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Influenza Summary Update
(Week ending December 16, 2000-Week 50)
The following information may be quoted:
Synopsis: During week 50 (December 10-16, 2000)*, 59 of the specimens tested by WHO and NREVSS laboratories were positive for influenza type A virus and 12 were positive for influenza type B virus. The proportion of patient visits to sentinel physicians for influenza-like illness was within baseline levels of 0% to 3% in the United States overall and in 8 of 9 surveillance regions. The proportion of deaths attributed to pneumonia and influenza was 7.1%. This percentage is below the epidemic threshold for this time of year. One state and territorial health department reported widespread influenza activity**, 6 reported regional activity, 35 reported sporadic activity, and 7 reported no influenza activity.
U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) Collaborating Laboratory Reports*:
During week 50, WHO and NREVSS laboratories reported 1030 specimens tested for influenza viruses, of which 71 (7%) were positive. Twenty-six were influenza A(H1N1) viruses, 33 were unsubtyped influenza A viruses, and 12 were influenza B viruses.
Since October 1, WHO and NREVSS laboratories have tested a total of 14,010 specimens for influenza viruses, and 349 (2%) have yielded influenza virus isolates. Of the 349 isolates identified, 259 (74%) were influenza type A and 90 (26%) were influenza type B. Of the 259 influenza A viruses, 182 (70%) have been subtyped; 174 (96%) were A (H1N1) and 8 (4%) were A (H3N2). Three hundred and thirteen (90%) of the 349 U.S. isolates have been reported from the West South Central*** [208 (60%)], Pacific [60 (17%)], and South Atlantic [45 (13%)] regions. Influenza A(H1N1) viruses have predominated in the West South Central and South Atlantic regions. In the West South Central region, the majority [186 (89%)] of isolates reported were from Texas. In the Pacific region, influenza type B viruses accounted for 50 (83%) of the 60 isolates reported. Thirty-eight (76%) of the 50 influenza B viruses reported in the Pacific region were from Alaska.
Antigenic Characterization of Viral Isolates: CDC has antigenically characterized 33 influenza viruses received from U.S. laboratories since October 1: six influenza A(H3N2) viruses, 19 influenza A(H1N1) viruses, and eight influenza B viruses. These viruses were antigenically similar to vaccine strains A/Panama/2007/99 (H3N2), A/New Caledonia/20/99 (H1N1), and B/Beijing/184/93, respectively.
Pneumonia and Influenza (P&I) Mortality: During week 50, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 7.1%. This percentage is below the epidemic threshold of 8.2% for week 50.
Influenza Morbidity Reports from U.S. Sentinel Physicians *: During week 50, 2% of patient visits to U.S. sentinel physicians were due to influenza-like illness (ILI). The percentage of ILI was within baseline levels of 0% to 3% in 8 of 9 surveillance regions. Four percent of patient visits to sentinel physicians in the Pacific region were due to ILI.
Influenza Activity as Assessed by State and Territorial Epidemiologists**: Influenza activity was reported as widespread in Texas and regional in Arkansas, Colorado, Georgia, Kentucky, Maryland, and Tennessee. Thirty-five states reported sporadic influenza activity, 7 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.
*** 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 21, 2000
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