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Weekly Report: Influenza Summary Update

Week ending December 2, 2006-Week 48

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Synopsis:

During week 48 (November 26 December 2, 2006)*, a low level of influenza activity was reported in the United States. One hundred and six (4.3%) 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. Four states reported regional influenza activity; four states reported local influenza activity; 27 states, the District of Columbia, and New York City reported sporadic influenza activity; and 15 states reported no influenza activity.

Laboratory Surveillance*:

During week 48, WHO and NREVSS laboratories reported 2,441 specimens tested for influenza viruses, 106 (4.3%) of which were positive: fifteen influenza A (H1) viruses, one influenza A (H3), 61 influenza A viruses that were not subtyped, and 29 influenza B viruses.

Since October 1, 2006, WHO and NREVSS laboratories have tested a total of 22,677 specimens for influenza viruses and 724 (3.2%) were positive. Among the 724 influenza viruses, 568 (78.5%) were influenza A viruses and 156 (21.5%) were influenza B viruses. One hundred forty-four (25.4%) of the 568 influenza A viruses have been subtyped: 135 (93.8%) were influenza A (H1) viruses and 9 (6.2%) were influenza A (H3) viruses. Thirty-six states have reported positive laboratory influenza tests, but of the 724 influenza positive tests reported this season, 398 (55.0%) have been reported from Florida.

INFLUENZA Virus Isolated

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Antigenic Characterization:

CDC has antigenically characterized 27 influenza viruses [10 influenza A (H1) and 17 influenza B viruses] collected by U.S. laboratories since October 1, 2006.

Influenza A (H1)[10]
Eight of the 10 viruses were characterized as A/New Caledonia/20/99-like, which is the influenza A (H1) component of the 2006-07 influenza vaccine.
Two of the 10 viruses showed somewhat reduced titers with antisera produced against A/New Caledonia/20/99.
Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages)[17]
Victoria lineage [6]
Six (35.3%) of the 17 influenza B viruses characterized belong to the B/Victoria lineage of viruses.
o Three of these 6 viruses were similar to B/Ohio/01/2005, the B component of the 2006-07 influenza vaccine.
o Three of these 6 viruses showed somewhat reduced titers with antisera produced against B/Ohio/01/2005.
Yamagata lineage [11]
Eleven (64.7%) of the 17 influenza B viruses characterized belong to the B/Yamagata lineage of viruses.
It is too early in the influenza season to determine which influenza viruses will predominate or how well the vaccine and circulating strains will match.

Pneumonia and Influenza (P&I) Mortality Surveillance*:

During week 48, 6.34% of all deaths were reported as due to pneumonia or influenza. This percentage is below the epidemic threshold of 7.08% for week 48.

Pneumonia And Influenza Mortality

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Influenza-Associated Pediatric Mortality*:

No influenza-associated pediatric deaths were reported for week 48 and no deaths have been reported for the 2006-07 influenza season.

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). No influenza-associated pediatric hospitalizations have been reported from either network this season.

Influenza-like Illness Surveillance*:

During week 48, 1.7%*** 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 0.8% to 3.3%. Two regions reported ILI above their region-specific baseline****: the East South Central region reported 2.6% compared to its baseline of 2.4% and the West South Central region reported 3.3% compared to its baseline of 3.0%.

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

During week 48, the following influenza activity was reported:
Regional activity was reported by four states (Alabama, Florida, Georgia, and Mississippi).
Local activity was reported by four states (Connecticut, Louisiana, South Carolina, and Tennessee).
Sporadic activity was reported by the District of Columbia, New York City, and 27 states (Alaska, Arizona, Arkansas, California, Delaware, Hawaii, Idaho, Illinois, Indiana, Iowa, Kentucky, Maryland, Massachusetts, Michigan, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Texas, Utah, Virginia, West Virginia, Wisconsin, and Wyoming).
No influenza activity was reported by 15 states (Colorado, Kansas, Maine, Minnesota, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, Rhode Island, South Dakota, Vermont, and Washington).

U. S. map for Weekly Influenza Activity
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Foot notes

Report prepared December 8, 2006

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