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Weekly Report: Influenza Summary Update

2007-2008 Influenza Season Week 42, ending October 20, 2007

(All data are preliminary and may change as more reports are received.)

Synopsis

During week 42 (October 14-20, 2007), a low level of influenza activity was reported in the United States.
  • Twenty-nine (2.2%) 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 deaths attributed to pneumonia and influenza was slightly above the epidemic threshold.
  • The proportion of outpatient visits for influenza-like illness (ILI) and acute respiratory illness (ARI) was below national and region-specific baseline levels.
  • Thirteen states, the District of Columbia, and Puerto Rico reported sporadic influenza activity; and 37 states reported no influenza activity.

National and Regional Summary of Select Surveillance Components

Region Data for current week Data cumulative for the season
Sentinel Provider ILI* DoD and VA ARI* % pos. for flu† # jurisdictions reporting regional or widespread activity‡ A (H1) A (H3) A Unsub-typed B Pediatric Deaths
Nation Normal Normal 2.2% 0 of 51 10 1 64 4 0
New England Normal Normal 0.7% 0 of 6 2 0 0 0 0
Mid-Atlantic Normal Normal 0% 0 of 3 0 0 0 0 0
East North Central Normal Normal 0% 0 of 5 0 0 0 0 0
West North Central Normal Normal 0.8% 0 of 7 0 0 4 0 0
South Atlantic Normal Normal 4.0% 0 of 9 0 1 30 1 0
East South Central Normal Normal 0% 0 of 4 0 0 0 0 0
West South Central Normal Normal 1.5% 0 of 4 0 0 15 0 0
Mountain Normal Normal 1.9% 0 of 8 5 0 1 0 0
Pacific Normal Normal 3.2% 0 of 5 3 0 14 3 0

* Elevated means the % of visits for ILI or ARI is at or above the national or region-specific baseline
† National data is for current week; regional data is for the most recent 3 weeks.
‡ Includes all 50 states and the District of Columbia

Laboratory Surveillance

During week 42, WHO and NREVSS laboratories reported 1,349 specimens tested for influenza viruses, 29 (2.2%) of which were positive, including two influenza A (H1) viruses (New England region) and 27 influenza A viruses that were not subtyped (Mountain, Pacific, South Atlantic, and West North Central, West South Central regions).

INFLUENZA Virus Isolated
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Pneumonia and Influenza (P&I) Mortality Surveillance

During week 42, 6.1% of all deaths reported through the 122-Cities Mortality Reporting System were reported as due to P&I. This percentage is above the epidemic threshold of 5.9% for week 42. This is the seventh consecutive week that the percentage of deaths due to P&I has been above the epidemic threshold. No other component of the national surveillance system showed evidence of increased influenza activity or virus circulation. Both national and regional percentages of death due to P&I during the last seven weeks are similar to the percentages reported during this time period last year. The baseline percentage of P&I deaths is projected for the current season based on P&I data from the previous five years. The five-year period used to project the current season’s baseline included three mild seasons, therefore, the elevation relative to the baseline may be due to in part to the lowering of the baseline values. However, potential explanations for the increase in P&I mortality above threshold continue to be investigated.

Pneumonia And Influenza Mortality
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Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported during week 42.

Influenza-Associated Pediatric Mortality
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Influenza-Associated Pediatric Hospitalizations

Laboratory-confirmed influenza-associated pediatric hospitalizations are monitored in two population-based surveillance networks: the Emerging Infections Program (EIP) and the New Vaccine Surveillance Network (NVSN). EIP estimated rates of hospitalization for influenza will be reported every two weeks beginning October 26, 2007. NVSN estimated rates of hospitalization for influenza will be reported every two weeks, beginning November 30, 2007.

Outpatient Illness Surveillance

Nationwide during week 42, 1.3% of patient visits reported through the U.S. Influenza Sentinel Provider Surveillance Network were due to influenza-like illness (ILI) and 1.8% of patient visits to Department of Veteran’s Affairs (VA) and Department of Defense (DoD) outpatient treatment facilities were for acute respiratory illness (ARI). These percentages are less than the national baseline of 2.2% and 3.2%, respectively. On a regional level, the percentage of visits for ILI ranged from 0.5% to 3.4% and the percentage of visits for ARI ranged from 0.8% to 2.2%. All nine regions reported percentages of visits for ILI and ARI below their respective region-specific baselines. All five age groups reported percentages of visits for ARI below their respective age-specific baselines.

national levels of ILI and ARI
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Bar Chart for Influenza-like Illness
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Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists

Influenza activity was reported as sporadic in 13 states (Alaska, California, Colorado, Connecticut, Florida, Hawaii, Indiana, Kentucky, Massachusetts, Nevada, New York, North Carolina, and Utah), the District of Columbia, and Puerto Rico. Thirty-seven states reported no influenza activity.

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A description of surveillance methods is available at: http://www.cdc.gov/flu/weekly/fluactivity.htm

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