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Situation Update: Summary of Weekly FluView Report

FluView Activity Update (Key Flu Indicators)

While influenza-like-illness (ILI) levels fell in the latest FluView report, overall influenza activity remains high across much of the United States. ILI dropped from 7.4 % last week to 6.4%, but remains higher than the peak of flu activity observed during many seasons. All U.S. states but Hawaii and Oregon continue to report widespread flu activity and 39 states plus New York City, the District of Columbia and Puerto Rico continue to report high influenza-like illness (ILI) activity. The overall hospitalization rate is higher than the end-of-season hospitalization rate for 2014-2015; a high severity, H3N2-predominant season. CDC also is reporting an additional 13 flu-related pediatric deaths during week 7, bringing the total number of flu-related pediatric deaths reported this season to 97. Flu activity is likely to remain elevated for several more weeks.

CDC continues to recommend influenza vaccination for all persons 6 months of age and older as flu viruses are likely to continue circulating for weeks and there is an increasing proportion of influenza B and H1N1 viruses being detected. Early estimates show that flu vaccine has reduced risk of having to go to the doctor due to flu by 36% overall so far this season and that flu vaccine is offering substantial protection against H1N1 flu as well as moderate protection against flu B viruses. In addition, in the context of widespread influenza activity, CDC is reminding clinicians and the public about the importance of prompt treatment with antiviral medications in people who are severely ill and people who are at high risk of serious flu complications who develop flu symptoms. Below is a summary of the key flu indicators for the week ending February 17, 2018 (week 7):

  • Influenza-like Illness Surveillance: For the week ending February 17, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 6.4%, which is a decrease from last week, but still above the national baseline of 2.2%. All 10 regions reported a proportion of outpatient visits for ILI at or above their region-specific baseline levels. ILI has been at or above the national baseline for 13 weeks so far this season. Over the past five seasons, ILI has remained at or above baseline for 16 weeks on average.
  • Influenza-like Illness State Activity Indicator Map: New York City, the District of Columbia, Puerto Rico and 39 states experienced high ILI activity (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Delaware, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, and Wyoming). Five states (Connecticut, Hawaii, Iowa, Utah, and Wisconsin) experienced moderate ILI activity. Three states experienced low ILI activity (Florida, Idaho, and Washington). Three states experienced minimal ILI activity (Maine, Montana, and North Dakota).
  • Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by Puerto Rico and 48 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, 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, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming). Local influenza activity was reported by the District of Columbia, Guam and two states (Hawaii and Oregon). No flu activity was reported by the U.S. Virgin Islands. Geographic spread data show how many areas within a state or territory are seeing flu activity.
  • Flu-Associated Hospitalizations: Since October 1, 2017, 21,279 laboratory-confirmed influenza-associated hospitalizations have been reported through the Influenza Hospitalization Network (FluSurv-NET), a population-based surveillance network for laboratory-confirmed influenza-associated hospitalizations. This translates to a cumulative overall rate of 74.5 hospitalizations per 100,000 people in the United States.
    • The highest hospitalization rate is among people 65 years and older (322.7 per 100,000), followed by adults aged 50-64 years (79.9 per 100,000), and younger children aged 0-4 years (52.6 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates, followed by children 0-4 years.
    • These rates are higher than the end-of-season rates for the 2014-2015 season. For that season, overall hospitalization was 64.2 per 100,000; hospitalization rates for people 65 years and older were 308.8 per 100,000. The hospitalization rate for people 50-64 years was 53.4 per 100,000. The hospitalization rate for children 0-4 years were 57.3 per 100,000.
    • Hospitalization data are collected from 13 states and represent approximately 9% of the total U.S. population. The number of hospitalizations reported does not reflect the actual total number of influenza-associated hospitalizations in the United States. Additional data, including hospitalization rates during other influenza seasons, can be found at http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.
  • Mortality Surveillance:
    • The proportion of deaths attributed to pneumonia and influenza (P&I) decreased but is high again at 9.5% for the week ending February 3, 2018 (week 5). This percentage is above the epidemic threshold of 7.4% for week 5 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
    • NCHS data is delayed for two weeks to allow for the collection of enough data to produce stable P&I percentages.
    • Region and state-specific data are available at https://gis.cdc.gov/grasp/fluview/mortality.html.
  • Pediatric Deaths:
    • 13 influenza-associated pediatric deaths were reported to CDC during week 7.
      • Two deaths were associated with an influenza A(H3) virus and occurred during weeks 2 and 3 (the weeks ending January 13 and January 20, 2018, respectively).  Three deaths were associated with an influenza A(H1N1)pdm09 virus and occurred during weeks 5 and 7 (the weeks ending February 3 and February 17, 2018, respectively).  Three deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 1, 4 and 7 (the weeks ending January 6, January 27, and February 17, 2018, respectively).  Four deaths were associated with an influenza B virus and occurred during weeks 6 and 7 (the weeks ending February 10 and February 17, 2018, respectively).  One death was associated with an influenza virus for which type was not determined and occurred during week 4 (the week ending January 27, 2018).
    • A total of 97 influenza-associated pediatric deaths for the 2017-2018 flu season have been reported to CDC.
  • Laboratory Data:
    • Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending February 17 was 25.4%.
    • Regionally, the three-week average percent of specimens testing positive for influenza in clinical laboratories ranged from 14.1% to 31.9%.
    • During the week ending February 17, of the 13,730 (25.4%) influenza-positive tests reported to CDC by clinical laboratories, 7,987 (58.2%) were influenza A viruses and 5,743 (41.8%) were influenza B viruses.
    • The most frequently identified influenza virus subtype reported by public health laboratories was influenza A(H3N2) virus.
    • During the week ending February 17, 636 (64.6%) of the 985 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 349 (35.4%) were influenza B viruses. Of the 612 influenza A viruses that were subtyped, 469 (76.6%) were H3N2 viruses and 143 (23.4%) were (H1N1)pdm09 viruses.
    • The majority of the influenza viruses collected from the United States during October 1, 2017 through February 17, 2018 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses.
    • Since October 1, 2017, CDC has tested 467 influenza A(H1N1)pdm09, 1,047 influenza A(H3N2), and 442 influenza B viruses for resistance to antiviral medications (i.e. oseltamivir, zanamivir, or peramivir). While the majority of the tested viruses showed susceptibility to the antiviral drugs, four (0.9%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but was sensitive to zanamivir.

FluView is available – and past issues are archived – on the CDC website.

Note: Delays in reporting may mean that data changes over time. The most up to date data for all weeks during the 2017-2018 season can be found on the current FluView and FluView Interactive.

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