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Weekly Report: Influenza Summary Update
Week ending November 13, 2004-Week 45
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Synopsis:
During week 45 (November 7-13, 2004)*, influenza activity was low in the United States. Nine (0.7%) 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 values. One state reported widespread activity, and 1 state and New York City reported regional activity. Thirty-two states, District of Columbia, and Puerto Rico reported sporadic influenza activity and 16 states reported no influenza activity.
Laboratory Surveillance*:
During week 45, WHO and NREVSS laboratories reported testing 1,342 specimens for influenza viruses, of which 9 (0.7%) were positive. Of these, 1 was an influenza A (H3N2) virus, 3 were influenza A viruses that were not subtyped, and 5 were influenza B viruses.
Since October 3, WHO and NREVSS laboratories have tested a total of 9,514 specimens for influenza viruses and 84 (0.9%) were positive. Among the 84 influenza viruses, 59 (70.2%) were influenza A viruses and 25 (29.8%) were influenza B viruses. Twenty-eight (47.5%) of the 59 influenza A viruses have been subtyped and all were influenza A (H3N2) viruses. Twenty-three states from 8 of the 9 surveillance regions** have reported laboratory-confirmed influenza this season.
Antigenic Characterization:
CDC has antigenically characterized 11 influenza viruses collected by U.S. laboratories since October 1, 2004: nine influenza A (H3N2) viruses and 2 influenza B viruses. All of the influenza A (H3N2) isolates were characterized as A/Fujian/411/2002-like (H3N2), which is the influenza A (H3N2) component recommended for the 2004-05 influenza vaccine. Both influenza B viruses characterized were B/Shanghai/361/2002-like, which is the influenza B component recommended for the 2004-05 influenza vaccine.
Pneumonia and Influenza (P&I) Mortality Surveillance*:
During week 45, 6.7% of all deaths reported by the vital statistics offices of 122 U.S. cities were reported as due to pneumonia or influenza. This percentage is below the epidemic threshold of 7.1% for week 45.
Influenza-Associated Pediatric Mortality*:
As of week 45, no influenza-associated pediatric deaths have been reported to CDC.
Influenza-Associated Pediatric Hospitalizations:
The New Vaccine Surveillance Network consists of three sites in Cincinnati OH, Nashville TN, and Rochester NY. The sites conduct population-based surveillance for laboratory-confirmed influenza among children 0-4 years of age who are admitted to the hospital with fever or acute respiratory illnesses. During October 3-30, 2004, there were no laboratory-confirmed influenza-associated hospitalizations for children 0-4 years old. In years 2000-2003, the end-of-season hospitalization rate ranged from 2.8 to 12 per 10,000 children. Hospitalization rate estimates are preliminary and may change as data continue to be collected.
Emerging Infections Programs (EIP) in 9 sites are collecting data on laboratory-confirmed, influenza-associated hospitalizations among children less than 18 years of age. Hospitalization data from the EIP sites will be included as they become available.
Influenza-like Illness Surveillance*:
During week 45, 1.6%*** of patient visits to U.S. sentinel providers were due to ILI. This percentage is less than the national baseline of 2.5%. On a regional level**, the percentage of visits for ILI ranged from 0.7% to 2.3%. 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*:
Delaware reported widespread activity, and New York and New York City reported regional activity for the week 45. Thirty-two states (Alaska, Arizona, California, Colorado, Connecticut, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Kansas, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, North Carolina, North Dakota, Ohio, Rhode Island, Tennessee, Texas, Utah, Virginia, Washington, West Virginia, and Wisconsin), the District of Columbia, and Puerto Rico reported sporadic influenza activity. Sixteen states reported no influenza activity.
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* Reporting is incomplete for this week. Numbers may change as more reports are received.
** Surveillance Regions: New England (Connecticut, Maine, Massachusetts, New Hampshire, Vermont, Rhode Island); Mid-Atlantic (New Jersey, New York City, Pennsylvania, Upstate New York); East North Central (Illinois, Indiana, Michigan, Ohio, Wisconsin); West North Central (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota); South Atlantic (Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington, D.C., West Virginia); East South Central (Alabama, Kentucky, Mississippi, Tennessee); West South Central (Arkansas, Louisiana, Oklahoma, Texas); Mountain (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming); Pacific (Alaska, California, Hawaii, Oregon, Washington)
*** The national and regional percentage of patient visits for ILI is weighted on the basis of state population.
Report prepared: November 18, 2004
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