Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file

Weekly Report: Influenza Summary Update

Week ending March 8, 2003-Week 10

Error processing SSI file

The following information may be quoted:

Synopsis:

During week 10 (March 2-8, 2003)*, 167 (18.4%) of the specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories were positive for influenza. The proportion of patient visits to sentinel providers for influenza-like illness (ILI) overall was 2.0%, which is above the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 8.0%. Nine state and territorial health departments reported widespread influenza activity, 23 reported regional activity, and 14 reported sporadic influenza activity**.

Laboratory Surveillance*:

During week 10, U.S. WHO and NREVSS laboratories reported 908 specimens tested for influenza viruses, of which 167 (18.4%) were positive. Forty-nine influenza A (H1)† viruses, 6 influenza A (H3N2) viruses, 42 unsubtyped influenza A viruses, and 70 influenza B viruses were identified. During the past 3 weeks (weeks 8-10), 33.7% of the specimens tested for influenza in the East North Central region*** were positive. Between 25.1% and 30.4% of specimens tested for influenza during the past 3 weeks in the West South Central, South Atlantic, Mountain, and New England regions were positive, and between 10.3% and 15.6% of the specimens tested in the East South Central and West North Central regions were positive for influenza. In the Mid-Atlantic and Pacific regions, less than 10% of specimens tested for influenza during the past 3 weeks were positive.

Since September 29, WHO and NREVSS laboratories have tested a total of 59,731 specimens for influenza viruses and 6,433 (10.8%) were positive. Of the 6,433 viruses identified, 2,916 (45%) were influenza A viruses and 3,517 (55%) were influenza B viruses. However, during the past 3 weeks (weeks 8-10) influenza A viruses have been reported more frequently (57%) than influenza B viruses. One thousand three hundred and twenty-nine (46%) of the 2,916 influenza A viruses have been subtyped; 1,089 (82%) were influenza A (H1)† viruses and 240 (18%) were influenza A (H3N2) viruses. One thousand four hundred and seventy-one (42%) of the 3,517 influenza B viruses were identified in Texas and Missouri. Laboratory-confirmed influenza has been reported in all 50 states. Influenza A viruses were reported more frequently than influenza B viruses (range 52% - 90%) in the New England, East North Central, Mountain, Pacific, and Mid-Atlantic regions, and influenza B viruses were reported more frequently than influenza A viruses (range 61% - 87%) in the West South Central, South Atlantic, West North Central, and East South Central regions. However, during the past 3 weeks (weeks 8-10), influenza A activity in the West South Central region has increased to the point that during those weeks, influenza A viruses were reported more frequently (71%) than influenza B viruses.

 Influenza Virus Isolated

View Chart Data

Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 266 influenza viruses submitted by U.S. laboratories since September 29: sixty-five influenza A (H1)† viruses, 54 influenza A (H3N2) viruses, and 147 influenza B viruses. Forty-five of the influenza A (H1) viruses had the N1 neuraminidase and 20 had the N2 neuraminidase. The hemagglutinin proteins of all 65 influenza A (H1) viruses were similar antigenically to the hemagglutinin of the vaccine strain A/New Caledonia/20/99 (H1N1). Of the 54 influenza A (H3N2) isolates that have been characterized, 47 (87%) were similar to A/Panama/2007/99, the H3N2 component of the 2002-03 influenza vaccine, and 7 (13%) showed reduced titers to ferret antisera produced against A/Panama/2007/99. Of the 147 influenza B viruses that have been characterized, 146 belonged to the B/Victoria lineage and were similar antigenically to the vaccine strain B/Hong Kong/330/01 and one belonged to the B/Yamagata lineage and was similar to B/Shizuoka/15/01, a B/Sichuan/379/99-like virus.

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

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 10, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 8.0%. This percentage is below the epidemic threshold of 8.3% for week 10.

Pneumonia And Influenza Mortality

View Full Screen

Influenza-like Illness Surveillance *:

During week 10, 2.0% of patient visits to U.S. sentinel providers were due to ILI. This percentage is above the national baseline of 1.9%. On a regional level***, the percentage of visits for ILI ranged from 0.9% to 4.7%. 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

View Chart Data

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

Influenza activity was reported as widespread in nine states (Alaska, Colorado, Michigan, Minnesota, Ohio, Rhode Island, Tennessee, Utah, and Wisconsin). Twenty-three states reported regional activity, and 14 states and New York City reported sporadic influenza activity. Four states and Washington, D.C. 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 March 13, 2003

Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file