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

2011-2012 Influenza Season Week 8 ending February 25, 2012

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


During week 8 (February 19-25, 2012), influenza activity in the United States increased slightly, but remained relatively low.

  • U.S. Virologic Surveillance: Of the 3,947 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, 726 (18.4%) were positive for influenza.
  • Pneumonia and Influenza (P&I) Mortality Surveillance: The proportion of deaths attributed to P&I was below the epidemic threshold.
  • Influenza-associated Pediatric Mortality: One influenza-associated pediatric death was reported and was associated with an influenza virus for which the type was not determined.
  • Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 1.9%, which is below the national baseline of 2.4%. Regions 1, 5, and 7 reported ILI at or above region-specific baseline levels. Three states experienced high ILI activity; 2 states experienced moderate ILI activity; 6 states experienced low ILI activity; New York City and 39 states experienced minimal ILI activity, and the District of Columbia had insufficient data.
  • Geographic Spread of Influenza: Six states reported widespread geographic activity; 18 states reported regional influenza activity; 13 states reported local activity; the District of Columbia, Guam, Puerto Rico, and 12 states reported sporadic activity; the U.S. Virgin Islands reported no influenza activity, and one state did not report.

National and Regional Summary of Select Surveillance Components

HHS Surveillance Regions* Data for current week Data cumulative since October 2, 2011 (Week 40)
Out-patient ILI† % of respiratory specimens positive for flu‡ Number of jurisdictions reporting regional or widespread activity§ A (H3) 2009 H1N1 A(Subtyping not performed) B Pediatric Deaths
Nation Normal 18.4% 24 of 54 2,473 591 1,525 430 4
Region 1 Elevated 3.6% 1 of 6 44 10 3 22 0
Region 2 Normal 5.7% 1 of 4 40 14 37 24 0
Region 3 Normal 5.6% 1 of 6 89 25 30 20 0
Region 4 Normal 10.1% 3 of 8 175 54 427 149 1
Region 5 Elevated 43.1% 4 of 6 806 55 44 56 0
Region 6 Normal 11.7% 2 of 5 69 110 223 48 1
Region 7 Elevated 20.7% 4 of 4 338 22 142 13 0
Region 8 Normal 17.2% 5 of 6 384 48 529 21 0
Region 9 Normal 22.0% 2 of 5 390 225 81 41 2
Region 10 Normal 10.1% 1 of 4 138 28 9 36 0

*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 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 8
No. of specimens tested 3,947
No. of positive specimens (%) 726 (18.4%)
Positive specimens by type/subtype
  Influenza A 696 (95.9%)
             2009 H1N1 71 (10.2%) 
             Subtyping not performed 319 (45.8%) 
             (H3) 306 (44.0%) 
  Influenza B 30 (4.1%)

Nationally, a low but increasing number of influenza positive specimens have been reported this season, with influenza A (H3N2) viruses being most common. However, there are regional differences in activity levels and which viruses predominate. Over the past several weeks, the proportion of 2009 H1N1 viruses identified has increased nationally and in several regions, most notably in Regions 6, 8, and 9.

INFLUENZA Virus Isolated
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Antigenic Characterization:

CDC has antigenically characterized 572 influenza viruses [87 2009 H1N1, 407 influenza A (H3N2) viruses, and 78 influenza B viruses] collected by U.S. laboratories since October 1, 2011.

2009 H1N1 [87]

  • Eighty-five (97.7%) of the 87 viruses were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2011-2012 influenza vaccine for the Northern Hemisphere.
  • Two viruses (2.3%) tested showed reduced titers with antiserum produced against A/California/7/2009.

Influenza A (H3N2) [407]

  • Three hundred nineteen (78.4%) of the 407 viruses were characterized as A/Perth/16/2009-like, the influenza A (H3N2) component of the 2011-2012 influenza vaccine for the Northern Hemisphere.
  • Eighty-eight viruses (21.6%) tested showed reduced titers with antiserum produced against A/Perth/16/2009.

