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FluView: A Weekly Influenza Surveillance Report Prepared by the Influenza Division

2010-2011 Influenza Season Week 14 ending April 9, 2011


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

Synopsis:

During week 14 (April 3-9, 2011), influenza activity in the United States continued to decrease.

  • Of the 4,234 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division, 387 (9.1%) were positive for influenza.
  • The proportion of deaths attributed to pneumonia and influenza (P&I) has been at or above the epidemic threshold for 11 consecutive weeks.
  • One influenza-associated pediatric death was reported, bringing the season total to 91. This death was associated with an influenza B virus.
  • The proportion of outpatient visits for influenza-like illness (ILI) was 1.4%, which is below the national baseline of 2.5%. All 10 regions reported ILI below region-specific baseline levels. Two states experienced low ILI activity; 48 states and New York City experienced minimal ILI activity, and the District of Columbia had insufficient data to calculate an ILI activity levell.
  • The geographic spread of influenza in two states was reported as widespread; nine states reported regional influenza activity; the District of Columbia and 23 states reported local influenza activity; Guam and 16 states reported sporadic influenza activity; the U.S. Virgin Islands reported no influenza activity, and Puerto Rico did not report.

National and Regional Summary of Select Surveillance Components

HHS Surveillance Regions* Data for current week Data cumulative since October 3, 2010 (Week 40)
Out-patient ILI† % positive for flu‡ Number of jurisdictions reporting regional or widespread activity§ A (H3) 2009 A (H1N1) A(Subtyping not performed) B Pediatric Deaths
Nation Normal 9.1% 11 of 54 16,357 10,715 11,123 13,226 91
Region 1 Normal 23.1% 3 of 6 1,668 880 91 416 3
Region 2 Normal 17.2% 2 of 4 728 355 1,099 415 9
Region 3 Normal 16.5% 2 of 6 2,937 2,572 847 951 10
Region 4 Normal 5.9% 0 of 8 1,448 1,426 3,120 3,932 16
Region 5 Normal 32.2% 1 of 6 1,955 1,519 386 1,172 16
Region 6 Normal 6.9% 0 of 5 2,186 558 2,291 2,559 16
Region 7 Normal 10.1% 0 of 4 705 537 283 670 1
Region 8 Normal 11.5% 1 of 6 1,694 666 2,093 1,821 7
Region 9 Normal 8.0% 1 of 5 1,948 1,407 733 1,163 11
Region 10 Normal 19.2% 1 of 4 1,088 795 180 127 2

*HHS regions (Region 1 CT, ME, MA, NH, RI, VT; Region 2: NJ, NY, Puerto Rico, US Virgin Islands; Region 3: DE, DC, MD, PA, VA, WV; Region 4: AL, FL, GA, KY, MS, NC, SC, TN; Region 5: IL, IN, MI, MN, OH, WI; Region 6: AR, LA, NM, OK, TX; Region 7: IA, KS, MO, NE; Region 8: CO, MT, ND, SD, UT, WY; Region 9: AZ, CA, Guam, HI, NV; and Region 10: AK, ID, OR, WA).
† Elevated means the % of visits for ILI is at or above the national or region-specific baseline
‡ National data are for current week; regional data are for the most recent three weeks
§ Includes all 50 states, the District of Columbia, Guam, Puerto Rico, and U.S. Virgin Islands

U.S. Virologic Surveillance:

WHO and NREVSS collaborating laboratories located in all 50 states and Washington D.C. report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza type and subtype. The results of tests performed during the current week are summarized in the table below.

Week 14
No. of specimens tested 4,234
No. of positive specimens (%) 387 (9.1%)
Positive specimens by type/subtype
  Influenza A 242 (62.5%)
             A (2009 H1N1) 68 (28.1%) 
             A (subtyping not performed) 74 (30.6%) 
             A (H3) 100 (41.3%) 
  Influenza B 145 (37.5%)

All influenza types and subtypes have been identified at high levels this season and continue to circulate . The predominant virus has varied by week, region, and even between states within the same region. In recent weeks the proportion of influenza B viruses identified nationally and in some regions has been increasing and in week 14 two of the 10 regions (Regions 1 and 2) reported more influenza B viruses than influenza A viruses.


