Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content

Weekly U.S. Influenza Surveillance Report

 

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

2014-2015 Influenza Season Week 14 ending April 11, 2015


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

Synopsis:

During week 14 (April 5-11, 2015), influenza activity continued to decrease in the United States.

  • Viral Surveillance: Of 11,189 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 14, 1,076 (9.6%) were positive for influenza.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.
  • Influenza-associated Pediatric Deaths: No influenza-associated pediatric deaths were reported.
  • Influenza-associated Hospitalizations: A cumulative rate for the season of 62.4 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 1.8%, which is below the national baseline of 2.0%. Three regions reported ILI at or above region-specific baseline levels. Puerto Rico and six states experienced low ILI activity; New York City and 44 states experienced minimal ILI activity; and the District of Columbia and the U.S. Virgin Islands had insufficient data.
  • Geographic Spread of Influenza: The geographic spread of influenza in three states was reported as widespread; Guam and 14 states reported regional activity; the District of Columbia and 19 states reported local activity; and Puerto Rico, the U.S. Virgin Islands, and 14 states reported sporadic activity.

National and Regional Summary of Select Surveillance Components

HHS Surveillance Regions* Data for Current Week Data Cumulative Since September 28, 2014 (Week 40)
Out-patient ILI† Number of jurisdictions reporting regional or widespread activity§ % Respiratory specimens positive for flu‡ A(H1N1)pdm09 A (H3) A(Subtyping not performed) B Pediatric Deaths
Nation Normal 18 of 54 9.6% 212 51,408 51,431 16,560 125
Region 1 Elevated 5 of 6 14.6% 11 2,938 2,892 699 3
Region 2 Elevated 2 of 4 13.3% 56 4,101 5,257 1,330 7
Region 3 Normal 1 of 6 9.4% 9 6,200 4,814 950 10
Region 4 Normal 0 of 8 6.1% 10 3,688 12,514 3,508 22
Region 5 Elevated 3 of 6 17.7% 16 8,327 7,948 2,944 25
Region 6 Normal 1 of 5 5.8% 29 5,232 8,013 2,974 26
Region 7 Normal 0 of 4 11.0% 10 1,781 2,460 1,012 7
Region 8 Normal 2 of 6 8.7% 27 5,792 3,433 1,589 10
Region 9 Normal 2 of 5 8.3% 33 9,126 3,383 1,153 14
Region 10 Normal 2 of 4 6.0% 11 4,223 717 401 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
§ Includes all 50 states, the District of Columbia, Guam, Puerto Rico, and U.S. Virgin Islands
‡ National data are for current week; regional data are for the most recent three weeks


U.S. Virologic Surveillance:

WHO and NREVSS collaborating laboratories located in all 50 states, Puerto Rico, and the District of Columbia 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 and totals for the influenza season to date are summarized in the table below. Region specific data are available at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.

 

Week 14

Data Cumulative
since September 28, 2014
(Week 40)

No. of specimens tested

11,189

623,177

No. of positive specimens (%)

1,076 (9.6%)

119,612 (19.2%)

Positive specimens by type/subtype

   

  Influenza A

139 (12.9%)

103,052 (86.2%)

            A(H1N1)pdm09

3 (2.2%)

212 (0.2%)

            H3

46 (33.1%)

51,408 (49.9%)

            Subytping not performed

90 (64.7%)

51,431 (49.9%)

  Influenza B

937 (87.1%)

16,560 (13.8%)

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

Since the start of the season, influenza A (H3N2) viruses have predominated nationally; however since early March, the proportion of influenza B viruses has been increasing. During week 14, 87% of all influenza positive specimens reported were influenza B viruses, and influenza B viruses predominated in all 10 regions.



Influenza Virus Characterization*:

CDC has characterized 1,600 influenza viruses [39 A(H1N1)pdm09, 1,102 A(H3N2), and 459 influenza B viruses] collected by U.S. laboratories since October 1, 2014.

Influenza A Virus [1,141]

  • A (H1N1)pdm09 [39]: All 39 H1N1 viruses tested were characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2014-2015 Northern Hemisphere influenza vaccine.
  • A (H3N2) [1,102]: 243 (22.1%) of the 1,102 H3N2 viruses tested have been characterized as A/Texas/50/2012-like, the influenza A (H3N2) component of the 2014-2015 Northern Hemisphere influenza vaccine. 859 (77.9%) of the 1,102 viruses tested showed either reduced titers with antiserum produced against A/Texas/50/2012 or belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012. Among viruses that showed reduced titers with antiserum raised against A/Texas/50/2012, most were antigenically similar to A/Switzerland/9715293/2013, the H3N2 virus selected for the 2015 Southern Hemisphere influenza vaccine. A/Switzerland/9715293/2013 is related to, but antigenically and genetically distinguishable from, the A/Texas/50/2012 vaccine virus. A/Switzerland-like H3N2 viruses were first detected in the United States in small numbers in March of 2014 and began to increase through the spring and summer.