Influenza B (B/Victoria/02/87 and B/Yamagata/16/88 lineages) [78]:

  • Victoria Lineage [36]: Thirty-six (46.2%) of the 78 influenza B viruses tested belong to the B/Victoria lineage of viruses and were characterized as B/Brisbane/60/2008-like, the influenza B component of the 2011-2012 Northern Hemisphere influenza vaccine.
  • Yamagata Lineage [42]: Forty-two (53.8%) of the 78 influenza B viruses tested belong to the B/Yamagata lineage of viruses.

Only a small number of influenza B viruses from the United States have been available for testing so far this season. While less than 50% of these viruses are similar to the influenza B component in the 2011-2012 influenza vaccine, the majority of influenza B viruses circulating worldwide have been similar to the influenza vaccine strain.

Composition of the 2012-2013 Influenza Vaccine:

The World Health Organization (WHO) has recommended vaccine viruses for the 2012-2013 Northern Hemisphere trivalent influenza vaccine, and FDA’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) has made recommendations for the composition of the 2012-2013 U.S. influenza vaccine. Both agencies recommend that the vaccine contain A/California/7/2009-like (2009 H1N1), A/Victoria/361/2011-like (H3N2), and B/Wisconsin/1/2010-like (B/Yamagata lineage) viruses. This recommendation changes the influenza A (H3N2) and influenza B components from the 2011-2012 Northern Hemisphere vaccine formulation. This recommendation was based on surveillance data related to epidemiology and antigenic characteristics, serological responses to 2011-2012 trivalent seasonal vaccines, and the availability of candidate strains and reagents.

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 mutation in the neuraminidase of the virus known to confer oseltamivir resistance (H275Y). The data summarized below combine the results of both testing methods. These samples are routinely obtained for surveillance purposes rather than for diagnostic testing of patients suspected to be infected with antiviral resistant virus.

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). As a result of the sustained high levels of resistance, data from adamantane resistance testing are not presented in the table below.

Neuraminidase Inhibitor Resistance Testing Results on Samples Collected Since October 1, 2011

Oseltamivir Zanamivir
Virus Samples tested (n) Resistant Viruses, Number (%) Virus Samples tested (n) Resistant Viruses, Number (%)
Influenza A (H3N2) 416 0 (0.0) 416 0 (0.0)
Influenza B 76 0 (0.0) 76 0 (0.0)
2009 H1N1 129 1 (0.2) 104 0 (0.0)

The first oseltamivir resistant 2009 H1N1 virus detected in the U.S. during the 2011-2012 influenza season is being reported this week. Rare sporadic cases of oseltamivir resistant 2009 H1N1 and A (H3N2) viruses have been detected worldwide. Antiviral treatment with oseltamivir or zanamivir is recommended as early as possible for patients with confirmed or suspected influenza who have severe, complicated, or progressive illness; who require hospitalization; or who are at greater risk for influenza-related complications. Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available at (

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 8, 7.3% of all deaths reported through the 122-Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 7.9% for week 8.

Pneumonia And Influenza Mortality
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Influenza-Associated Pediatric Mortality:

One influenza-associated pediatric death was reported to CDC during week 8 and was associated with an influenza virus for which the type was not determined. The death reported during week 8 occurred during the week ending February 4, 2012 (week 5). This brings the total number of influenza-associated pediatric deaths reported during the 2011-2012 season to four.

Influenza-Associated Pediatric Mortality
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Influenza-Associated Hospitalizations:

The Influenza Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-associated hospitalizations in children younger than 18 years of age (since the 2003-2004 influenza season) and adults (since the 2005-2006 influenza season).

