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Weekly Report: Influenza Summary Update

Week ending October 25, 2003-Week 43

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The following information may be quoted:

Synopsis:

During week 43 (October 19 – 25, 2003)*, 48 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) overall was 1.8%, which is less than the national baseline of 2.5%. The proportion of deaths attributed to pneumonia and influenza was 6.1%. One state health department reported widespread influenza activity, 2 states reported local influenza activity, 14 states reported sporadic influenza activity, and 29 states and New York City reported no influenza activity.

Laboratory Surveillance*:

During week 43, WHO and NREVSS laboratories reported 707 specimens tested for influenza viruses, and 48 (6.8%) were positive. Thirty-two influenza A(H3N2) and 15 unsubtyped influenza A viruses and 1 influenza B virus were identified.

Since September 28, WHO and NREVSS laboratories have tested a total of 3,115 specimens for influenza viruses and 121 (3.9%) were positive. Of the 121 viruses identified, 119 (98%) were influenza A viruses and 2 (2%) were influenza B viruses. Forty-seven (39%) of the 119 influenza A viruses have been subtyped; all were influenza A (H3N2) viruses. One hundred ten (91%) of the 121 isolates were reported from the West South Central region**. Eleven states have reported laboratory-confirmed influenza during October. Influenza A viruses have been identified in Arizona, Arkansas, Colorado, Florida, Louisiana, New York, Oklahoma, Texas, and Washington. Influenza B viruses have been identified in Hawaii and North Dakota.

 Influenza Virus Isolated

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Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 43, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.1%. This percentage is below the epidemic threshold of 6.9% for week 43.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 43, 1.8%*** 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 0.7% to 6.6%. 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 1 state (Texas), local in 2 states (Alabama and Louisiana) and sporadic in 14 states (Arkansas, Colorado, Florida, Hawaii, Massachusetts, Missouri, Nebraska, New Mexico, North Dakota, North Carolina, Oklahoma, Oregon, Tennessee, and Utah). Twenty-nine states and New York City reported no influenza activity, and 4 states and the District of Columbia did not report.


Usmap for Weekly Influenza Activity


* 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 October 31, 2003

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