INFLUENZA Virus Isolated
View WHO-NREVSS Regional Bar Charts | View Chart Data | View Full Screen | View PowerPoint Presentation


Aggregate Hospitalization and Death Reporting Activity (AHDRA):

This system tracks weekly counts of laboratory-confirmed influenza-associated hospitalizations and deaths and was implemented on August 30, 2009, during the 2009 pandemic, and ended on April 4, 2010. AHDRA surveillance during the 2010-11 season is being continued on a voluntary basis, and 16 jurisdictions reported during week 14. From October 3, 2010 – April 9, 2011, 15,630 laboratory-confirmed influenza associated hospitalizations and 298 laboratory-confirmed influenza associated deaths were reported to CDC.


Aggregate Hospital and Death Reporting
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| View Chart Data | View PowerPoint Presentation


Antigenic Characterization:

CDC has antigenically characterized 1,810 influenza viruses [424 2009 influenza A (H1N1) viruses, 841 influenza A (H3N2) viruses, and 545 influenza B viruses] collected by U.S. laboratories since October 1, 2010.

    2009 Influenza A (H1N1) [424]

  • Four hundred twenty-three (99.8%) of the 424 tested were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2010-11 influenza vaccine for the Northern Hemisphere. One virus (0.2%) of the 424 tested showed reduced titers with antiserum produced against A/California/7/2009.

    Influenza A (H3N2) [841]

  • Eight hundred twelve (96.6%) of the 841 tested were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2010-11 influenza vaccine for the Northern Hemisphere. Twenty-nine viruses (3.4%) of the 841 tested showed reduced titers with antiserum produced against A/Perth/16/2009.

    Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) [545]
    Victoria Lineage [516]

  • Five hundred sixteen (94.7%) of the 545 influenza B viruses tested belong to the B/Victoria lineage of viruses.
    • Five hundred fifteen (99.8%) of these 516 viruses were characterized as B/Brisbane/60/2008-like, the recommended influenza B component for the 2010-11 Northern Hemisphere influenza vaccine.
    • One (0.2%) of these 516 viruses showed somewhat reduced titers with antisera produced against B/Brisbane/60/2008.

    Yamagata Lineage [29]

  • Twenty-nine (5.3%) of the 545 viruses were identified as belonging to the B/Yamagata lineage of viruses.

Antiviral Resistance:

Testing of 2009 influenza A (H1N1), influenza A (H3N2), and influenza B virus isolates for resistance to neuraminidase inhibitors (oseltamivir and zanamivir) is performed at CDC using a functional assay. Additional 2009 influenza A (H1N1) clinical samples are tested for a single known mutation in the neuraminidase protein of the virus that confers oseltamivir resistance (H275Y). The data summarized below combine the results of both test methods and includes samples that were tested as part of routine surveillance purposes; it does not include diagnostic testing specifically done because of clinical suspicion of antiviral resistance.

High levels of resistance to the adamantanes (amantadine and rimantadine) persist among 2009 influenza A (H1N1) and A (H3N2) viruses (the adamantanes are not effective against influenza B viruses) circulating globally. As a result of the sustained high levels of resistance, data from adamantane resistance testing are not presented weekly in the table below.

Neuraminidase Inhibitor Resistance Testing Results on Samples Collected Since October 1, 2010

Virus
Samples
tested (n)
Resistant
Viruses,
  Number (%)  
Oseltamivir
Virus
Samples
tested (n)
Resistant
Viruses,
  Number (%)  
Zanamivir
Seasonal Influenza A (H1N1) 0 0 (0.0) 0 0 (0.0)
Influenza A (H3N2) 627 2 (0.3) 627 0 (0.0)
Influenza B 518 0 (0.0) 518 0 (0.0)
2009 Influenza A (H1N1) 2,561* 18 (0.7) 396 0 (0.0)

*Includes specimens collected and tested through national surveillance and additional specimens tested at public health laboratories in six states (CA, ME, MD, MN, TX, and WA) who share testing results with CDC.

