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

2015-2016 Influenza Season Week 47 ending November 28, 2015

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


During week 47 (November 22-28, 2015), influenza activity increased slightly in the United States but remained low overall.

National and Regional Summary of Select Surveillance Components

HHS Surveillance Regions* Data for current week Data cumulative since October 4, 2015 (week 40)
Out-patient ILI Number of jurisdictions experiencing high or moderate ILI activity§ % respiratory specimens positive for flu in clinical laboratories A(H1N1)pdm09 A (H3) A (Subtyping not Performed)
B Victoria lineage B Yamagata lineage B lineage not performed Pediatric Deaths
Influenza test results from public health laboratories only
Nation Normal 3 of 53 1.5% 55 262 16 8 13 50 2
Region 1 Normal 0 of 6 0.4% 4 14 0 0 0 0 0
Region 2 Normal 1 of 4 0.4% 7 15 0 0 0 4 0
Region 3 Elevated 0 of 6 0.6% 5 13 1 0 4 0 0
Region 4 Elevated 1 of 8 3.4% 2 24 3 0 0 12 0
Region 5 Normal 0 of 6 0.8% 21 20 3 1 3 1 0
Region 6 Elevated 1 of 5 1.4% 0 14 0 1 1 6 1
Region 7 Normal 0 of 4 0.2% 1 21 0 1 1 1 0
Region 8 Normal 0 of 6 0.2% 5 14 1 2 1 0 0
Region 9 Normal 0 of 4 0.8% 9 86 7 3 3 25 1
Region 10 Normal 0 of 4 0.2% 1 41 1 0 0 1 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
§ Includes all 50 states, New York City, the District of Columbia and Puerto Rico
‡ National data are for current week; regional data are for the most recent three weeks

U.S. Virologic Surveillance:

WHO and NREVSS collaborating laboratories, which include both public health and clinical laboratories located in all 50 states, Puerto Rico, and the District of Columbia, report to CDC the total number of respiratory specimens tested for influenza and the number positive for influenza by virus type. In addition, public health laboratories also report the influenza A subtype (H1 or H3) and influenza B lineage information of the viruses they test and the age or age group of the persons from whom the specimens were collected.

Additional data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.

The results of tests performed by clinical laboratories during the current week are summarized below.

  Week 47 Data Cumulative since
October 4, 2015 (Week 40)
No. of specimens tested 11,288 102,675
No. of positive specimens (%) 171 (1.5%) 1,268 (1.2%)
Positive specimens by type    
    Influenza A 103 (60.2%) 772 (60.9%)
    Influenza B 68 (39.8%) 496 (39.1%)
INFLUENZA Virus Isolated
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The results of tests performed by public health laboratories, as well as the age group distribution of influenza positive tests, during the current week are summarized below.

  Week 47
Data Cumulative since
October 4, 2015 (Week 40)
No. of specimens tested 481 8,488
No. of positive specimens 13 404
Positive specimens by type/subtype    
    Influenza A 12 (92.3%) 333 (82.4%)
          A(H1N1)pdm09 5 (41.7%) 55 (16.5%)
          H3 7 (58.3%) 262 (78.7%)
          Subtyping not performed 0 (0%) 16 (4.8%)
    Influenza B 1 (7.7%) 71 (17.6%)
           Yamagata lineage 0 (0%) 13 (18.3%)
           Victoria lineage 0 (0%) 8 (11.3%)
           Lineage not performed 1 (100%) 50 (70.4%)
INFLUENZA Virus Isolated
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INFLUENZA Virus Isolated
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INFLUENZA Virus Isolated
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Influenza Virus Characterization:

CDC characterizes influenza viruses through one or more tests including genome sequencing, hemagglutination inhibition (HI) and/or neutralization assays. This data is used to compare how similar currently circulating influenza viruses are to the reference viruses used for developing influenza vaccines, and to monitor for changes in circulating influenza viruses. Historically, HI data has been used most commonly to assess the similarity between reference viruses and circulating viruses to suggest how well the vaccine may work until such time as vaccine effectiveness estimates are available. During the 2014–2015 season and to date, however, a portion of influenza A (H3N2) viruses do not yield sufficient hemagglutination titers for antigenic characterization by HI. For many of these viruses, CDC performs genetic characterization to determine the genetic group identity of those viruses. In this way, antigenic properties of these viruses can be inferred from viruses within the same genetic group that have been characterized antigenically.

CDC has characterized 62 influenza viruses [18 A (H1N1)pdm09, 43 A (H3N2), and 1 influenza B viruses] collected by U.S. laboratories since October 1, 2015.

Influenza A Virus [61]

Influenza B Virus [1]

Yamagata Lineage [1]: One B/Yamagata-lineage virus was antigenically characterized as B/Phuket/3073/2013-like, which is included as an influenza B component of the 2015-2016 Northern Hemisphere trivalent and quadrivalent influenza vaccines.

Victoria Lineage [0]: No B/Victoria-lineage viruses were antigenically characterized.

CDC has characterized 359 influenza viruses [17 A (H1N1)pdm09, 271 A (H3N2), and 71 influenza B virus] collected by U.S. laboratories from May 24-September 30,2015.

