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Weekly Report: Influenza Summary Update

Week ending January 10, 2004-Week 1

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The following information may be quoted:

Synopsis:

The number of states reporting widespread influenza activity continued to decrease during week 1 (January 4-10, 2004), the percentage of specimens testing positive for influenza also decreased, and the percentage of patient visits for influenza-like illness (ILI) declined in all 9 surveillance regions, with an overall national percentage of 2.8%. However, pneumonia and influenza (P & I) mortality (10.2%) continued to exceed the epidemic threshold during week 1 (8.1%). Three hundred nineteen (11.9%) of 2,670 specimens collected from throughout the United States and tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories were positive for influenza. Twenty state health departments and New York City reported widespread influenza activity, 24 states reported regional activity, 3 states reported local activity, 2 states, the District of Columbia, Guam, and Puerto Rico reported sporadic activity, and 1 state did not report.

Laboratory Surveillance*:

During week 1, WHO and NREVSS laboratories reported 2,670 specimens tested for influenza viruses, and 319 (11.9%) were positive. Of these, 52 were influenza A(H3N2) viruses, 261 were influenza A viruses that were not subtyped, and 6 were influenza B viruses.

Since September 28, WHO and NREVSS laboratories have tested a total of 69,052 specimens for influenza viruses and 18,535 (26.8%) were positive. Among the 18,535 influenza viruses, 18,422 (99.4%) were influenza A viruses and 113 (0.6%) were influenza B viruses. Four thousand four hundred eighteen (23.8%) of the 18,535 influenza A viruses have been subtyped; 4,417 (99.9%) were influenza A (H3N2) viruses and 1 (0.1%) was an A (H1) virus.

Influenza Virus Isolated


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Antigenic Characterization:

CDC has antigenically characterized 518 influenza viruses collected by U.S. laboratories since October 1: two influenza A (H1) viruses, 511 influenza A (H3N2) viruses, and five influenza B viruses. The hemagglutinin proteins of the influenza A (H1) viruses were similar antigenically to the hemagglutinin of the vaccine strain A/New Caledonia/20/99. Of the 511 influenza A (H3N2) isolates that have been characterized, 98 (19.2%) were similar antigenically to the vaccine strain A/Panama/2007/99 (H3N2), and 413 (80.8%) were similar to the drift variant, A/Fujian/411/2002 (H3N2). Four influenza B viruses characterized were similar antigenically to B/Sichuan/379/99 and 1 was similar antigenically to B/Hong Kong/330/2001.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 1, 10.2% of all deaths reported by the vital statistics offices of 122 U.S. cities were due to pneumonia and influenza. This percentage is above the epidemic threshold of 8.1% for week 1.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

The percentage of patient visits to approximately 1,000 U.S. sentinel providers nationwide for ILI decreased to 2.8%** during week 1, but remained above the national baseline of 2.5%. The percentage of patient visits for ILI continued to decrease in all nine surveillance regions***, ranging from 3.4% in the Pacific region to 1.9% in the Mountain and West North Central regions. 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 widespread in 20 states (California, Connecticut, Delaware, Georgia, Hawaii, Indiana, Iowa, Maryland, Minnesota, Mississippi, Montana, New York, North Carolina, Pennsylvania, South Carolina, Texas, Vermont, Virginia, West Virginia, and Wisconsin) and New York City. Regional activity was reported in 24 states (Alabama, Alaska, Arizona, Colorado, Florida, Idaho, Illinois, Kentucky, Louisiana, Massachusetts, Michigan, Missouri, Nebraska, New Hampshire, New Jersey, North Dakota, Ohio, Oregon, Rhode Island, South Dakota, Tennessee, Utah, Washington, and Wyoming). Local activity was reported in three states (Kansas, Nevada, and Oklahoma). Sporadic activity was reported in two states (Arkansas and New Mexico), the District of Columbia, Guam, and Puerto Rico. Maine did not report.

U. S. map for Weekly Influenza Activity
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* Reporting is incomplete for this week. Numbers may change as more reports are received.

** The national and regional percentage of patient visits for ILI is weighted on the basis of state population.

*** 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 14, 2004

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