To prevent the spread of antiviral resistant virus strains, CDC reminds clinicians and the public of the need to continue hand and cough hygiene measures for the duration of any symptoms of influenza, even while taking antiviral medications. Additional information on antiviral recommendations for treatment and chemoprophylaxis of influenza virus infection is available at http://www.cdc.gov/flu/antivirals/index.htm.

Pneumonia and Influenza (P&I) Mortality Surveillance

During week 14, 8.0% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was above the epidemic threshold of 7.8% for week 14 and is the eleventh consecutive week in which P&I has been at or above the epidemic threshold.

Pneumonia And Influenza Mortality
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Influenza-Associated Pediatric Mortality

One influenza-associated pediatric death was reported to CDC during week 14. This death was associated with an influenza B virus. One pediatric death reported during week 12 was reclassified by the reporting jurisdiction as not due to influenza. The total number of influenza associated pediatric deaths occurring during the current season remains 91.

Ninety-one deaths from 33 states, Chicago, and New York City have been reported during this influenza season. Thirty-four of the 91 deaths reported were associated with influenza B viruses; 23 were associated with 2009 influenza A (H1N1) viruses; 17 deaths reported were associated with influenza A (H3N2) viruses, and 17 were associated with an influenza A virus for which the subtype was not determined.


Influenza-Associated Pediatric Mortality
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Influenza-Associated Hospitalizations

FluSurv-NET conducts population-based surveillance for laboratory-confirmed influenza-associated hospitalizations in children (persons younger than 18 years) and adults. The current network covers over 80 counties in the 10 Emerging Infections Program (EIP) states (CA, CO, CT, GA, MD, MN, NM, NY, OR, and TN) and six additional states (ID, MI, OH, OK, RI, and UT).

The current season’s rates include cases from October 1, 2010 to April 9, 2011.

Influenza-Associated Pediatric Mortality
Influenza-Associated Pediatric Mortality
Click here to view rates for 2010-2011 season | View PowerPoint Presentation

Click here to view rates for 2009-2010 season
Click here to view rates for 2008-2009 season
Click here to view rates for 2007-2008 season


Please note the following: (i) The scale of the vertical axis on the Cumulative Hospitalization Rate figures will be adjusted during the season to make the graphs easier to read; (ii) FluSurv-NET was created during the 2009-2010 season when surveillance in six states was added to ongoing surveillance for influenza-associated hospitalizations in10 EIP states. During the 2009-2010 season, FluSurv-NET included sites in the 10 EIP sites and sites in IA, ID, MI, ND, OK, and SD; (iii) the 2008-2009 EIP season ended April 14, 2009, due to the onset of the 2009 H1N1 pandemic.





Influenza-Associated Pediatric Mortality
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1Asthma may include a diagnosis of asthma and reactive airway disease; Cardiovascular diseases may include conditions such as coronary heart disease, cardiac valve disorders, congestive heart failure, pulmonary hypertension, and aortic stenosis; Chronic lung diseases may include conditions such as bronchiolitis obliterans, chronic aspiration pneumonia, and interstitial lung disease; Immune suppression may include conditions such as immunoglobulin deficiency, leukemia, lymphoma, HIV/AIDS, and individuals taking immunosuppressive medications; Metabolic disorders may include conditions such as diabetes mellitus, thyroid dysfunction, adrenal insufficiency, and liver disease; Neurologic diseases may include conditions such as seizure disorders, neuromuscular disorders, and cognitive dysfunction; Obesity was defined as a body mass index (BMI) greater than 30 kg/m2 in patients 20 years of age or older, or equal to or greater than the 95th percentile of a patient’s age and sex category in patients under 20 years of age; Renal diseases may include conditions such as acute or chronic renal failure, nephrotic syndrome, glomerulonephritis, and impaired creatinine clearance.
22Data as of April 12, 2011. Includes 3,348 (of a total 5,705 reported) cases for which data collection has been completed through the medical chart review stage.