The 271 influenza A(H3N2) viruses collected from May 24-September 30, 2015 have been genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to A/Switzerland/9715293/2013, the influenza A (H3N2) cell-propagated reference virus representing the 2015-2016 Northern Hemisphere vaccine. Two hundred and six viruses (17 A (H1N1)pdm09, 118 A (H3N2), 44 B/Yamagata-lineage, and 27 B/Victoria-lineage) collected from May 24-September 30, 2015 have been antigenically characterized. All but one virus were similar to the reference viruses representing the 2015-2016 Northern Hemisphere influenza vaccine components.

Antiviral Resistance:

Testing of influenza A(H1N1)pdm09, A(H3N2), and influenza B virus isolates for resistance to neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) is performed at CDC using a functional assay. Additional A(H1N1)pdm09 and 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 A(H1N1)pdm09 and A(H3N2) viruses (the adamantanes are not effective against influenza B viruses). Therefore, data from adamantane resistance testing are not presented below.

Neuraminidase Inhibitor Resistance Testing Results on Samples Collected Since October 1, 2015






Virus Samples tested (n)

Resistant Viruses, Number (%)

Virus Samples tested (n)

Resistant Viruses, Number (%)

Virus Samples tested (n)

Resistant Viruses, Number (%)

Influenza A (H1N1)pdm09


0 (0.0)


0 (0.0)


0 (0.0)

Influenza A (H3N2)


0 (0.0)


0 (0.0)


0 (0.0)

Influenza B


0 (0.0)


0 (0.0)


0 (0.0)

The majority of recently circulating influenza viruses are susceptible to the neuraminidase inhibitor antiviral medications, oseltamivir, zanamivir, and peramivir; however, rare sporadic instances of oseltamivir-resistant and peramivir-resistant influenza A (H1N1)pdm09 and oseltamivir-resistant influenza A (H3N2) viruses have been detected worldwide. Antiviral treatment as early as possible is recommended for patients with confirmed or suspected influenza who have severe, complicated, or progressive illness; who require hospitalization; or who are at high risk. for serious influenza-related complications. Additional information on recommendations for treatment and chemoprophylaxis of influenza virus infection with antiviral agents is available at http://www.cdc.gov/flu/antivirals/index.htm.

Pneumonia and Influenza (P&I) Mortality Surveillance:

Rapid tracking of pneumonia and influenza-associated deaths is done through two systems, the National Center for Health Statistics (NCHS) Mortality Surveillance System and the 122 Cities Mortality Reporting System. NCHS mortality surveillance data are presented by the week the death occurred and P&I percentages are released two weeks after the week of death to allow for collection of enough data to produce a stable P&I percentage. Users of the data should not expect the two systems to produce the same percentages, and the percent P&I deaths from each system should be compared to the corresponding system-specific baselines and thresholds.

NCHS Mortality Surveillance Data:

Based on NCHS mortality surveillance data available on December 3, 2015, 5.9% of the deaths occurring during the week ending November 14, 2015 (week 45) were due to P&I. This percentage is below the epidemic threshold of 6.8% for week 45.

Region and state-specific data are available at http://www.cdc.gov/flu/weekly/nchs.htm.

INFLUENZA Virus Isolated
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122 Cities Mortality Reporting System:

During week 47, 6.1% of all deaths reported through the 122 Cities Mortality Reporting System were due to P&I. This percentage was below the epidemic threshold of 6.5% for week 47.

Pneumonia And Influenza Mortality
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Influenza-Associated Pediatric Mortality:

No influenza-associated pediatric deaths were reported to CDC during week 47. A total of two influenza-associated pediatric deaths have been reported during the 2015-2016 season.

Additional data can be found at: http://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.

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Influenza-Associated Hospitalizations:

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts all age population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in the Emerging Infections Program (EIP) states and Influenza Hospitalization Surveillance Project (IHSP) states. FluSurv-NET estimated hospitalization rates will be updated weekly starting later this season. Additional FluSurv-NET data can be found at: http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.

Outpatient Illness Surveillance:

Nationwide during week 47, 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 2.1%.

(ILI is defined as fever (temperature of 100°F [37.8°C] or greater) and cough and/or sore throat.)

Additional data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.

national levels of ILI and ARI
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On a regional level, the percentage of outpatient visits for ILI ranged from 0.6% to 4.3% during week 47. Three regions (Regions 3, 4, and 6) reported a proportion of outpatient visits for ILI at or above their 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 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 47, the following ILI activity levels were calculated:

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*This map uses the proportion of outpatient visits to health care providers for ILI 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 disproportionally 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 are 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 47, the following influenza activity was reported:

U. S. Map for Weekly Influenza Activity

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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 http://www.cdc.gov/flu/weekly/fluviewinteractive.htm.

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

Puerto Rico

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, the United Kingdom, and the United States (CDC in Atlanta, Georgia).

Europe: for the most recent influenza surveillance information from Europe, please see WHO/Europe at http://www.flunewseurope.org/ 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/

Public Health England: The most up-to-date influenza information from the United Kingdom is available at https://www.gov.uk/government/statistics/weekly-national-flu-reports

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.

An overview of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available at: http://www.cdc.gov/flu/weekly/overview.htm.