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Weekly Report: Influenza Summary Update

Week ending October 16, 2004-Week 41

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The following information may be quoted:

Synopsis:

During week 41 (October 10 - October 16, 2004)*, influenza activity occurred at a low level in the United States. Two (0.3%) 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 levels. Nine states and New York City reported sporadic influenza activity, and 40 states and the District of Columbia reported no influenza activity.

Laboratory Surveillance*:

During week 41, WHO and NREVSS laboratories reported 652 specimens tested for influenza viruses, and 2 (0.3%) were positive. The 2 influenza viruses identified were influenza A (H3N2) viruses and were identified in the West South Central and Pacific regions.**

INFLUENZA Virus Isolated

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Antigenic Characterization:

CDC has antigenically characterized 1 influenza virus collected by U.S. laboratories since October 1, 2004. 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 41, 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 6.8% for week 41.

Pneumonia And Influenza Mortality

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Influenza-Associated Pediatric Mortality*:

As of week 41, no cases of influenza-associated pediatric deaths have been reported to CDC.

Influenza-Associated Pediatric Hospitalizations*:

The New Vaccine Surveillance Network (NVSN) provides estimates of hospitalization rates for children less than 5 years old in 3 sites. NVSN estimated rates of hospitalization for laboratory-confirmed influenza will be reported every 2 weeks, beginning October 29, 2004.

In addition, 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 41, 1.0%*** 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 1.5%. 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 sporadic in 9 states (California, Idaho, Indiana, Michigan, Montana, New Hampshire, New York, North Dakota, and Texas) and New York City. Forty 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 21, 2004

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