Demographic and clinical characteristics of laboratory-confirmed, influenza-associated hospitalizations identified in EIP1 and FluSurv-NET2 sites, 2006-2011

 

2010-2011
FluSurv-NET3
N (%)
2009-2010
FluSurv-NET
N (%)
2008-2009
EIP
N (%)
2007-2008
EIP
N (%)
2006-2007
EIP
N (%)
Total Cases 5,705 7,517 1,698 3,930 1,279
Age in Years      
0-4  872 (15.3)  1,326 (17.6)  549 (32.3)  639 (16.3)  393 (30.7)
5-17  409 (7.2)  1,204 (16.0)  244 (14.4)  221 (5.6)  130 (10.2)
18-49  1,412 (24.8)  2,779 (37.0)  374 (22.0)  736 (18.7)  246 (19.2)
50-64  1,102 (19.3)  1,458 (19.4)  201 (11.8)  585 (14.9)  155 (12.1)
65+  1,908 (33.4)  750 (10.0)  330 (19.4)  1,749 (44.5)  355 (27.8)
Sex      
Male  2,654 (46.5)  3,517 (46.8)  832 (49.0)  1,825 (46.4)  631 (49.3)
Female  3,047 (53.4)  4,000 (53.2)  866 (51.0)  2,104 (53.5)  648 (50.7)
Flu Type and Subtype      
Influenza A  4,678 (82.0)  7,355 (97.8)  1,236 (72.8)  2,562 (65.2)  1,082 (84.6)
    Specimens subtyped4  1,457  5,325  --            --            --          
        A (H1)  0 (0.0)  0 (0.0)  --            --            --          
        A (H3)  983 (67.5)  3 (0.1)  --            --            --          
        A (2009 H1N1)  474 (32.5)  5,322 (99.9)  --            --            --          
Influenza B  897 (15.7)  52 (0.7)  382 (22.5)  1,199 (30.5)  149 (11.6)
Intensive Care Unit  553 (16.5)  1,560 (20.8)  298 (17.6)  495 (12.6)  198 (15.5)
Mechanical Ventilation  249 (7.4)  758 (10.1)  157 (9.2)  252 (6.4)  111 (8.7)
Diagnosis of Pneumonia  929 (27.7)  2,804 (37.3)  407 (24.0)  1,220 (31.0)  404 (31.6)
Died  80 (2.4)  222 (3.0)  49 (2.9)  104 (2.6)  24 (1.9)

Columns may not sum to 100% due to missing or unknown values.
1Surveillance in EIP states (CA, CO, CT, GA, MD, MN, NM, NY, OR, TN) was conducted from 2006-2011.
2FluSurv-Net includes surveillance at EIP sites and at sites in additional states (IA, ID, MI, ND, OK, SD in 2009-2010; ID, MI, OH, OK, RI, UT in 2010-2011).
33Data as of April 12, 2011. Results describing influenza A subtype, intensive care unit admission, mechanical ventilation, diagnosis of pneumonia, and death are from 3,348 (of a total 5,705 reported) cases for which data collection has been completed through the medical chart review stage.
4Influenza A subtype results are available beginning with the 2007-2008 season. Percentages for influenza A subtypes are calculated using the number of influenza A specimens that were subtyped as a denominator.


Outpatient Illness Surveillance:

Nationwide during week 14, 1.4% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI). This percentage is below the national baseline of 2.5%.

national levels of ILI and ARI
View ILINet Regional Charts | View Chart Data | View Full Screen | View PowerPoint Presentation

On a regional level, the percentage of outpatient visits for ILI ranged from 0.8% to 1.9% during week 14. All 10 regions reported ILI below region-specific baseline levels.

ILINet State Activity Indicator Map:

Data collected in ILINet are used to produce a measure of ILI activity* by state. Activity levels are based on the percent of outpatient visits in a state due to ILI and are compared to the average percent of ILI visits that occur during spring and fall weeks with little or no influenza virus circulation. Activity levels range from minimal, which would correspond to ILI activity from outpatient clinics being below the average, to high, which would correspond to ILI activity from outpatient clinics being much higher than the average. Because the clinical definition of ILI is very general, not all ILI is caused by influenza; however, when combined with laboratory data, the information on ILI activity provides a clear picture of influenza activity in the United States.

During week 14, the following ILI activity levels were experienced:

  • Low ILI activity was experienced by two states (Alaska and Idaho).
  • Minimal ILI activity was experienced by New York City and 48 states (Alabama, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).
  • The District of Columbia had insufficient data to calculate an activity level.

