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Weekly Report: Influenza Summary Update
Week ending January 4, 2003-Week 1
Error processing SSI fileThe following information may be quoted:
Synopsis:
During week 1 (December 29, 2002 – January 4, 2003)*, 25
(2.2%) of the specimens tested by World Health Organization
(WHO) and National Respiratory and Enteric Virus Surveillance
System (NREVSS) laboratories were positive for influenza.
The proportion of patient visits to sentinel providers for
influenza-like illness (ILI) overall was 2.0%, which is greater
than the national baseline of 1.9%. The proportion of deaths
attributed to pneumonia and influenza was 6.8%. Seven state
and territorial health departments reported regional influenza
activity, 31 reported sporadic activity, and 11 reported
no influenza activity**.
Laboratory Surveillance*:
During week 1, WHO and NREVSS
laboratories reported 1,147 specimens tested for influenza
viruses, of which 25 (2.2%) were positive. Three influenza
A (H1)† virus, one influenza A (H3N2) virus, eight unsubtyped
influenza A viruses, and 13 influenza B viruses were identified.
During the past 3 weeks (weeks 51-1), 13.1% of the specimens
tested for influenza in the West South Central region***
were positive. Between 0.4% and 5.0% of specimens tested
for influenza were positive during the past 3 weeks in the
East North Central, Mid-Atlantic, Mountain, New England,
Pacific, South Atlantic, and West North Central regions.
Since September 29, WHO and NREVSS laboratories have tested
a total of 23,976 specimens for influenza viruses and 321
(1.3%) were positive. Of the 321 viruses identified, 90 (28%)
were influenza A viruses and 231 (72%) were influenza B viruses.
Twenty-four (27%) of the 90 influenza A viruses have been
subtyped; 18 (75%) were influenza A (H1)† viruses and 6 (25%)
were influenza A (H3N2) viruses. One hundred thirty-three
(58%) of the 231 influenza B viruses were identified in Texas.
Twenty-five states have reported laboratory-confirmed influenza.
Influenza A and influenza B viruses have been identified
in Arizona, California, Indiana, Louisiana, Missouri, Nebraska,
New York, North Carolina, South Carolina, Texas, and Virginia.
Florida, Hawaii, Massachusetts, Minnesota, New Jersey, Oregon,
South Dakota, Washington, and Wisconsin have reported only
influenza A viruses, and Arkansas, Kansas, Nevada, New Hampshire, and Oklahoma
have reported only influenza B viruses. Influenza A viruses were reported more
frequently than influenza B viruses (range 61% - 89%) in the East North Central,
Mid-Atlantic, New England, Pacific, and South Atlantic regions, and influenza
B viruses were reported more frequently than influenza A viruses (range 80%
- 88%) in the Mountain, West North Central, and West South Central regions.
The East South Central region has not reported any influenza viruses.
Antigenic Characterization of Viral Isolates:
CDC has antigenically characterized 42 influenza viruses submitted by U.S. laboratories since September 29: twenty-six influenza B viruses, four influenza A (H3N2) viruses, and 12 influenza A (H1)† viruses. Eleven of the influenza A (H1) viruses had the N1 neuraminidase and one had the N2 neuraminidase. The influenza B viruses, the A (H3N2) viruses, and the hemagglutinin proteins of the A (H1N1) and A (H1N2) viruses were similar antigenically to those of the corresponding vaccine strains B/Hong Kong/330/01, A/Panama/2007/99 (H3N2), and A/New Caledonia/20/99 (H1N1), respectively.
Click here for more information about influenza A (H1N2) viruses
Pneumonia and Influenza (P&I) Mortality Surveillance:
During
week 1, the percentage of all deaths due to pneumonia and
influenza as reported by the vital statistics offices
of 122 U.S. cities was 6.8%. This percentage is below the
epidemic threshold of 8.0% for week 1.
Influenza-like Illness Surveillance *:
During week 1, 2.0% of patient visits to U.S. sentinel providers were due to ILI. This percentage is greater than the national baseline of 1.9%. On a regional level***, the percentage of visits for ILI ranged from 0.6% to 4.1%. Due to wide variability in regional level data, it is not appropriate to apply the national baseline to regional level data.
Influenza Activity as Assessed by State and Territorial Epidemiologists**:
Influenza activity was reported as regional in 7 states (Arkansas, Kansas, New York, Oklahoma, Tennessee, Texas, and Virginia) and New York City. Thirty-one states and Washington D.C. reported sporadic activity, 11 states reported no influenza activity, and 1 state did not report.
* Reporting is incomplete for this week. Numbers may change
as more reports are received.
** Influenza activity is defined as influenza-like illness and/or culture-confirmed
influenza.
†Includes both the A (H1N1) and A (H1N2) influenza virus subtypes. The influenza
A (H1N2) strain appears to have resulted from the reassortment of the genes of
currently circulating influenza A (H1N1) and A (H3N2) subtypes. Because the hemagglutinin
proteins of the A (H1N2) viruses are similar to those of the currently circulating
A (H1N1) viruses and the neuraminidase proteins are similar to those of the currently
circulating A (H3N2) viruses, the 2002-03 influenza vaccine should provide protection
against A (H1N2) viruses.
*** 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)
Report prepared January 9, 2003
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