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Weekly Report: Influenza Summary Update

Week ending January 17, 2004-Week 2

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The following information may be quoted:

Synopsis:

The number of states reporting widespread influenza activity continued to decrease during week 2 (January 11-17, 2004), with the majority of states reporting regional influenza activity. The percentage of specimens testing positive for influenza also decreased and the percentage of patient visits for influenza-like illness (ILI) declined again in all 9 surveillance regions. The national percentage of ILI (2.0%) declined below the national baseline of 2.5%. However, pneumonia and influenza mortality (10.3%) continued to exceed the epidemic threshold during week 2 (8.1%). One hundred twenty-three (8.0%) of 1,544 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. Five state health departments reported widespread influenza activity, 31 states and New York City reported regional activity, 8 states reported local activity, and 6 states, the District of Columbia, Guam, and Puerto Rico reported sporadic activity.

Laboratory Surveillance*:

During week 2, WHO and NREVSS laboratories reported 1,544 specimens tested for influenza viruses, and 123 (8.0%) were positive. Of these, 26 were influenza A(H3N2) viruses, 95 were influenza A viruses that were not subtyped, and 2 were influenza B viruses.

Since September 28, WHO and NREVSS laboratories have tested a total of 76,311 specimens for influenza viruses and 19,968 (26.2%) were positive. Among the 19,968 influenza viruses, 19,853 (99.4%) were influenza A viruses and 115 (0.6%) were influenza B viruses. Four thousand six hundred fifty-two (23.4%) of the 19,853 influenza A viruses have been subtyped; 4,651 (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 573 influenza viruses collected by U.S. laboratories since October 1: two influenza A (H1) viruses, 565 influenza A (H3N2) viruses, and six 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 565 influenza A (H3N2) isolates that have been characterized, 106 (18.8%) were similar antigenically to the vaccine strain A/Panama/2007/99 (H3N2), and 459 (81.2%) were similar to the drift variant, A/Fujian/411/2002 (H3N2). Five 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 2, 10.3% 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 2.

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 2.0%** during week 2, which is below the national baseline of 2.5%. The percentage of patient visits for ILI in all nine surveillance regions*** ranged from 2.5% in the Pacific region to 1.1% in the New England 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 five states (Delaware, Minnesota, New York, Pennsylvania, and Vermont). Regional activity was reported in 31 states (Colorado, Connecticut, Florida, Georgia, Hawaii, Idaho, Indiana, Iowa, Kentucky, Louisiana, Maine, Massachusetts, Michigan, Mississippi, Missouri, Montana, New Hampshire, New Jersey, North Carolina, North Dakota, Ohio, Oregon, Rhode Island, South Carolina, Tennessee, Texas, Utah, Virginia, West Virginia, Wisconsin, and Wyoming) and New York City. Local activity was reported in eight states (Alaska, Arizona, California, Illinois, Kansas, Maryland, Nebraska, and Washington). Sporadic activity was reported in six states (Alabama, Arkansas, Nevada, New Mexico, Oklahoma, and South Dakota), the District of Columbia, Guam, and Puerto Rico.

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 21, 2004

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