause more severe illness that other influenza A viruses.

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

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 44, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.7%. This percentage is below the epidemic threshold of 7.1% for week 44.

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Influenza-like Illness Surveillance *:

During week 44, 1.2% 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 0.3% to 2.6%. Due to wide variability in regional level data, it is not appropriate to apply the national baseline to regional level data.

Influenza Activity as Assessed by State and Territorial Epidemiologists**:

Influenza activity was reported as regional in Louisiana and sporadic in 14 states (Alabama, Colorado, Florida, Georgia, Indiana, Kansas, Kentucky, Maine, Nebraska, Nevada, New Mexico, Tennessee, West Virginia, and Wyoming), and Washington, D.C. Thirty-four states and New York City reported no influenza activity, and one state did not report.

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* 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 circulatiing 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 November 7, 2002

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