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Weekly Report: Influenza Summary Update

Week ending November 6, 2004-Week 44

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The following information may be quoted:

Synopsis:

During week 44 (October 31 - November 6, 2004)*, influenza activity was low in the United States. Six (0.6%) 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) and the proportion of deaths attributed to pneumonia and influenza were below baseline values. Twenty-eight states, New York City, and the District of Columbia reported sporadic influenza activity and 20 states reported no influenza activity.

Laboratory Surveillance*:

During week 44, WHO and NREVSS laboratories reported testing 958 specimens for influenza viruses, of which 6 (0.6%) were positive. Of these, 1 was an influenza A (H3N2) virus, 2 were influenza A viruses that were not subtyped, and 3 were influenza B viruses.

Since October 3, WHO and NREVSS laboratories have tested a total of 6,411 specimens for influenza viruses and 53 (0.8%) were positive. Among the 53 influenza viruses, 39 (73.6%) were influenza A viruses and 14 (26.4%) were influenza B viruses. Eighteen (46.2%) of the 39 influenza A viruses have been subtyped and all were influenza A (H3N2) viruses. Nineteen states from 8 of the 9 surveillance regions** have reported laboratory-confirmed influenza this season.

INFLUENZA Virus Isolated


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Antigenic Characterization:

CDC has antigenically characterized 3 influenza viruses collected by U.S. laboratories since October 1, 2004. All were influenza A (H3N2) viruses and were characterized as A/Fujian/411/2002-like, which is the influenza A (H3N2) component recommended for the 2004-05 influenza vaccine.

Pneumonia and Influenza (P&I) Mortality Surveillance*:

During week 44, 6.4% of all deaths reported by the vital statistics offices of 122 U.S. cities were reported as due to pneumonia or influenza. This percentage is below the epidemic threshold of 7.0% for week 44.

Pneumonia And Influenza Mortality

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Influenza-Associated Pediatric Mortality*:

As of week 44, no influenza-associated pediatric deaths have been reported to CDC.

Influenza-Associated Pediatric Hospitalizations:

The New Vaccine Surveillance Network consists of three sites in Cincinnati OH, Nashville TN, and Rochester NY. The sites conduct population-based surveillance for laboratory-confirmed influenza among children 0 - 4 years of age who are admitted to the hospital with fever or acute respiratory illnesses. During October 3 - October 30, 2004, there were no laboratory-confirmed influenza-associated hospitalizations for children 0 - 4 years old. In years 2000 - 2003, the end-of-season hospitalization rate ranged from 2.8 per 10,000 to 12 per 10,000 children. Hospitalization rate estimates are preliminary and may change as data continue to be collected.

Emerging Infections Programs (EIP) in 9 sites are collecting data on laboratory-confirmed, influenza-associated hospitalizations among children less than 18 years of age. Hospitalization data from the EIP sites will be included as they become available.

Influenza-like Illness Surveillance*:

During week 44, 1.2%*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is less than the national baseline of 2.5%. On a regional level**, the percentage of visits for ILI ranged from 0.9% to 2.2%. 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*:

Twenty-eight states (Alaska, Arizona, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Indiana, Kansas, Louisiana, Maryland, Massachusetts, Minnesota, Missouri, Nebraska, New York, North Carolina, North Dakota, Ohio, Rhode Island, Tennessee, Texas, Virginia, West Virginia, and Wisconsin), the District of Columbia, and New York City reported sporadic influenza activity. Twenty states reported no influenza activity and 2 states 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.

** 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)

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

Report prepared: November 11, 2004

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