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

2013-2014 Influenza Season Week 2 ending January 11, 2014

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


During week 2 (January 5-11, 2014), influenza activity remained high in the United States.

  • Viral Surveillance: Of 10,841 specimens tested and reported during week 2 by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, 2,721 (25.1%) were positive for influenza.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was above the epidemic threshold.
  • Influenza-Associated Pediatric Deaths: Ten influenza-associated pediatric deaths were reported.
  • Influenza-associated Hospitalizations: A cumulative rate for the season of 13.8 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported.
  • Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 3.6%, above the national baseline of 2.0%. All 10 regions reported ILI above region-specific baseline levels. Fourteen states experienced high ILI activity; 12 states experienced moderate ILI activity; eight states and New York City experienced low ILI activity; 16 states experienced minimal ILI activity, and the District of Columbia had insufficient data.
  • Geographic Spread of Influenza: The geographic spread of influenza in 40 states was reported as widespread; nine states and Guam reported regional influenza activity; the District of Columbia and Puerto Rico reported local influenza activity; one state reported sporadic influenza activity, and the U.S. Virgin Islands did not report.

A description of surveillance methods is available at:

National and Regional Summary of Select Surveillance Components

HHS Surveillance Regions* Data for current week Data cumulative since September 29, 2013 (Week 40)
Out-patient ILI† % positive for flu‡ Number of jurisdictions reporting regional or widespread activity§ 2009 H1N1 A (H3) A(Subtyping not performed) B Pediatric Deaths
Nation Elevated 25.1% 50 of 54 12,708 469 8,576 716 20
Region 1 Elevated 31.4% 6 of 6 461 35 75 15 1
Region 2 Elevated 19.4% 2 of 4 647 30 318 34 0
Region 3 Elevated 28.3% 5 of 6 1,424 43 62 18 1
Region 4 Elevated 21.5% 8 of 8 1,146 9 3,438 435 7
Region 5 Elevated 41.9% 6 of 6 1,372 46 335 15 1
Region 6 Elevated 28.3% 5 of 5 1,921 82 3,109 116 9
Region 7 Elevated 27.1% 4 of 4 744 17 37 11 0
Region 8 Elevated 33.6% 6 of 6 2,894 44 753 29 0
Region 9 Elevated 26.5% 4 of 5 892 104 364 30 0
Region 10 Elevated 35.8% 4 of 4 1,207 59 85 13 1

*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, Puerto Rico, and Washington D.C. report to CDC the number of respiratory specimens tested for influenza and the number positive by influenza virus type and influenza A virus subtype. The results of tests performed during the current week are summarized in the table below.

Region specific data can be found at

Week 2
No. of specimens tested 10,841
No. of positive specimens (%) 2,721 (25.1%)
Positive specimens by type/subtype
  Influenza A 2,662 (97.8%)
             2009 H1N1 1,730 (65.0%) 
              H3 55 (2.1%) 
            Subtyping not performed 877 (32.9%) 
  Influenza B 59 (2.2%)

INFLUENZA Virus Isolated
View National and Regional Level Graphs and Data | View Chart Data | View Full Screen | View PowerPoint Presentation

Antigenic Characterization*

CDC has antigenically characterized 736 influenza viruses [648 2009 H1N1 viruses, 72 influenza A (H3N2) viruses, and 16 influenza B viruses] collected by U.S. laboratories since October 1, 2013 by hemagglutination inhibition (HI).

2009 H1N1 [648]:

  • 647 (99.8%) of 648 2009 H1N1 viruses tested were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2013-2014 Northern Hemisphere influenza vaccine. One (0.2%) virus showed reduced titers with antiserum produced against A/California/7/2009.

Influenza A (H3N2) [72]:

  • All 72 influenza A (H3N2) viruses tested have been characterized as A/Texas/50/2012-like, the influenza A (H3N2) component of the 2013-2014 Northern Hemisphere influenza vaccine.

Influenza B [16]: Nine (56%) of the 16 influenza B viruses tested belong to B/Yamagata/16/88-lineage and the remaining seven (44%) influenza B viruses tested belong to B/Victoria/02/87 lineage.

  • Yamagata Lineage [9]: Nine influenza B/Yamagata-lineage viruses were characterized as B/ Massachusetts/2/2012-like, which is included as an influenza B component of the 2013-2014 Northern Hemisphere trivalent and quadrivalent influenza vaccines.
  • Victoria Lineage [7]: Seven influenza B/Victoria-lineage viruses were characterized as B/Brisbane/60/2008-like, which is included as an influenza B component of the 2013-2014 Northern Hemisphere quadrivalent influenza vaccine.

*For more information see the section on antigenic characterization in the MMWR “Update: Influenza Activity — United States and Worldwide, May 19–September 28, 2013”.

Antiviral Resistance

Testing of 2009 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 H1N1 and influenza A (H3N2) clinical samples are tested for mutations of the virus known to confer oseltamivir resistance. 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, data from adamantane resistance testing are not presented below.

Neuraminidase Inhibitor Resistance Testing Results on Samples Collected Since October 1, 2013

Oseltamivir Zanamivir
Virus Samples tested (n) Resistant Viruses, Number (%) Virus Samples tested (n) Resistant Viruses, Number (%)
Influenza A (H3N2) 85 0 (0.0) 85 0 (0.0)
Influenza B 20 0 (0.0) 20 0 (0.0)
2009 H1N1 1,553* 13 (0.8) 709 0 (0.0)

*Includes specimens tested in national surveillance and additional specimens tested at public health laboratories in 16 states (AZ, CO, DE, FL, GA, HI, MA, ME, MD, MI, NY, PA, TX, UT, WA, and WI) who share testing results with CDC.