Influenza B Virus [459]

332 (72.3%) of the influenza B viruses tested belong to B/Yamagata/16/88 lineage and the remaining 127 (27.7%) influenza B viruses tested belong to B/Victoria/02/87 lineage.

  • Yamagata Lineage [332]: 321 (96.7%) of the 332 B/Yamagata-lineage viruses were characterized as B/Massachusetts/2/2012-like, which is included as an influenza B component of the 2014-2015 Northern Hemisphere trivalent and quadrivalent influenza vaccines. Eleven (3.3%) of the B/Yamagata-lineage viruses tested showed reduced titers to B/Massachusetts/2/2012.
  • Victoria Lineage [127]: 122 (96.1%) of the 127 B/Victoria-lineage viruses were characterized as B/Brisbane/60/2008-like, the virus that is included as an influenza B component of the 2014-2015 Northern Hemisphere quadrivalent influenza vaccine. Five (3.9%) of the B/Victoria-lineage viruses tested showed reduced titers to B/Brisbane/60/2008.

*CDC routinely uses hemagglutination inhibition (HI) assays to antigenically characterize influenza viruses year-round to compare how similar currently circulating influenza viruses are to those included in the influenza vaccine, and to monitor for changes in circulating influenza viruses. However, a portion of recent influenza A(H3N2) viruses do not grow to sufficient hemagglutination titers for antigenic characterization by HI. For many of these viruses, CDC is also performing genetic characterization to infer antigenic properties.


2015-2016 Influenza Season – U.S. Influenza Vaccine Composition:

The World Health Organization (WHO) has recommended vaccine viruses for the 2015-2016 influenza season Northern Hemisphere vaccine composition, and the Food and Drug Administration’s Vaccines and Related Biological Products Advisory Committee (VRBPAC) has made the vaccine composition recommendation to be used in the United States. Both agencies recommend that trivalent vaccines contain an A/California/7/2009 (H1N1)pdm09-like virus, an A/Switzerland/9715293/2013 (H3N2)-like virus, and a B/Phuket/3073/2013-like (B/Yamagata lineage) virus. It is recommended that quadrivalent vaccines, which have two influenza B viruses, contain the viruses recommended for the trivalent vaccines, as well as a B/Brisbane/60/2008-like (B/Victoria lineage) virus. This represents a change in the influenza A (H3) and influenza B (Yamagata lineage) components compared with the composition of the 2014-2015 influenza vaccine. These vaccine recommendations were based on several factors, including global influenza virologic and epidemiologic surveillance, genetic characterization, antigenic characterization, antiviral resistance, and the candidate vaccine viruses that are available for production.


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, 2014

 

Oseltamivir

Zanamivir

Peramivir

 

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

47

1 (2.1)

42

0 (0.0)

47

1 (2.1)

Influenza A (H3N2)

2,709

0 (0.0)

2,709

0 (0.0)

1,513

0 (0.0)

Influenza B

512

0 (0.0)

512

0 (0.0)

512

0 (0.0)


In the United States, the vast majority of recently circulating influenza viruses have been susceptible to the neuraminidase inhibitor antiviral medications, oseltamivir, zanamivir, and peramivir; rare sporadic instances of oseltamivir-resistant A(H1N1)pdm09 and A(H3N2) viruses have been detected worldwide. Antiviral treatment 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 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:

During week 14, 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 7.0% for week 14.

Pneumonia And Influenza Mortality
View Full Screen | View PowerPoint Presentation


For the 2014-2015 influenza season, CDC/Influenza Division and the National Center for Health Statistics (NCHS) are collaborating on a pilot project to use NCHS mortality surveillance data for the rapid assessment of pneumonia and influenza (P&I) mortality. To view the data, please click here.



Influenza-Associated Pediatric Mortality:

No influenza-associated pediatric deaths were reported to CDC during week 14.

A total of 125 influenza-associated pediatric deaths have been reported during the 2014-2015 season from New York City [3] and 38 states (Arizona [3], Arkansas [4], California [3], Colorado [6], Florida [3], Georgia [1], Illinois [3], Indiana [1], Iowa [3], Kansas [2], Kentucky [3], Louisiana [2], Maryland [1], Massachusetts [1], Michigan [1], Minnesota [8], Mississippi [1], Missouri [1], Nebraska [1], Nevada [8], New Jersey [1], New Mexico [1], New York [3], North Carolina [2], Ohio [6], Oklahoma [6], Pennsylvania [3], Rhode Island [2], South Carolina [3], South Dakota [1], Tennessee [9], Texas [13], Utah [2], Virginia [5], Washington [1], Wisconsin [6], West Virginia [1], and Wyoming [1]).

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

Click on image to launch interactive tool

View Interactive Application | View Full Screen | View PowerPoint Presentation




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, and 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 and 2014-2015 seasons.

