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Weekly Report: Influenza Summary Update Week ending February 10, 2007-Week 6
Synopsis:
During week 6 (February 4 - February 10, 2007)*, influenza activity continued to increase 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, 26.9% were positive. ILI data was above baseline for week 6. Nineteen states reported widespread influenza activity; 14 states reported regional influenza activity; 12 states and New York City reported local influenza activity; five states and the District of Columbia reported sporadic influenza activity; and two states did not report. The reporting of widespread or regional influenza activity increased from 28 states for week 5 to 33 states for week 6. The percent of deaths due to pneumonia and influenza remained below baseline level.
Laboratory Surveillance*:
During week 6, WHO and NREVSS laboratories reported 3,986 specimens tested for influenza viruses, 1,071 (26.9%) of which were positive: 76 influenza A (H1) viruses, 12 influenza A (H3) viruses, 793 influenza A viruses that were not subtyped, and 190 influenza B viruses.
Since October 1, 2006, WHO and NREVSS laboratories have tested a total of 91,873 specimens for influenza viruses and 8,321 (9.1%) were positive. Among the 8,321 influenza viruses, 6,943 (83.4%) were influenza A viruses and 1,378 (16.6%) were influenza B viruses. One thousand nine hundred eighteen (27.6%) of the 6,943 influenza A viruses have been subtyped: 1,692 (88.2%) were influenza A (H1) viruses and 226 (11.8%) were influenza A (H3) viruses. Among specimens tested for influenza during the most recent three weeks (January 21 February 10, 2007), on a regional basis, the percent of specimens testing positive for influenza were as follows:
<table border="1" cellpadding="0" cellspacing="0"> <tbody><tr> <td colspan="3" valign="top" width="638">
January 21 ? February 10, 2007 (specimens testing positive)
</td> </tr> <tr> <td valign="top" width="209">>20% positive
</td> <td valign="top" width="213">10-20% positive
</td> <td valign="top" width="217"><10% positive
</td> </tr> <tr> <td valign="top" width="209">East North Central (39.5%)
</td> <td valign="top" width="213">South Atlantic (15.9%)
</td> <td valign="top" width="217">New England (8.6%)
</td> </tr> <tr> <td valign="top" width="209">West North Central (20.8%)
</td> <td valign="top" width="213">Mountain (16.0%)
</td> <td valign="top" width="217">Mid Atlantic (8.6%)
</td> </tr> <tr> <td valign="top" width="209">East South Central (29.7%)
</td> <td valign="top" width="213">Pacific (11.4%)
</td> <td valign="top" width="217"></td> </tr> <tr> <td valign="top" width="209">West South Central (33.5%)
</td> <td valign="top" width="213"></td> <td valign="top" width="217"></td> </tr> </tbody></table> 
CDC has antigenically characterized 161 influenza viruses [99 influenza A (H1), seven influenza A (H3) viruses, and 55 influenza B viruses] collected by U.S. laboratories since October 1, 2006.
Influenza A (H1) [99]
Pneumonia and Influenza (P&I) Mortality Surveillance*: " Ninety-three (94%) of the 99 viruses characterized were similar to A/New Caledonia/20/99-like, which is the influenza A (H1) component of the 2006-07 influenza vaccine.
" Six (6%) of the 99 viruses showed somewhat reduced titers with antisera produced against A/New Caledonia/20/99.
Influenza A (H3) [7] " Six (6%) of the 99 viruses showed somewhat reduced titers with antisera produced against A/New Caledonia/20/99.
" Four (57%) of the seven viruses were characterized as A/Wisconsin/67/2005-like, which is the influenza A (H3) component of the 2006-07 influenza vaccine.
" Three (43%) of the seven viruses showed somewhat reduced titers with antisera produced against A/Wisconsin/67/2005.
Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) [55]" Three (43%) of the seven viruses showed somewhat reduced titers with antisera produced against A/Wisconsin/67/2005.
Victoria lineage [37]
" Thirty-seven (67%) of the 55 influenza B viruses characterized belong to the B/Victoria lineage of viruses.
" Eighteen (33%) of the 55 influenza B viruses characterized belong to the B/Yamagata lineage of viruses.
" Thirty-seven (67%) of the 55 influenza B viruses characterized belong to the B/Victoria lineage of viruses.
o Eighteen (49%) of these 37 viruses were similar to B/Ohio/01/2005, the B component of the 2006-07 influenza vaccine.
o Nineteen (51%) of these 37 viruses showed somewhat reduced titers with antisera produced against B/Ohio/01/2005.
Yamagata lineage [18]o Nineteen (51%) of these 37 viruses showed somewhat reduced titers with antisera produced against B/Ohio/01/2005.