The FluSurv-NET covers more than 80 counties in the 10 Emerging Infections Program (EIP) states (CA, CO, CT, GA, MD, MN, NM, NY, OR, TN) and additional Influenza Hospitalization Surveillance Project (IHSP) states. The IHSP began during the 2009-2010 season to enhance surveillance during the 2009 H1N1 pandemic. IHSP sites included IA, ID, MI, OK and SD during the 2009-2010 season; ID, MI, OH, OK, RI, and UT during the 2010-2011 season; and MI, OH, RI, and UT during the 2011-2012 season. The rates provided are likely to be a vast underestimate of the actual number of influenza-associated hospitalizations. First, the FluSurv-NET is not nationally representative, and second, influenza-associated hospitalizations can be missed, either because testing is not performed, or because cases may be attributed to other causes of pneumonia or other common influenza-related complications.

Between October 1, 2011 and February 25, 2012, 437 laboratory-confirmed influenza-associated hospitalizations were reported at a rate of 1.6 per 100,000 population. Among cases, 376 (86.0%) were influenza A, 51 (11.7%) were influenza B, and 1 (0.2%) was an influenza A and B co-infection; 9 (2.1%) had no virus type information. Among those with influenza A subtype information, 145 were H3N2 and 38 were 2009 H1N1. The most commonly reported underlying medical conditions among adults were chronic lung diseases, metabolic disorders and obesity. The most commonly reported underlying medical conditions in children were chronic lung diseases, asthma and neurologic disorders. However, almost half of hospitalized children had no identified underlying medical conditions.

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Underlying medical conditions

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Outpatient Illness Surveillance:

Nationwide during week 8, 1.9% 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 2.4%. (ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)

national levels of ILI and ARI
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On a regional level, the percentage of outpatient visits for ILI ranged from 0.9% to 2.9% during week 8. Regions 5 and 7 reported a proportion of outpatient visits for ILI at or above 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 being below the average, to intense, which would correspond to ILI activity being much higher than 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 8, the following ILI activity levels were experienced:

  • Three states experienced high ILI activity (Alabama, Missouri, and Oklahoma)
  • Two states experienced moderate ILI activity (Illinois and Kansas)
  • Six states and New York City experienced low ILI activity (Colorado, Mississippi, Nevada, South Dakota, Texas, and Utah)
  • Thirty-nine states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Indiana, Iowa, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oregon, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming)
  • Data were insufficient to calculate an ILI activity level from the District of Columbia

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*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 here by CDC and independently by some 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 intensity of influenza activity.

During week 8, the following influenza activity was reported:

  • Widespread influenza activity was reported by 6 states (California, Colorado, Illinois, Nevada, Oklahoma, and Virginia)
  • Regional influenza activity was reported by 18 states (Alabama, Florida, Iowa, Kansas, Kentucky, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, New York, South Dakota, Texas, Utah, Washington, Wisconsin, and Wyoming)
  • Local influenza activity was reported by 13 states (Arizona, Arkansas, Connecticut, Georgia, Idaho, Louisiana, Mississippi, New Hampshire, New Mexico, North Dakota, Ohio, Pennsylvania, and South Carolina)
  • Sporadic influenza activity was reported by the District of Columbia, Guam, Puerto Rico, and 12 states (Alaska, Delaware, Hawaii, Indiana, Maine, Maryland, North Carolina, Oregon, Rhode Island, Tennessee, Vermont, and West Virginia)
  • No influenza activity was reported by the U.S. Virgin Islands
  • One state (New Jersey) did not report

U. S. Map for Weekly Influenza Activity

Flu Activity data in XML Format | View Full Screen

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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.









District of Columbia





















New Hampshire

New Jersey

New Mexico

New York

North Carolina

North Dakota





Rhode Island

South Carolina

South Dakota







West Virginia



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

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 United States. For more information and activity estimates from the U.S. and worldwide, see

Europe: for the most recent influenza surveillance information from Europe, please see WHO/Europe at and visit the European Centre for Disease Prevention and Control at

Public Health Agency of Canada: The most up-to-date influenza information from Canada is available at

World Health Organization FluNet: Additional influenza surveillance information from participating WHO member nations is available at FluNet and the Global Epidemiology Reports


A description of surveillance methods is available at:

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