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Situation Update: Summary of Weekly FluView Report

The May 14-20, 2017 FluView marks the final full influenza surveillance report for the 2016-2017 flu season in the United States. Influenza surveillance in the U.S. will continue through the summer months with condensed reports available at FluView; though this page will not be updated until publication of the full FluView resumes in October 2017. FluView interactive will be updated over the summer months.

FluView Activity Update (Key Flu Indicators)

According to the FluView report for the week ending May 20, 2017 (week 20), flu activity continues to decrease in the United States. The 2016-2017 flu season is winding down, however flu activity persists in some areas. While no states are reporting widespread activity at the time, two states (Arizona and Maine) and Guam continue to report regional flu activity and another 3 flu-related pediatric deaths were reported. This brings the total number of flu deaths in children reported to CDC during this season to 95. Sporadic flu activity may continue for a number of weeks. While influenza A (H3N2) viruses have been most common overall this season, influenza B viruses accounted for 68% of the viruses reported by public health laboratories during week 20. Interim vaccine effectiveness (VE) estimates indicate flu vaccines this season reduced a vaccinated person’s risk of getting sick and having to go to the doctor because of flu by about half (48%). CDC recommends annual flu vaccination for everyone 6 months of age and older. Vaccination efforts should continue for as long as influenza viruses are circulating. Below is a summary of the key flu indicators for the week ending May 20, 2017:

  • Influenza-like Illness Surveillance: For the week ending May 20 the proportion of people seeing their health care provider for influenza-like illness (ILI) was 1.3% and has now been below the national baseline of 2.2% for six consecutive weeks. All 10 regions reported a proportion of outpatient visits for ILI below their region-specific baseline levels.  For the 2016-2017 season, ILI was at or above baseline for 17 consecutive weeks. For the last 15 seasons, the average duration of a flu season by this measure has been 13 weeks, with a range from one week to 20 weeks. Additional ILINet data, including data for previous seasons, can be found at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.
  • Influenza-like Illness State Activity Indicator Map: No states experienced high or moderate ILI activity. One state (Arizona) experienced low ILI activity. New York City, Puerto Rico and 49 states (Alabama, Alaska, Arkansas, California, Colorado, Connecticut, Delaware, 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, and Wyoming) experienced minimal ILI activity. The District of Columbia did not have sufficient data to calculate an activity level. ILI activity data indicate the amount of flu-like illness that is occurring in each state. Additional data, including data for previous seasons, can be found at https://gis.cdc.gov/grasp/fluview/main.html.
  • Geographic Spread of Influenza Viruses: No states experienced widespread influenza activity. Regional influenza activity was reported by Guam and Arizona and Maine. Local influenza activity was reported by Puerto Rico and 9 states (Alaska, California, Connecticut, Louisiana, Massachusetts, New Hampshire, Ohio, South Carolina, and Washington). Sporadic activity was reported by the District of Columbia and 34 states Alabama, Arkansas, Colorado, Delaware, Florida, Georgia, Hawaii, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, North Dakota, Oklahoma, Oregon, Pennsylvania, South Dakota, Texas, Utah, Vermont, Virginia, West Virginia, Wisconsin, and Wyoming). No influenza activity was reported by the U.S. Virgin Islands and five states (Idaho, Illinois, Kansas, Rhode Island, and Tennessee). Geographic spread data show how many areas within a state or territory are seeing flu activity. Additional data are available at: https://gis.cdc.gov/grasp/fluview/FluView8.html.
  • Flu-Associated Hospitalizations: As of May 20, 2017, 18,256 laboratory-confirmed influenza-associated hospitalizations occurring between October 1, 2016, and April 30, 2017, have been reported through the Influenza Hospitalization Surveillance Network (FluSurv-NET). This translates to a cumulative overall rate of 65.2 hospitalizations per 100,000 people in the United States. This is higher than the cumulative hospitalization rate for the 2012-2013 flu season (44.0 per 100,000), when influenza A (H3N2) viruses also predominated, and is slightly higher than the cumulative hospitalization rate during 2014-2015 (64.1 per 100,000) which also was an H3N2 predominant season.
    • The hospitalization rate among people 65 years and older is 291.1 per 100,000. This is the highest rate of any age group. The hospitalization rate for people 65 and older for the same week during the 2012-2013 flu season was 183.9 per 100,000. For week 17 during 2014-2015, it was 308.8 per 100,000.
    • The hospitalization rate among adults 50-64 years is 65.1 per 100,000. This is the highest hospitalization rate ever observed for this age group since this type of surveillance began. During the 2012-2013 and 2014-2015 flu seasons, the hospitalization rate for that age group for the same week was 40.9 per 100,000 and 53.4 per 100,000 respectively.
    • The hospitalization rate among children younger than 5 years is 45.1 per 100,000. During the 2012-2013 and 2014-2015 flu seasons, the hospitalization rate for that age group for the same week was 67.0 per 100,000 and 57.2 per 100,000 respectively.
    • During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
    • 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) was 6.1% for the week ending May 6, 2017 (week 18). This percentage is below the epidemic threshold of 6.9% for week 18 in the National Center for Health Statistics (NCHS) Mortality Surveillance System. The weekly percentage of deaths attributed to P&I was at or exceeded the epidemic threshold for 12 consecutive weeks this season.
    • Region and state-specific data are available at http//gis.cdc.gov/grasp/fluview/mortality.html.
  • Pediatric Deaths:
    • Three influenza-associated pediatric deaths are being reported by CDC for the week ending May 20, 2017.
    • Two deaths were associated with an influenza A (H3) virus and occurred during weeks 51 and 16 (the weeks ending December 24, 2016, and April 22, 2017respectively).
    • One death was associated with an influenza B virus and occurred during week 18 (the week ending May 6, 2017).
    • A total of 95 influenza-associated pediatric deaths have been reported to CDC for the 2016-2017 season.
    • Additional information on pediatric deaths for the 2016-2017 season and previous seasons is available on FluView Interactive at: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.
  • Laboratory Data:
    • Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending May 20 was 4.3%.
    • Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 2.0% to 7.5%.
    • During the week ending May 20, of the 369 (4.3%) influenza-positive tests reported to CDC by clinical laboratories, 99 (26.8%) were influenza A viruses and 270 (73.2%) were influenza B viruses.
    • While influenza A (H3N2) viruses have predominated this season, the most frequently identified influenza virus type reported by public health laboratories since mid-March  has been influenza B viruses.
    • During the week ending May 20, 27 (32.1%) of the 84 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 57 (67.9%) were influenza B viruses. Of the 26 influenza A viruses that were subtyped, 24 (92.3%) were H3N2 viruses and 2 (7.7%) was a (H1N1)pdm09 virus.
    • Additional virologic data, including data for previous seasons, can be found at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html and http://gis.cdc.gov/grasp/fluview/flu_by_age_virus.html.
  • October 1, 2016, antigenic and/or genetic characterization shows that the majority of the tested viruses remain similar to the recommended components of the 2016-2017 Northern Hemisphere vaccines.
  • Since October 1, 2016, CDC tested 3,458  specimens (324 influenza A (H1N1)pdm09, 2,305 influenza A (H3N2), and 829 influenza B viruses) for resistance to the neuraminidase inhibitors antiviral drugs. None of the tested viruses were found to be resistant to oseltamivir, zanamivir, or peramivir.

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 2016-2017 season can be found on the current FluView and FluView Interactive.

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