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Weekly Report: Influenza Summary Update

Week ending October 4, 2003-Week 40

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The following information may be quoted:

Synopsis:

During week 40 (September 28 – October 4, 2003)*, 1 (0.2%) specimen tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories was positive for influenza. The proportion of patient visits to sentinel providers for influenza-like illness (ILI) overall was 0.9%, which is less than the national baseline of 2.5%. The proportion of deaths attributed to pneumonia and influenza was 6.0%. One state and territorial health department reported local influenza activity, 2 reported sporadic influenza activity, and 40 states, the District of Columbia, and New York City reported no influenza activity.

Laboratory Surveillance*:

During week 40, WHO and NREVSS laboratories reported 530 specimens tested for influenza viruses. One influenza A(H3N2) isolate was identified in the West South Central region.

Influenza isolates were reported during all months from June through September. 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 Connecticut 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 B viruses were not reported during this period.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 40, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.0%. This percentage is below the epidemic threshold of 6.7% for week 40.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 40, 0.9%** 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 0.1% to 1.8%. Due to wide variability in regional level data, it is not appropriate to apply the national baseline to regional level data.

Influenza Activity as Assessed by State and Territorial Epidemiologists**:

Influenza activity was reported as local in 1 state (Texas) and sporadic in 2 states (Alaska, Florida). Forty states, the District of Columbia, and New York City reported no influenza activity, and 7 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 10, 2003

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