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Weekly Report: Influenza Summary Update

Week ending October 11, 2003-Week 41

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The following information may be quoted:

Synopsis:

During week 41 (October 5 - 11, 2003)*, no specimens tested by U.S. World Health Organization (WHO) collaborating laboratories were positive for influenza. The proportion of patient visits to sentinel providers for influenza-like illness (ILI) overall was 1,6 %, which is less than the national baseline of 2,5 %. The proportion of deaths attributed to pneumonia and influenza was 6,3 %. One state health department (Texas) reported regional influenza activity, 3 states and New York City reported sporadic influenza activity, and 43 states and the District of Columbia reported no influenza activity.

Laboratory Surveillance*:

During week 41, WHO laboratories reported 502 specimens tested for influenza viruses, and none were positive. Data from the National Respiratory and Enteric Virus Surveillance System (NREVSS) laboratories for week 41 were not available at the time this report was written; therefore, numbers may change substantially next week.

Laboratories other than those participating as U.S WHO or NREVSS collaborating laboratories may submit influenza isolates to CDC for further testing. From all data sources, influenza A(H3N2) viruses were reported during August from Alaska, Connecticut, the District of Columbia, Hawaii, New Hampshire, New York, and Wisconsin, and an unsubtyped influenza A virus was reported from Louisiana. During September, influenza A(H3N2) viruses were identified in Alaska, Connecticut, Hawaii, and Texas and unsubtyped influenza A viruses were identified in Louisiana, Texas, and Washington. In addition to the 1 influenza A(H3N2) isolate reported for week 40 through the WHO/NREVSS collaborating laboratories system, other influenza A(H3N2) viruses collected during October in Texas have been submitted to CDC for testing.

 Influenza Virus Isolated

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Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 41, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6,3 %. This percentage is below the epidemic threshold of 6,8 % for week 41.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 41, 1,6 %** 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 0,4 % to 5,8 %. 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**:

Influenza activity was reported as regional in 1 state (Texas) and sporadic in 3 states (Colorado, Florida, and Louisiana) and New York City. Forty-three states and the District of Columbia reported no influenza activity, and 3 states 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 17, 2003

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