Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file

Weekly Report: Influenza Summary Update

Week ending April 15, 2006-Week 15

Error processing SSI file

Synopsis:

During week 15 (April 9 – April 15, 2006)*, influenza activity continued to decrease in the United States. Two hundred twenty-one specimens (12.3%) 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 below the national baseline. The proportion of deaths attributed to pneumonia and influenza was below the baseline level. Five states reported widespread influenza activity; 5 states reported regional influenza activity; 16 states, New York City, and the District of Columbia reported local influenza activity; 23 states reported sporadic influenza activity; and one state reported no activity.

Laboratory Surveillance*:

During week 15, WHO and NREVSS laboratories reported 1,795 specimens tested for influenza viruses and 221 (12.3%) were positive. Of these, 25 were influenza A (H3N2) viruses, 18 were influenza A (H1N1) viruses, 60 were influenza A viruses that were not subtyped, and 118 were influenza B viruses.

Since October 2, 2005, WHO and NREVSS laboratories have tested a total of 123,245 specimens for influenza viruses and 15,789 (12.8%) were positive. Among the 15,789 influenza viruses, 13,291 (84.2%) were influenza A viruses and 2,498 (15.8%) were influenza B viruses. Five thousand four hundred thirty-two (40.9%) of the 13,291 influenza A viruses have been subtyped: 5,060 (93.2%) were influenza A (H3N2) viruses and 372 (6.8%) were influenza A (H1N1) viruses. During the past three weeks (weeks 13–15), the percentage of specimens testing positive for influenza has ranged from 27.8% in the South Atlantic region to 10.1% in the East South Central region**. During this period, the proportion of isolates identified as influenza B viruses continued to increase. During weeks 13-15, regions reporting the highest proportion of isolates as influenza B included the West North Central (65.9%), East North Central (62.4%), and Mountain (61.0%) regions. Other regions reporting more than 40.0% of recent isolates as influenza B include the Pacific, New England, and West South Central regions.

INFLUENZA Virus Isolated


View Chart Data | View Full Screen

Composition of the 2006-07 Influenza Vaccine:

WHO has recommended that the 2006-07 trivalent influenza vaccine for the Northern Hemisphere contain A/New Caledonia/20/99-like (H1N1), A/Wisconsin/67/2005-like (H3N2), and B/Malaysia/2506/2004-like viruses. The influenza A (H3N2) and the influenza B components have been changed from the 2005-06 season vaccine components. A/Wisconsin/67/2005 is an antigenic variant of the current vaccine strain A/California/07/2004. 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. The updating of the influenza B component to B/Ohio/1/2005 (which is antigenically equivalent to B/Malaysia/2506/2004) represents a change to the B/Victoria lineage. 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 624 influenza viruses [453 influenza A (H3N2), 43 influenza A (H1), and 128 influenza B viruses] collected by U.S. laboratories since October 1, 2005. Of the 453 influenza A (H3N2) viruses, 352 (77.7%) were characterized as A/California/07/2004-like, which is the influenza A (H3N2) component recommended for the 2005-06 influenza vaccine, and 101 (22.3%) viruses showed reduced titers with antisera produced against A/California/07/2004. Of the 101 low-reacting viruses, 75 were tested with antisera produced against A/Wisconsin/67/2005 (the H3N2 component selected for the 2006-07 vaccine), and 59 are A/Wisconsin-like. The hemagglutinin proteins of 40 (93.0%) influenza A (H1) viruses were antigenically similar to the hemagglutinin of the vaccine strain A/New Caledonia/20/99, and 3 (7.0%) showed reduced titers with antisera produced against A/New Caledonia/20/99. Forty (31.3%) of the influenza B viruses that have been characterized belong to the B/Yamagata lineage. Five were similar to B/Shanghai/361/2002, the recommended influenza B component for the 2005-06 influenza vaccine, 34 were characterized as B/Florida/07/2004-like, and 1 showed reduced titers with antisera produced against both B/Shanghai/361/2002 and B/Florida/07/2004. B/Florida/07/2004 is a minor antigenic variant of B/Shanghai/361/2002. Eighty-eight (68.8%) influenza B viruses were identified as belonging to the B/Victoria lineage and all were similar to B/Ohio/1/2005, the influenza B component selected for the 2006-07 vaccine.

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

During week 15, 7.3% 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 7.9% for week 15.

Pneumonia And Influenza Mortality

View Full Screen

Influenza-Associated Pediatric Mortality*:

During October 2, 2005 – April 15, 2006, CDC received reports of 24 influenza-associated pediatric deaths, 22 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†: Emerging Infections Program (EIP) and New Vaccine Surveillance Network (NVSN). During October 1, 2005 – April 1, 2006, the preliminary influenza-associated hospitalization rate reported by EIP for children aged 0-17 years was 0.98 per 10,000. For children aged 0-4 years and 5-17 years, the rate was 2.31 per 10,000 and 0.31 per 10,000, respectively. During October 30, 2005 – April 1, 2006, the preliminary laboratory-confirmed influenza-associated hospitalization rate for children aged 0-4 years in NVSN was 4.0 per 10,000. EIP and NVSN hospitalization rate estimates are preliminary and may change as data continue to be collected.

EIP Influenza Laboratory-Confirmed Cumulative Hospitalization Rates for Children Aged 0-4 and 5-17 years, 2005-06 and Previous 2 Seasons
View Full Screen
NVSN laboratory-confirmed influenza-associated hospitalizations for children 0-4 years old
View Full Screen

Influenza-like Illness Surveillance*:

During week 15, 1.5%*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is below the national baseline of 2.2%. The percentage of visits for ILI ranged from 1.0% in the West North Central region to 2.8% 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.

Bar Chart for Influenza-like Illness
View Chart Data | View Full Screen

Influenza Activity as Assessed by State and Territorial Epidemiologists*:

During week 15, 5 states (Connecticut, Delaware, Indiana, New York, and Rhode Island) reported widespread influenza activity. Five states (Kentucky, Maine, Minnesota, Virginia, and Wisconsin) reported regional influenza activity. Sixteen states (Florida, Georgia, Hawaii, Maryland, Michigan, New Hampshire, North Carolina, North Dakota, Ohio, Pennsylvania, South Carolina, South Dakota, Tennessee, Vermont, Washington, and West Virginia), New York City, and the District of Columbia reported local influenza activity. Twenty-three states (Alaska, Arizona, Arkansas, California, Colorado, Idaho, Illinois, Iowa, Kansas, Louisiana, Massachusetts, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, Oklahoma, Oregon, Texas, Utah, and Wyoming) reported sporadic influenza activity. Alabama reported no activity.

U. S. map for Weekly Influenza Activity
View Full Screen

--------------------------------------------------------------------------------

 

Foot notes

Report prepared April 21, 2006

Error processing SSI file
Error processing SSI file
Error processing SSI file
Error processing SSI file