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Weekly Report: Influenza Summary Update

Week ending December 27, 2003-Week 52

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The following information may be quoted:

Synopsis:

The number of states reporting widespread influenza activity decreased during week 52 (December 21 - 27, 2003). However, the percentage of outpatient visits for influenza-like illness (ILI) continued to increase (9.4%), and pneumonia and influenza (P & I) mortality (9.0%) exceeded the epidemic threshold for week 52 (7.9%). Nine hundred eighty-eight (28.1%) of 3,510 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. Forty-two state health departments, New York City, and the District of Columbia reported widespread influenza activity and 8 states reported regional activity. Availability of trivalent inactivated influenza vaccine is limited; additional doses of the vaccine previously purchased by CDC will be shipped to state and local public health agencies in January. The live, attenuated influenza vaccine continues to be available in both the private and public sectors.

Laboratory Surveillance*:

During week 52, WHO and NREVSS laboratories reported 3,510 specimens tested for influenza viruses, and 988 (28.1%) were positive. Of these, 148 were influenza A(H3N2) viruses, 836 were influenza A viruses that were not subtyped, and 4 were influenza B viruses.

Since September 28, WHO and NREVSS laboratories have tested a total of 50,743 specimens for influenza viruses and 14,942 (29.4%) were positive. Among the 14,942 influenza viruses, 14,847 (99.4%) were influenza A viruses and 95 (0.6%) were influenza B viruses. Three thousand five hundred seventy-seven (24.1%) of the 14,847 influenza A viruses have been subtyped; 3,576 (99.9%) were influenza A (H3N2) viruses and 1 (0.1%) was an A (H1) virus. All 50 states have reported laboratory-confirmed influenza this season.

Influenza Virus Isolated


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Antigenic Characterization:

CDC has antigenically characterized 361 influenza viruses collected by U.S. laboratories since October 1: two influenza A (H1) viruses, 357 influenza A (H3N2) viruses, and two 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 357 influenza A (H3N2) isolates that have been characterized, 91 (25.5%) were similar antigenically to the vaccine strain A/Panama/2007/99 (H3N2), and 266 (74.5%) were similar to the drift variant, A/Fujian/411/2002 (H3N2). Both influenza B viruses characterized were similar antigenically to B/Sichuan/379/99.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 52, 9.0% 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 7.9% for week 52.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 52, 9.4%** of patient visits to U.S. sentinel providers were due to ILI. This percentage is above the national baseline of 2.5%. The percentage of patient visits for ILI increased in 7 of the 9 surveillance regions. On a regional level***, the percentage of visits for ILI was highest in the East North Central region (11.4%), followed by the South Atlantic region (10.4%), the Mid-Atlantic and Pacific regions (10.1%), West South Central region (8.5%), Mountain region (7.6%), West North Central region (7.4%), New England region (6.7%), and East South Central region (5.8%). Due to wide variability in regional level data, it is not appropriate to apply the national baseline to regional level data. Some elevations in ILI may be due to fewer routine visits scheduled during holiday weeks.

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 42 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Wisconsin, and Wyoming), New York City, and the District of Columbia. Regional activity was reported by 8 states (Hawaii, Kansas, Kentucky, Louisiana, Nebraska, Oklahoma, Washington, and West Virginia).

U. S. map for Weekly Influenza Activity
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Vaccine Availability:

In the private sector, trivalent inactivated influenza vaccine is no longer available for sale by the manufacturers, although some vaccine may still be available through private wholesale/distribution companies. The live, attenuated influenza vaccine continues to be available for purchase from Wyeth Pharmaceuticals (Collegeville, Pennsylvania, telephone 800-358-7443).

In the public sector, the live, attenuated influenza vaccine is also available for immediate purchase through a CDC contract. Additional doses of trivalent inactivated influenza vaccine previously purchased through CDC contracts will be shipped to state and local public health agencies in early to mid-January.


* 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.

*** 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 2, 2004

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