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 29, 2003-Week 13

Error processing SSI file

The following information may be quoted:

Synopsis

During week 13 (March 23-29, 2003)*, 94 (6.4%) 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 1.2%, which is below the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 7.6%. Nineteen state and territorial health departments reported regional influenza activity, 28 reported sporadic activity, and 2 reported no influenza activity**.

Laboratory Surveillance*:

During week 13, U.S. WHO and NREVSS laboratories reported 1,465 specimens tested for influenza viruses, of which 94 (6.4%) were positive. Eleven influenza A (H1)† viruses, three influenza A (H3N2) viruses, 61 unsubtyped influenza A viruses, and 19 influenza B viruses were identified. During the past 3 weeks (weeks 11-13), 27.4% of the specimens tested for influenza in the New England region*** were positive. Between 14.2% and 19.8% of specimens tested for influenza during the past 3 weeks in the West North Central, Mountain, and East North Central regions were positive, and between 5.3% and 10.7% of the specimens tested for influenza during the past 3 weeks in the West South Central, East South Central, Pacific, and South Atlantic regions were positive. In the Mid-Atlantic region less than 5% of specimens tested for influenza during the past 3 weeks were positive.

Since September 29, WHO and NREVSS laboratories have tested a total of 74,790 specimens for influenza viruses and 8,791 (11.8%) were positive. Of the 8,791 viruses identified, 4,513 (51%) were influenza A viruses and 4,278 (49%) were influenza B viruses. Two thousand one hundred and eighty-nine (49%) of the 4,513 influenza A viruses have been subtyped; 1,661 (76%) were influenza A (H1)† viruses and 528 (24%) were influenza A (H3N2) viruses. Influenza A viruses were reported more frequently than influenza B viruses (range 56% - 88%) 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 59% - 83%) in the West South Central, South Atlantic, West North Central, and East South Central regions. However, during the past 3 weeks (weeks 11-13), influenza A activity has increased to the point that during those weeks, influenza A viruses were reported more frequently than influenza B viruses in all nine surveillance regions.

 Influenza Virus Isolated

View Chart Data

Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 425 influenza viruses submitted by U.S. laboratories since September 29: one hundred and seventy-four influenza A (H1)† viruses, 63 influenza A (H3N2) viruses, and 188 influenza B viruses. Seventy-six of the influenza A (H1) viruses had the N1 neuraminidase, 27 had the N2 neuraminidase, and the neuraminidase typing for 71 H1 viruses is pending. The hemagglutinin proteins of all 174 influenza A (H1) viruses were similar antigenically to the hemagglutinin of the vaccine strain A/New Caledonia/20/99 (H1N1). Of the 63 influenza A (H3N2) isolates that have been characterized, 56 (89%) were similar to A/Panama/2007/99, the H3N2 component of the 2002-03 influenza vaccine, and 7 (11%) showed reduced titers to ferret antisera produced against A/Panama/2007/99. Of the 188 influenza B viruses that have been characterized, 187 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.

Composition of the 2003-04 Influenza Vaccine:

The Food and Drug Administration's Vaccine and Related Biological Products Advisory Committee recommended that the 2003-04 trivalent influenza vaccine for the United States contain A/New Caledonia/20/99-like (H1N1), A/Moscow/10/99-like (H3N2), and B/Hong Kong/330/2001-like viruses. All 3 components (H1N1, H3N2, and B) are the same as those for the 2002-03 season vaccine. This recommendation was based on antigenic analyses of recently isolated influenza viruses, epidemiologic data, and post-vaccination serologic studies in humans.

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

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 13, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 7.6%. This percentage is below the epidemic threshold of 8.1% for week 13.



Pneumonia And Influenza Mortality

View Full Screen

Influenza-like Illness Surveillance *:

During week 13, 1.2% of patient visits to U.S. sentinel providers were due to ILI. This percentage is below the national baseline of 1.9%. On a regional level***, the percentage of visits for ILI ranged from 0.2% to 3.1%. 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

View Chart Data

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

Influenza activity was reported as regional in 19 states (Alaska, Arizona, California, Colorado, Idaho, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, North Dakota, Ohio, Oregon, South Carolina, South Dakota, Tennessee, Utah, and Wisconsin). Twenty-eight states, New York City, and Washington, D.C. reported sporadic activity, and 2 states reported no influenza activity. One 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 April 3, 2003

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