Weekly U.S. Influenza Surveillance Report

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Key Updates for Week 41, ending October 12, 2019

According to this week’s FluView report, seasonal influenza activity remains low in the United States.

Viruses

Severe Disease

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

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.

Key Messages from CDC

  • CDC expects flu activity to increase in the coming weeks.
  • An annual flu vaccine is the best way to protect against influenza and its potentially serious complications.
  • CDC recommends everyone 6 months or older get a flu vaccine by the end of October.
  • Flu antiviral drugs are prescription medications that can be used to treat flu illness, and they work best when used early (within two days of getting sick).

U.S. Virologic Surveillance

The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percent of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

Clinical Laboratories Week 41 Data Cumulative since
September 29, 2019 (week 40)
No. of specimens tested 16,672 34,990
No. of positive specimens (%) 573 (3.4%) 1,075 (3.1%)
Positive specimens by type    
    Influenza A 150 (26.2%) 311 (28.9%)
    Influenza B 423 (73.8%) 764 (71.1%)

INFLUENZA Virus Isolated
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The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.

Public Health Laboratories Week 41 Data Cumulative since
September 29, 2019 (week 40)
No. of specimens tested 407 1,029
No. of positive specimens* 64 176
Positive specimens by type/subtype    
         Influenza A 44 (68.8%) 119 (67.6%)
            (H1N1)pdm09 9 (24.3%) 24 (27.3%)
             H3N2 28 (75.7%) 64 (72.7%)
             Subtyping not performed 7 31
        Influenza B 20 (31.3%) 57 (32.4%)
            Yamagata lineage 2 (16.7%) 3 (7.5%)
            Victoria lineage 10 (83.3%) 37 (92.5%)
            Lineage not performed 8 17

INFLUENZA Virus Isolated
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Additional virologic surveillance information for this season and past seasons:
Surveillance methods - https://www.cdc.gov/flu/weekly/overview.htm#anchor_1539281228772
National, regional and state data - http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html
Age group data - http://gis.cdc.gov/grasp/fluview/flu_by_age_virus.html


Influenza Virus Characterization

CDC performs genetic and antigenic characterization of U.S. viruses submitted from state and local health laboratories using Right Size Roadmap submission guidance. These data are used to compare how similar the currently circulating influenza viruses are to the reference viruses used for developing new influenza vaccines and to monitor evolutionary changes that continually occur in influenza viruses circulating in humans. CDC also tests susceptibility of influenza viruses to antiviral medications including the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir) and the PA endonuclease inhibitor baloxavir.

Virus characterization data will be updated starting later this season when sufficient numbers of specimens have been tested.

Outpatient Illness Surveillance

Nationwide during week 41, 1.5% 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%.

national levels of ILI and ARI
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On a regional level, the percentage of outpatient visits for ILI ranged from 1.0% to 2.6% during week 41. All regions reported a percentage of outpatient visits for ILI below their region-specific baselines.


Data collected in ILINet are used to produce a measure of ILI activity* by state. During week 41, the following ILI activity levels were experienced:

  • High – 1 state (Louisiana)
  • Low – U.S. Virgin Islands
  • Minimal – District of Columbia, New York City, Puerto Rico and 49 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, 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)

*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. 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.

Additional information about medically attended visits for ILI this season and past:
Surveillance methods - https://www.cdc.gov/flu/weekly/overview.htm#anchor_1571167821424
National, regional and state data - http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html
ILI Activity Indicator Map for past weeks - https://gis.cdc.gov/grasp/fluview/main.html



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 41 the following influenza activity was reported:

  • Regional – one state (Louisiana)
  • Local – three states (California, Kentucky and Nevada).
  • Sporadic – the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 43 states (Alabama, Alaska, Arizona, Arkansas, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin and Wyoming).
  • No activity – three states (Mississippi, New Hampshire and Rhode Island).
  • Guam did not report.

Additional information about the geographic spread of influenza this season and past seasons:
Surveillance methods - https://www.cdc.gov/flu/weekly/overview.htm#anchor_1568388833450m
Map for past weeks - https://gis.cdc.gov/grasp/fluview/FluView8.html

Influenza-Associated Hospitalizations

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts 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 when a sufficient number of hospitalizations have been reported.  

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.


Pneumonia and Influenza (P&I) Mortality Surveillance

Based on National Center for Health Statistics (NCHS) mortality surveillance data available on October 17, 2019, 4.7% of the deaths occurring during the week ending October 5, 2019 (week 40) were due to P&I. This percentage is below the epidemic threshold of 5.7% for week 40.

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

Additional pneumonia and influenza mortality surveillance information for current and past seasons:
Surveillance methods - https://www.cdc.gov/flu/weekly/overview.htm#anchor_1539281356004
National, regional and state data - https://gis.cdc.gov/grasp/fluview/mortality.html
Age group data- https://gis.cdc.gov/grasp/fluview/mortality.html



Influenza-Associated Pediatric Mortality

No influenza-associated pediatric deaths were reported to CDC during week 41.

No influenza-associated pediatric deaths occurring during the 2019-2020 season have been reported.

Click on image to launch interactive tool

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Additional Influenza-associated pediatric mortality surveillance information for current and past seasons:
Surveillance methods - https://www.cdc.gov/flu/weekly/overview.htm#anchor_1571168571051
Basic demographics, underlying conditions, bacterial co-infections, and place of death for the current and past seasons - https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html



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

National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH at https://www.cdc.gov/niosh/topics/absences/default.html

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

Puerto Rico

Virgin Islands



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 and the European Centre for Disease Prevention and Control at http://www.flunewseurope.org/.

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.

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