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Weekly Report: Influenza Summary Update

Week ending October 23, 2004-Week 42

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The following information may be quoted:

Synopsis:

During week 42 (October 17 - October 23, 2004)*, influenza activity was low in the United States. Seven (0.7%) 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) was below baseline. The proportion of deaths attributed to pneumonia and influenza was 7.0%, which is slightly above the epidemic threshold of 6.8% for week 42. It is not unusual for the proportion of deaths to be above the epidemic threshold for a single week. Seventeen states, New York City, and Puerto Rico reported sporadic influenza activity, and 32 states and the District of Columbia reported no influenza activity.

Laboratory Surveillance*:

During week 42, WHO and NREVSS laboratories reported testing 1,009 specimens for influenza viruses, of which 7 (0.7%) were positive. Of these, 2 were influenza A (H3N2) viruses, 3 were influenza A viruses that were not subtyped, and 2 were influenza B viruses.

Since October 3, WHO and NREVSS laboratories have tested a total of 3,148 specimens for influenza viruses and 19 (0.6%) were positive. Among the 19 influenza viruses, 15 (78.9%) were influenza A viruses and 4 (21.1%) were influenza B viruses. Ten (66.7%) of the 15 influenza A viruses have been subtyped and all were influenza A (H3N2) viruses. Ten states from 7 of the 9 surveillance regions** have reported laboratory-confirmed influenza this season.

INFLUENZA Virus Isolated


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Antigenic Characterization:

Since October 1, 2004, CDC has antigenically characterized 1 influenza virus collected by U.S. laboratories. The influenza A (H3N2) virus was 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 42, 7.0% 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 slightly above the epidemic threshold of 6.8% for week 42.

Pneumonia And Influenza Mortality

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Influenza-Associated Pediatric Mortality*:

As of week 42, 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 16, 2004, there were no laboratory-confirmed influenza-associated hospitalizations for children 0 - 4 years old. 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 42, 1.4%*** 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 0.6% to 3.8%. 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*:

Seventeen states (Alaska, California, Colorado, Connecticut, Florida, Idaho, Indiana, Michigan, Minnesota, Montana, Nevada, New York, North Dakota, Rhode Island, Tennessee, Texas, and Wisconsin), New York City, and Puerto Rico reported sporadic influenza activity. Thirty-two states and the District of Columbia reported no influenza activity, and 1 state 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: October 28, 2004

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