" Eighteen (33%) of the 55 influenza B viruses characterized belong to the B/Yamagata lineage of viruses.
During week 6, 6.7% of all deaths were reported as due to pneumonia or influenza. This percentage is below the epidemic threshold of 7.9% for week 6.
Three influenza-associated pediatric deaths were reported during week 6. Since October 1, 2006, CDC has received 13 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> </sup>: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN).
During November 5, 2006 February 3, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate for children aged 0-4 years old in the NVSN was 0.96 per 10,000.
During October 1, 2006 February 3, 2007, the preliminary laboratory-confirmed influenza-associated hospitalization rate reported by the EIP for children 017 years old was 0.18 per 10,000. For children aged 0-4 years and 5-17 years, the rate was 0.47 per 10,000 and 0.06 per 10,000, respectively.
Influenza-like Illness Surveillance*:
During week 6, 3.8%*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is above the national baseline**** of 2.1%. The proportion of visits for influenza-like illness may have been influenced by changes in healthcare seeking patterns during the holiday season as has been seen in past seasons.
Eight out of nine surveillance regions reported ILI above their region-specific baseline and one surveillance region reported ILI at the region-specific baseline****:
<table border="1" cellpadding="0" cellspacing="0"> <tbody><tr> <td valign="top" width="209">
Region
</td> <td valign="top" width="213">Reported ILI (%)
</td> <td valign="top" width="217">Region-Specific Baseline (%)
</td> </tr> <tr> <td valign="top" width="209">New England
</td> <td valign="top" width="213">2.0
</td> <td valign="top" width="217">1.2
</td> </tr> <tr> <td valign="top" width="209">Mid Atlantic
</td> <td valign="top" width="213">2.6
</td> <td valign="top" width="217">2.6
</td> </tr> <tr> <td valign="top" width="209">East North Central
</td> <td valign="top" width="213">3.4
</td> <td valign="top" width="217">1.9
</td> </tr> <tr> <td valign="top" width="209">West North Central
</td> <td valign="top" width="213">2.5
</td> <td valign="top" width="217">1.5
</td> </tr> <tr> <td valign="top" width="209">South Atlantic
</td> <td valign="top" width="213">2.7
</td> <td valign="top" width="217">2.3
</td> </tr> <tr> <td valign="top" width="209">East South Central
</td> <td valign="top" width="213">3.3
</td> <td valign="top" width="217">2.4
</td> </tr> <tr> <td valign="top" width="209">West South Central
</td> <td valign="top" width="213">8.5
</td> <td valign="top" width="217">3.0
</td> </tr> <tr> <td valign="top" width="209">Mountain
</td> <td valign="top" width="213">3.3
</td> <td valign="top" width="217">1.7
</td> </tr> <tr> <td valign="top" width="209">Pacific
</td> <td valign="top" width="213">4.9
</td> <td valign="top" width="217">3.2
</td> </tr> </tbody></table> Influenza Activity as Assessed by State and Territorial Epidemiologists*:
*: During week 6, the following influenza activity<sup> </sup> was reported:
" Widespread activity was reported by 19 states (Arkansas, Delaware, Georgia, Idaho, Indiana, Iowa, Kansas, Kentucky, Massachusetts, Minnesota, Nebraska, New York, Oklahoma, Oregon, South Carolina, South Dakota, Tennessee, Texas, and Wisconsin).
" Regional activity was reported by 14 states (Alaska, Arizona, California, Connecticut, Illinois, Maine, Nevada, New Jersey, North Carolina, North Dakota, Pennsylvania, Utah, Virginia, and Washington).
" Local activity was reported by New York City and 12 states (Alabama, Colorado, Florida, Hawaii, Louisiana, Maryland, Michigan, Missouri, Montana, New Mexico, West Virginia, and Wyoming).
" Sporadic activity was reported by the District of Columbia and five states (Mississippi, New Hampshire, Ohio, Rhode Island, and Vermont).
--------------------------------------------------------------------------------" Regional activity was reported by 14 states (Alaska, Arizona, California, Connecticut, Illinois, Maine, Nevada, New Jersey, North Carolina, North Dakota, Pennsylvania, Utah, Virginia, and Washington).
" Local activity was reported by New York City and 12 states (Alabama, Colorado, Florida, Hawaii, Louisiana, Maryland, Michigan, Missouri, Montana, New Mexico, West Virginia, and Wyoming).
" Sporadic activity was reported by the District of Columbia and five states (Mississippi, New Hampshire, Ohio, Rhode Island, and Vermont).
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<!-- InstanceEndEditable --> <!-- InstanceBeginEditable name="date" --> Report prepared February 8, 2007<!-- InstanceEndEditable -->
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