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Weekly Report: Influenza Summary Update

Week 42, ending October 21, 2006

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Synopsis:

During week 42 (October 15 - October 21, 2006)*, a low level of influenza activity was reported in the United States.  Three (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.  Two states reported local influenza activity; nine states and New York City reported sporadic influenza activity; and 39 states, and the District of Columbia reported no influenza activity.

Laboratory Surveillance*:

During week 42, WHO and NREVSS laboratories reported 1 164 specimens tested for influenza viruses, three of which were positive: one influenza A (H3) virus, one influenza A virus that was not subtyped, and one influenza B virus.

Since October 1, 2006, WHO and NREVSS laboratories have tested a total of 3 833 specimens for influenza viruses and 32 (0,8 %) were positive. Among the 32 influenza viruses, 24 (75 %) were influenza A viruses and 8 (25 %) were influenza B viruses.  Twenty-two (91,7 %) of the 24 influenza A viruses have been subtyped:  18 (81,8 %) were influenza A (H1) viruses and 4 (18,2 %) were influenza A (H3) viruses.   Ten states from six of the nine surveillance regions** have reported laboratory confirmed influenza this season.

INFLUENZA Virus Isolated


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Antigenic Characterization:

Since October 1, 2006, CDC has antigenically characterized 1 influenza virus collected by U.S. laboratories. The influenza A (H1) virus was characterized as A/New Caledonia/20/99 -like, which is the influenza A (H1) component recommended for the 2006-07 influenza vaccine.

Pneumonia and Influenza Mortality Surveillance:

During week 42, 5,86 % of all deaths were reported as due to pneumonia or influenza. This percentage is below the epidemic threshold of 6,46 % for week 42.

Pneumonia And Influenza Mortality

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Influenza-Associated Pediatric Mortality:

No influenza- associated pediatric deaths were reported for week 42.

Influenza-Associated Pediatric Hospitalizations

Laboratory-confirmed influenza-associated pediatric hospitalizations are monitored in two population-based surveillance networks: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN). EIP estimated rates of hospitalization for influenza will be reported every 2 weeks beginning October 27, 2006. NVSN estimated rates of hospitalization for influenza will be reported every 2 weeks, beginning December 2006.

Influenza-like Illness Surveillance*:

During week 42, 1,2 %*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is less than the national baseline**** of 2,1 %. On a regional level**, the percentage of visits for ILI ranged from 0,5 % to 1,9 % with no regions above their region-specific baseline****.

Bar Chart for Influenza-like Illness
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Influenza Activity as Assessed by State and Territorial Epidemiologists*:

During week 42, the following influenza activity was reported:

U. S. map for Weekly Influenza Activity
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Foot notes

Report prepared October 27, 2006 Error processing SSI file
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