The majority of currently circulating influenza viruses are susceptible to the neuraminidase inhibitor antiviral medications, oseltamivir and zanamivir; however, 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 serious 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 2, 7.5% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was above the epidemic threshold of 7.2% for week 2.

Pneumonia And Influenza Mortality
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Influenza-Associated Pediatric Mortality

Ten influenza-associated pediatric deaths were reported to CDC during week 2. Seven deaths were associated with a 2009 H1N1 virus and occurred during weeks 52, 1, and 2 (weeks ending December 28, 2013, January 4, and January 11, 2014). Two deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 51 and 2 (weeks ending December 21, 2013 and January 11, 2014) and one death was associated with an influenza virus for which the type was not determined and occurred during week 52 (week ending December 28, 2013).

A total of 20 influenza-associated pediatric deaths have been reported during the 2013-2014 season from 13 states (AR [2], FL [1], GA [1], KY [1], LA [1], MA [1], MI [1], MS [1], OK [1], OR [1], TN [3], TX [5], and WV [1]).

Additional data can be found at

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Influenza-Associated Hospitalizations

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related 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 70 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; MI, OH, RI, and UT during the 2011-2012 season; IA, MI, OH, RI, and UT during the 2012-2013 season; and MI, OH, and UT during the 2013-2014 season.

Data gathered are used to estimate age-specific hospitalization rates on a weekly basis, and describe characteristics of persons hospitalized with severe influenza illness. The rates provided are likely to be an underestimate as influenza-related 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, 2013 and January 11, 2014, 3,745 laboratory-confirmed influenza-associated hospitalizations were reported. This is a rate of 13.8 per 100,000 population. The highest hospitalization rate is among adults aged ≥65 years, followed by those in age groups 0-4 years and 50-64 years. However, those aged 18-64 years still account for 61% of reported hospitalized cases. Among all hospitalizations, 3,583 (95.7%) were influenza A, 134 (3.6%) were influenza B, 12 (0.3%) were influenza A and B co-infection, and 16 (0.4%) had no virus type information. Among those with influenza A subtype information, 22 (1.5%) were H3 and 1,433 (98.5 %) were 2009 H1N1. The most commonly reported underlying medical conditions among adults were obesity, metabolic disorders, cardiovascular disease, and asthma. The most commonly reported underlying medical conditions in children were asthma, obesity, neurologic disorders, and cardiovascular disease. Approximately 40% of hospitalized children had no identified underlying medical conditions. Among 125 hospitalized women of childbearing age (15-44 years), 27 (21.6%) were pregnant.

Additional FluSurv-NET data can be found at: and

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Outpatient Illness Surveillance

Nationwide during week 2, 3.6% 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 above the national baseline of 2.0%. (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
View National and Regional Level Graphs and Data | View Chart Data | View Full Screen | View PowerPoint Presentation

On a regional level, the percentage of outpatient visits for ILI ranged from 1.8% to 6.8% during week 2. All 10 regions reported a proportion of outpatient visits for ILI above their region-specific baseline level.

Region specific data is available at

ILINet 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 weeks with little or no influenza virus circulation. Activity levels range from minimal, which would correspond to ILI activity from outpatient clinics being below, or only slightly above, the average, to high, which would correspond to ILI activity from outpatient clinics being much higher than average.

During week 2, the following ILI activity levels were experienced:

  • Fourteen states experienced high ILI activity (Alabama, Arkansas, Idaho, Kansas, Louisiana, Mississippi, Missouri, Nevada, New Mexico, Oklahoma, Oregon, Tennessee, Texas, and Virginia).
  • Twelve states experienced moderate ILI activity (Alaska, California, Colorado, Illinois, Indiana, Kentucky, Minnesota, North Carolina, South Carolina, Utah, Vermont, and Washington).
  • Eight states and New York City experienced low ILI activity (Delaware, Florida, Hawaii, New Jersey, Pennsylvania, South Dakota, West Virginia, and Wisconsin).
  • Sixteen states experienced minimal ILI activity (Arizona, Connecticut, Georgia, Iowa, Maine, Maryland, Massachusetts, Michigan, Montana, Nebraska, New Hampshire, New York, North Dakota, Ohio, Rhode Island, 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 is 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 severity of influenza activity.

During week 2, the following influenza activity was reported:

  • Widespread influenza activity was reported by 40 states (Alaska, Arkansas, California, Colorado, Connecticut, Delaware, Georgia, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Dakota, Tennessee, Texas, Utah, Virginia, Washington, West Virginia, Wisconsin, and Wyoming).
  • Regional influenza activity was reported by Guam and nine states (Alabama, Arizona, Florida, Iowa, Massachusetts, Mississippi, New Hampshire, South Carolina, and Vermont.
  • Local influenza activity was reported the District of Columbia and Puerto Rico.
  • Sporadic influenza activity was reported by one state (Hawaii).
  • The U.S. Virgin Islands 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

FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics. To access these tools visit

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

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

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

WHO Collaborating Centers for Influenza located in Australia, China, Japan, and the United Kingdom.

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

Health Protection Agency (United Kingdom): The most up-to-date influenza information from the United Kingdom is available at

Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.


A description of surveillance methods is available at:

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