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Weekly Report: Influenza Summary Update
Week ending February 4, 2006-Week 5
Error processing SSI fileSynopsis:
During week 5 (January 29 ?February 4, 2006)*, influenza activity continued approximately at the same level as recent weeks in the United States. Three hundred thirty-three specimens (13.9%) 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) was above the national baseline. The proportion of deaths attributed to pneumonia and influenza was below the baseline level. Nine states and New York City reported widespread influenza activity; 21 states reported regional influenza activity; 13 states and the District of Columbia reported local influenza activity; and 6 states and Puerto Rico reported sporadic influenza activity.
Laboratory Surveillance*:
During week 5, WHO and NREVSS laboratories reported 2,401 specimens tested for influenza viruses and 333 (13.9%) were positive. Of these, 96 were influenza A (H3N2) viruses, 2 were influenza A (H1N1) viruses, 211 were influenza A viruses that were not subtyped, and 24 were influenza B viruses.
Since October 2, 2005, WHO and NREVSS laboratories have tested a total of 61,861 specimens for influenza viruses and 4,466 (7.2%) were positive. Among the 4,466 influenza viruses, 4,312 (96.6%) were influenza A viruses and 154 (3.4%) were influenza B viruses. Two thousand and sixty-nine (48.0%) of the 4,312 influenza A viruses have been subtyped: 2,048 (99.0%) were influenza A (H3N2) viruses and 21 (1.0%) were influenza A (H1N1) viruses. All states have reported laboratory-confirmed influenza this season. During the past 3 weeks (weeks 3 ?5), the largest number of isolates have been reported from the Mountain and West South Central regions**. During this time, the percentage of specimens testing positive for influenza has ranged from 20.5% in the West South Central region to 3.7% in the East South Central region.
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Antigenic Characterization:
CDC has antigenically characterized 169 influenza viruses [149 influenza
A (H3N2), 9 influenza A (H1), and 11 influenza B viruses] collected by U.S.
laboratories since October 1, 2005. Of the 149 influenza A (H3N2) viruses,
123 were characterized as A/California/07/2004-like, which is the influenza
A (H3N2) component recommended for the 2005-06 influenza vaccine, and 26
showed reduced titers with antisera produced against A/California/07/2004.
The hemagglutinin proteins of 7 influenza A (H1) viruses were similar antigenically
to the hemagglutinin of the vaccine strain A/New Caledonia/20/99, and 2
showed reduced titers with antisera produced against A/New Caledonia/20/99.
Influenza B viruses currently circulating can be divided into two antigenically
distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses.
Eight of the influenza B viruses characterized belong to the B/Yamagata
lineage. One was similar to B/Shanghai/361/2002, the recommended influenza
B component for the 2005-06 influenza vaccine, and 7 were characterized
as B/Florida/07/2004-like. B/Florida/07/2004 is a minor antigenic variant
of B/Shanghai/361/2002. Three influenza B viruses were identified as belonging
to the B/Victoria lineage.
Pneumonia and Influenza (P&I) Mortality Surveillance*:
During week 5, 7.4% of all deaths reported by the vital statistics offices
of 122 U.S. cities were due to pneumonia or influenza. This percentage is
below the epidemic threshold of 8.2% for week 5.
Influenza-Associated Pediatric Mortality*:
One influenza-associated pediatric death was reported during week 5. Since October 2, 2005, CDC has received reports of 14 influenza-associated pediatric deaths, 12 of which occurred during the current influenza 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 October 1, 2005 ?January 21, 2006, the preliminary influenza-associated hospitalization rate reported by the EIP for children aged 0-17 years was 0.24 per 10,000. For children aged 0-4 years and 5-17 years, the rate was 0.66 per 10,000 and 0.04 per 10,000, respectively. During October 30, 2005 ?January 21, 2006, the preliminary laboratory-confirmed influenza-associated hospitalization rate for children aged 0-4 years in the NVSN was 0.21 per 10,000. EIP and NVSN hospitalization rate estimates are preliminary and may change as data continue to be collected.
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Influenza-like Illness Surveillance*:
During week 5, 2.3%*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is above the national baseline of 2.2%. The percentage of visits for ILI ranged from 1.4% in the West North Central region to 4.6% in the West South Central region**. Due to wide variability in regional level data, it is not appropriate to apply the national baseline to regional level data.
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Influenza Activity as Assessed by State and Territorial Epidemiologists*:
During week 5, 9 states (Colorado, Connecticut, Kansas, New York, Pennsylvania, South Carolina, Texas, Virginia, and Wyoming) and New York City reported widespread influenza activity. Twenty-one states (Alabama, Alaska, Arkansas, California, Florida, Georgia, Indiana, Iowa, Kentucky, Louisiana, Maryland, Massachusetts, Minnesota, Mississippi, Nebraska, North Carolina, Oklahoma, Oregon, Rhode Island, Tennessee, and Wisconsin) reported regional influenza activity. Thirteen states (Arizona, Idaho, Illinois, Maine, Michigan, Montana, Nevada, New Jersey, New Mexico, North Dakota, Ohio, South Dakota, and Washington) and the District of Columbia reported local influenza activity. Six states (Delaware, Hawaii, New Hampshire, Utah, Vermont, and West Virginia) and Puerto Rico reported sporadic influenza activity. One state did not report.
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Report prepared February 10, 2006
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