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Weekly Report: Influenza Summary Update
Week ending February 24, 2007-Week 8
Error processing SSI fileSynopsis:
During week 8 (February 18 - February 24, 2007)*, influenza activity remained elevated in the United States. Among specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories for influenza, 23.8% were positive. ILI data was above baseline for the tenth week this season. Twenty-five states reported widespread influenza activity; 19 states and New York City reported regional influenza activity; three states and the District of Columbia reported local influenza activity; and three states reported sporadic influenza activity. The reporting of widespread or regional influenza activity increased from 38 states for week 7 to 44 states for week 8. The percent of deaths due to pneumonia and influenza remained below baseline level.
Laboratory Surveillance*:
During week 8, WHO and NREVSS laboratories reported 4,383 specimens tested for influenza viruses, 1,044 (24.8%) of which were positive: 97 influenza A (H1) viruses, 25 influenza A (H3) viruses, 727 influenza A viruses that were not subtyped, and 195 influenza B viruses.
Since October 1, 2006, WHO and NREVSS laboratories have tested a total of 109,790 specimens for influenza viruses and 13,003 (11.8%) were positive. Among the 13,003 influenza viruses, 10,929 (84.0%) were influenza A viruses and 2,074 (16.0%) were influenza B viruses. Three thousand forty-three (27.8%) of the 10,929 influenza A viruses have been subtyped: 2,595 (85.3%) were influenza A (H1) viruses and 448 (14.7%) were influenza A (H3) viruses. Among specimens tested for influenza during the most recent three weeks (February 4 ?February 24, 2007), on a regional basis, the percent of specimens testing positive for influenza were as follows:
February 4 – February 24, 2007 (specimens testing positive) |
|
>20% positive |
10-20% positive |
East North Central (42.1%) |
New England (16.8%) |
West North Central (28.8%) |
Mid Atlantic (13.5%) |
South Atlantic (20.8%) |
Mountain (18.0%) |
East South Central (38.9%) |
Pacific (19.7%) |
West South Central (37.3%) |
|
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Composition of the 2007-08 Influenza Vaccine:
WHO has recommended that the 2007-08 trivalent influenza vaccine for the Northern Hemisphere contain A/Solomon Islands/3/2006-like (H1N1), A/Wisconsin/67/2005-like (H3N2), and B/Malaysia/2506/2004-like viruses. The influenza A (H1N1) component has been changed from the 2006-07 season vaccine components. A/Solomon Islands/3/2006 is a recent antigenic variant of the current vaccine strain A/New Caledonia/20/99. The influenza A (H3N2) and influenza B components remain the same. B/Ohio/1/2005 is antigenically equivalent to B/Malaysia/2506/2004. This recommendation was based on antigenic analyses of recently isolated influenza viruses, epidemiologic data, and post-vaccination serologic studies in humans.
Antigenic Characterization:
CDC has antigenically characterized 246 influenza viruses [148 influenza A (H1), 20 influenza A (H3) viruses, and 78 influenza B viruses] collected by U.S. laboratories since October 1, 2006.
Influenza A (H1) [148]Influenza A (H3) [20]?One hundred forty-one (95%) of the 148 viruses characterized were similar to A/New Caledonia/20/99-like, which is the influenza A (H1) component of the 2006-07 influenza vaccine.
?Seven (5%) of the 141 viruses showed somewhat reduced titers with antisera produced against A/New Caledonia/20/99 and are similar to A/Solomon Islands/3/2006-like.
Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) [78]?Eleven (55%) of the 20 viruses were characterized as A/Wisconsin/67/2005-like, which is the influenza A (H3) component of the 2006-07 influenza vaccine.
?Nine (45%) of the 20 viruses showed somewhat reduced titers with antisera produced against A/Wisconsin/67/2005.
Victoria lineage [52]
?Fifty-two (67%) of the 78 influenza B viruses characterized belong to the B/Victoria lineage of viruses.Yamagata lineage [26]o Twenty-nine (56%) of these 52 viruses were similar to B/Ohio/01/2005, the B component of the 2006-07 influenza vaccine.
o Twenty-three (44%) of these 52 viruses showed somewhat reduced titers with antisera produced against B/Ohio/01/2005.
?Twenty-six (33%) of the 78 influenza B viruses characterized belong to the B/Yamagata lineage of viruses.
Pneumonia and Influenza (P&I) Mortality Surveillance*:
During week 8, 7.7% of all deaths were reported as due to pneumonia or influenza. This percentage is below the epidemic threshold of 7.9% for week 8.
Influenza-Associated Pediatric Mortality*:
Five influenza-associated pediatric deaths were reported during week 8. Since October 1, 2006, CDC has received 20 reports of influenza-associated pediatric deaths that occurred during the current season.
Influenza-Associated Pediatric Hospitalizations*:
Laboratory-confirmed influenza-associated pediatric hospitalizations are monitored in two population-based surveillance networks?/sup>: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN).
During November 5, 2006 ?February 17, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate for children aged 0-4 years old in the NVSN was 1.51 per 10,000.
During October 1, 2006 ?February 17, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate reported by the EIP for children 0?7 years old was 0.29 per 10,000. For children aged 0-4 years and 5-17 years, the rate was 0.74 per 10,000 and 0.11 per 10,000, respectively.
Influenza-like Illness Surveillance*:
During week 8, 3.5%*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is above the national baseline**** of 2.1%.
Seven out of nine surveillance regions reported ILI above their region-specific baseline**** and two surveillance regions reported ILI at their region-specific baseline:
Region |
Reported ILI (%) |
Region-Specific Baseline (%) |
New England |
2.0 |
1.2 |
Mid Atlantic |
2.6 |
2.6 |
East North Central |
3.6 |
1.9 |
West North Central |
2.6 |
1.5 |
South Atlantic |
2.3 |
2.3 |
East South Central |
3.9 |
2.4 |
West South Central |
7.9 |
3.0 |
Mountain |
3.2 |
1.7 |
Pacific |
3.7 |
3.2 |
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Chart Data
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Influenza Activity as Assessed by State and Territorial Epidemiologists*:
During week 8, the following influenza activity唵 was reported:
?Widespread activity was reported by 25 states (Alaska, Arkansas, Colorado, Connecticut, Delaware, Georgia, Idaho, Indiana, Iowa, Kansas, Kentucky, Nebraska, New Jersey, New York, North Carolina, North Dakota, Oklahoma, Oregon, South Dakota, Tennessee, Texas, Virginia, Washington, West Virginia, and Wisconsin).
?Regional activity was reported by New York City and 19 states (Arizona, California, Florida, Hawaii, Illinois, Louisiana, Maine, Massachusetts, Michigan, Minnesota, Montana, Nevada, New Hampshire, New Mexico, Ohio, Pennsylvania, South Carolina, Utah, and Wyoming).
?Local activity was reported by the District of Columbia and three states (Alabama, Mississippi, and Missouri).
?Sporadic activity was reported by three states (Maryland, Rhode Island, and Vermont).
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Report prepared March 2, 2007
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