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Weekly Report: Influenza Summary Update
Week ending December 8, 2001-Week 49
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Synopsis:
During week 49 (December 2-8, 2001)*, 11 of 943 respiratory specimens tested by WHO and NREVSS laboratories were positive for influenza. The overall proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 1.2%, which is less than the national baseline of 1.9%. The proportion of deaths attributed to pneumonia and influenza was 6.7%, which is below the epidemic threshold of 7.6% for week 49. One state and territorial health department reported widespread influenza activity, one reported regional activity, 33 reported sporadic activity, and 14 reported no influenza activity**.
Laboratory Surveillance*:
During week 49, WHO and NREVSS laboratories reported 943 specimens tested for influenza viruses. Two influenza A (H3N2) viruses, 6 unsubtyped influenza A viruses, and 3 influenza B viruses were identified.
Since September 30, WHO and NREVSS laboratories have tested a total of 12,282 specimens for influenza viruses and 172 (1.4%) were positive. Of the 172 isolates identified, 163 (95%) were influenza A viruses and 9 (5%) were influenza B viruses. One hundred and twelve (69%) of the 163 influenza A viruses identified have been subtyped; 111 were influenza A (H3N2) viruses and one was an influenza A (H1N1) virus. Twenty-two states have reported laboratory-confirmed influenza. Influenza A (H3N2) isolates were identified in Alaska, Arizona, Colorado, Florida, Hawaii, New York, North Carolina, North Dakota, Pennsylvania, South Carolina, Texas, Utah, and Wisconsin; the influenza A (H1N1) isolate was identified in Washington; and unsubtyped influenza A isolates were identified in Alabama, Alaska, Colorado, Hawaii, Kansas, Louisiana, Minnesota, New York, Oregon, Texas, Virginia, Washington, Wisconsin, and West Virginia. Influenza B isolates were identified in Hawaii, Louisiana, Michigan, Texas, and Virginia. Eighty-eight (51%) of the 172 influenza viruses isolated were identified in Alaska.
Antigenic Characterization:
CDC antigenically characterized 10 influenza viruses collected in September and 23 collected in October: 30 influenza A (H3N2) viruses, 2 influenza A (H1N1) viruses, and 1 influenza B virus. All viruses were similar to the vaccine strains A/Panama/2007/99 (H3N2), A/New Caledonia/ 20/99 (H1N1), and B/Sichuan/379/99, respectively.
Pneumonia and Influenza (P&I) Mortality Surveillance:
During week 49, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6.7%. This percentage is below the epidemic threshold of 7.6% for week 49.
Influenza-like Illness Surveillance *:
During week 49, 1.2% of patient visits to U.S. sentinel physicians were due to ILI. This is below the national baseline of 1.9%. On a regional level, the percentage of visits for ILI ranged from 0.8% to 3.9%.*** Due to wide variability in regional level data, it is not possible to calculate region-specific baselines and 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 widespread in Alaska and regional in Colorado. Thirty-three states and Washington, DC reported sporadic activity, and 14 states and New York City reported no influenza activity. One 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.
*** 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 December 13, 2001
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