Click on map to launch interactive tool

Click on map to launch interactive tool

*This map uses the proportion of outpatient visits to health care providers for influenza-like illness to measure the ILI activity level within a state. It does not, however, measure the extent of geographic spread of flu within a state. Therefore, outbreaks occurring in a single city could cause the state to display high activity levels.
Data collected in ILINet may disproportionately represent certain populations within a state, and therefore, may not accurately depict the full picture of influenza activity for the whole state.
Data displayed in this map are based on data collected in ILINet, whereas the State and Territorial flu activity map are based on reports from state and territorial epidemiologists. The data presented in this map is preliminary and may change as more data is received.
Differences in the data presented by CDC and state health departments likely represent differing levels of data completeness with data presented by the state likely being the more complete.

Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists:

The influenza activity reported by state and territorial epidemiologists indicates geographic spread of influenza viruses, but does not measure the severity of influenza activity.

During week 14, the following influenza activity was reported:

  • Widespread influenza activity was reported by two states (Maine and New York).
  • Regional influenza activity was reported by nine states (Alaska, Connecticut, Hawaii, Maryland, Minnesota, Montana, New Hampshire, New Jersey, and Virginia).
  • Local influenza activity was reported by the District of Columbia and 23 states (Alabama, Arizona, California, Georgia, Idaho, Iowa, Louisiana, Massachusetts, Michigan, Missouri, Nebraska, Nevada, New Mexico, North Dakota, Ohio, Oklahoma, Pennsylvania, South Carolina, South Dakota, Utah, Vermont, Washington, and Wisconsin).
  • Sporadic influenza activity was reported by Guam and 16 states (Arkansas, Colorado, Delaware, Florida, Illinois, Indiana, Kansas, Kentucky, Mississippi, North Carolina, Oregon, Rhode Island, Tennessee, Texas, West Virginia, and Wyoming).
  • The U.S. Virgin Islands reported no influenza activity.
  • Puerto Rico did not report.

U. S. Map for Weekly Influenza Activity

View Full Screen



Additional National and International Influenza Surveillance Information

U.S. State and local influenza surveillance: Click on a jurisdiction below to access the latest local influenza information.

Alabama

Alaska

Arizona

Arkansas

California

Colorado

Connecticut

Delaware

District of Columbia

Florida

Georgia

Hawaii

Idaho

Illinois

Indiana

Iowa

Kansas

Kentucky

Louisiana

Maine

Maryland

Massachusetts

Michigan

Minnesota

Mississippi

Missouri

Montana

Nebraska

Nevada

New Hampshire

New Jersey

New Mexico

New York

North Carolina

North Dakota

Ohio

Oklahoma

Oregon

Pennsylvania

Rhode Island

South Carolina

South Dakota

Tennessee

Texas

Utah

Vermont

Virginia

Washington

West Virginia

Wisconsin

Wyoming

New York City

Virgin Islands

Distribute Project: Additional information on the Distribute syndromic surveillance project, developed and piloted by the International Society for Disease Surveillance (ISDS) now working in collaboration with CDC, to enhance and support Emergency Department (ED) surveillance, is available at http://isdsdistribute.org/

Google Flu Trends: Google Flu Trends uses aggregated Google search data in a model created in collaboration with CDC to estimate influenza activity in the U.S. For more information and activity estimates from the U.S. and worldwide, see http://www.google.org/flutrends/

Europe: for the most recent influenza surveillance information from Europe, please see WHO/Europe at http://www.euroflu.org/index.php and visit the European Centre for Disease Prevention and Control at http://ecdc.europa.eu/en/publications/surveillance_reports/influenza/Pages/weekly_influenza_surveillance_overview.aspx

Public Health Agency of Canada: The most up to date influenza information from Canada is available at http://www.phac-aspc.gc.ca/fluwatch/

World Health Organization FluNet: Additional influenza surveillance information from participating WHO member nations is available at http://gamapserver.who.int/GlobalAtlas/home.asp

--------------------------------------------------------------------------------

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

 
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