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, 2014 and April 11, 2015, 17,065 laboratory-confirmed influenza-associated hospitalizations were reported. The overall hospitalization rate was 62.4 per 100,000 population. The highest rate of hospitalization was among adults aged ≥65 years (308.0 per 100,000 population), followed by children aged 0-4 years (54.4 per 100,000 population). Among all hospitalizations, 15,014 (87.9%) were associated with influenza A, 1,855 (10.9%) with influenza B, 88 (0.5%) with influenza A and B co-infection, and 108 (0.6%) had no virus type information. Among those with influenza A subtype information, 5,091 (99.7%) were A(H3N2) and 12 (0.3%) were A(H1N1)pdm09.

Clinical findings are preliminary and based on 6,231 (36.5%) cases with complete medical chart abstraction. The majority (93.7%) of hospitalized adults had at least one reported underlying medical condition; the most commonly reported were cardiovascular disease, metabolic disorders, and obesity. There were 784 hospitalized children with complete medical chart abstraction, 327 (41.7%) had no identified underlying medical conditions. The most commonly reported underlying medical conditions among pediatric patients were asthma, neurologic disorders, and obesity. Among the 469 hospitalized women of childbearing age (15-44 years), 154 (32.8%) were pregnant.

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.


Click on graph to launch interactive tool

Data from the Influenza Hospitalization Surveillance Network (FluSurv-NET), a population-based surveillance for influenza related hospitalizations in children and adults in 13 U.S. states. Cumulative incidence rates are calculated using the National Center for Health Statistics’ (NCHS) population estimates for the counties included in the surveillance catchment area.

View Interactive Application | View Full Screen | View PowerPoint Presentation


Click on graph to launch interactive tool2

FluSurv-NET data are preliminary and displayed as they become available. Therefore, figures are based on varying denominators as some variables represent information that may require more time to be collected. Data are refreshed and updated weekly. Asthma includes a medical diagnosis of asthma or reactive airway disease; Cardiovascular diseases include conditions such as coronary heart disease, cardiac valve disorders, congestive heart failure, and pulmonary hypertension; does not include isolated hypertension; Chronic lung diseases include conditions such as chronic obstructive pulmonary disease, bronchiolitis obliterans, chronic aspiration pneumonia, and interstitial lung disease; Immune suppression includes conditions such as immunoglobulin deficiency, leukemia, lymphoma, HIV/AIDS, and individuals taking immunosuppressive medications; Metabolic disorders include conditions such as diabetes mellitus; Neurologic diseases include conditions such as seizure disorders, cerebral palsy, and cognitive dysfunction; Neuromuscular diseases include conditions such as multiple sclerosis and muscular dystrophy; Obesity was assigned if indicated in patient's medical chart or if body mass index (BMI) >30 kg/m2; Pregnancy percentage calculated using number of female cases aged between 15 and 44 years of age as the denominator; Renal diseases include conditions such as acute or chronic renal failure, nephrotic syndrome, glomerulonephritis, and impaired creatinine clearance; No known condition indicates that the case did not have any known high risk medical condition indicated in medical chart at the time of hospitalization.

View Interactive Application | View Full Screen | View PowerPoint Presentation




Outpatient Illness Surveillance:

Nationwide during week 14, 1.8% 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 2.0%.

(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
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 0.7% to 2.9% during week 14. Three regions (Regions 1, 2, and 5) 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 14, the following ILI activity levels were calculated:

  • Puerto Rico and six states (Connecticut, Hawaii, Illinois, Oklahoma, Texas, and Vermont) experienced low ILI activity.
  • New York City and 44 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Delaware, Florida, Georgia, Idaho, 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, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Utah, Virginia, Washington, West Virginia, Wisconsin, and Wyoming) experienced minimal ILI activity.
  • Data were insufficient to calculate an ILI activity level from the District of Columbia and the U.S. Virgin Islands.

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 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 14, the following influenza activity was reported:

  • Three states (Connecticut, Massachusetts, and New York) reported widespread influenza activity.
  • Guam and 14 states (Hawaii, Illinois, Maine, Maryland, Michigan, Montana, New Hampshire, New Jersey, North Dakota, Ohio, Oklahoma, Oregon, Vermont, and Washington) reported regional influenza activity.
  • The District of Columbia and 19 states (Arizona, Colorado, Delaware, Florida, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Missouri, Nebraska, New Mexico, Rhode Island, South Carolina, Texas, Utah, Virginia, Wisconsin, and Wyoming) reported local activity.
  • Puerto Rico, the U.S. Virgin Islands, and 14 states (Alabama, Alaska, Arkansas, California, Georgia, Idaho, Kansas, Mississippi, Nevada, North Carolina, Pennsylvania, South Dakota, Tennessee, and West Virginia) reported sporadic activity.

U. S. Map for Weekly Influenza Activity

Flu Activity data in XML Format | View Full Screen





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.

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

Puerto Rico



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 United States and worldwide, see http://www.google.org/flutrends/

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.

In addition to the eight data components of CDC influenza surveillance for the 2014-2015 influenza season, the use of National Center for Health Statistics (NCHS) pneumonia and influenza mortality surveillance data for the rapid assessment of influenza-associated mortality will be piloted. An overview of influenza surveillance, including a description of the NCHS mortality surveillance data, is available here.

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

Top