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Influenza (Flu) - Protect Yourself and Your Loved Ones
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Weekly Report: Influenza Summary Update
Week ending January 20, 2001-Week 03

The following information may be quoted:

Synopsis:

During week 3 (January 14-20, 2001)*, 22 % of the specimens tested by WHO and NREVSS laboratories were positive for influenza. 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 6 of 9 surveillance regions. The proportion of deaths attributed to pneumonia and influenza was 7,9 %. This percentage is below the epidemic threshold for this time of year. Twelve state and territorial health departments reported widespread influenza activity**, 18 reported regional influenza activity, and 19 reported sporadic activity.

U.S. World Health Organization (WHO) and National Respiratory And Enteric Virus Surveillance System(NREVSS)Collaborating Laboratory Reports *:

During week 3, WHO and NREVSS laboratories reported 1 772 specimens tested for influenza viruses, of which 398 (22 %) were positive. Sixty-four (16 %) were influenza A (H1N1) viruses, 239 (60 %) were unsubtyped influenza A viruses, and 95 (24 %) were influenza B viruses. Between 22 % and 30 % of specimens tested for influenza over the past 3 weeks (weeks 1-3) in the South Atlantic, East North Central, West South Central, and New England regions*** were positive. In 4 regions (Pacific, Mountain, East South Central, and West North Central), the percentage of specimens testing positive for influenza in the past 3 weeks ranged from 11 % to 19 %. The percentage of specimens testing positive for influenza in the Mid-Atlantic region was 7 %.

Since October 1, WHO and NREVSS laboratories have tested a total of 30 034 specimens for influenza viruses, and 2 239 (7 %) were positive. Of the 2 239 isolates identified, 1 640 (73 %) were influenza type A and 599 (27 %) were influenza type B. Six hundred and twenty-six (38 %) of the 1 640 influenza A viruses identified have been subtyped; 605 (97 %) were A (H1N1) and 21 (3 %) were A (H3N2). Influenza A viruses have predominated (range 65 % to 88 %) in 6 regions (East North Central, Mountain, New England, South Atlantic, West North Central, and West South Central), and influenza B viruses have predominated (range 57 % to 62 %) in the Mid-Atlantic region and Pacific regions. The East South Central region has reported approximately equal numbers of influenza A and influenza B isolates.

 Influenza Virus Isolated

Antigenic Characterization of Viral Isolates:

CDC has antigenically characterized 153 influenza viruses received from U.S. laboratories since October 1. Of the 122 influenza A (H1N1) isolates that have been characterized, 114 (93 %) were similar to A/New Caledonia/20/99, the H1N1 component of the 2000-01 influenza vaccine, and 8 (7 %) were similar to A/Bayern/07/95. Although A/Bayern-like viruses are antigenically distinct from the A/New Caledonia-like viruses, the A/New Caledonia/20/99 vaccine strain produces high titers of antibody that cross-react with A/Bayern/07/95-like viruses. Of the 10 influenza A (H3N2) viruses and the 21 influenza B viruses that have been characterized, all were antigenically similar to vaccine strains A/Panama/2007/99 (H3N2) and B/Beijing/184/93, respectively.

Pneumonia and Influenza (P&I) Mortality:

During week 3, the percentage of all deaths due to P&I as reported by the vital statistics offices of 122 U.S. cities was 7,9 %. This percentage is below the epidemic threshold of 8,6 % for week 3.

Pneumonia And Influenza Mortality

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Influenza Morbidity Reports from U.S. Sentinel Physicians*:

During week 3, 3 % of patient visits to U.S. sentinel physicians were due to influenza-like illness (ILI). The percentage of patient visits for ILI was above baseline levels of 0 % to 3 % in 3 of 9 surveillance regions (Mountain [4 %], Pacific [6 %], and West South Central [7 %]).

Bar Chart for Influenza-like Illness

Influenza Activity as Assessed by State and Territorial Epidemiologists**:

Influenza activity was reported as widespread in 12 states (Arizona, Colorado, Connecticut, Maryland, Minnesota, Mississippi, North Carolina, Oregon, Rhode Island, Tennessee, Utah, and Virginia) and regional in 18 states (Alabama, California, Idaho, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, Missouri, Nebraska, Nevada, New Hampshire, New York, Pennsylvania, Texas, Washington, and Wyoming). Nineteen states reported sporadic influenza activity and 1 state did not report.

Usmap for Weekly Influenza Activity


* 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: January 25, 2001

 

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