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Situation Update: Summary of Weekly FluView Report

Key Flu Indicators

According to the FluView report for the week ending February 18, 2017 (week 7), flu activity decreased slightly but remained elevated nationally. Also, CDC reported five additional flu-associated pediatric deaths for the 2016-2017 season. The proportion of people seeing their health care provider for influenza-like-illness (ILI) has been at or above the national baseline for ten consecutive weeks so far this season. Influenza A (H3N2) viruses continue to predominate. Based on early estimates, flu vaccines this season have 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. Anyone who has not gotten vaccinated yet this season should get vaccinated now. Below is a summary of the key flu indicators for the week ending February 18, 2017:

  • Influenza-like Illness Surveillance: For the week ending February 18, the proportion of people seeing their health care provider for influenza-like illness (ILI) decreased to 4.8%. This remains above the national baseline of 2.2%. Nine regions (Regions 1, 2, 3, 4, 5, 6, 7, 8, and 10) reported ILI at or above their region-specific baseline level. 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.
  • Influenza-like Illness State Activity Indicator Map: 27 states (Alabama, Alaska, Arkansas, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, New Jersey New Mexico, New York, North Carolina, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Virginia, and Wyoming) experienced high ILI activity. New York City and 5 states (Connecticut, Iowa, Nebraska, North Dakota, and Ohio) experienced moderate ILI activity.  Puerto Rico and 10 states (Arizona, California, Florida, Hawaii, Idaho, Massachusetts, New Hampshire, Oregon, West Virginia, and Wisconsin) experienced low ILI activity. Eight states (Colorado, Delaware, Maine, Montana, Nevada, Utah, Vermont, and Washington) 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.
  • Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by Puerto Rico and 44 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, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Texas, Vermont, Virginia, West Virginia, Wisconsin, and Wyoming).  Regional influenza activity was reported by Guam and four states (Montana, Oregon, Tennessee, and Washington). Local influenza activity was reported by the District of Columbia and one state (Hawaii). Sporadic influenza activity was reported by one state (Utah).  No influenza 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, 2016, a total of 9,444 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative overall rate of 33.7 hospitalizations per 100,000 people in the United States. This is lower than the hospitalization rate at this time (36.9 per 100,000) during the 2012-2013 flu season, when influenza A H3N2 viruses also predominated.
    • The 2012-2013 flu season was a recent influenza A H3N2-predominant season in the United States. Influenza A (H3N2) viruses also predominated during the 2014- 2015 flu season, but more than 70% of the H3N2 viruses circulating that season were different or "drifted" from the H3N2 vaccine virus.
    • The hospitalization rate among people 65 years and older is 155.2 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 161.8 per 100,000.
    • The hospitalization rate among adults 50-64 years is 32.8 per 100,000. During 2012-2013 flu season, the hospitalization rate for that age group for the same week was 33.7 per 100,000 respectively.
    • The hospitalization rate among children younger than 5 years is 20.8 per 100,000. During 2012-2013 flu season, the hospitalization rate for people in that age group for the same week was 51.9 per 100,000 respectively.
    • During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
  • Mortality Surveillance:
    • The proportion of deaths attributed to pneumonia and influenza (P&I) was 7.8% for the week ending February 4, 2017 (week 5). This percentage is above the epidemic threshold of 7.5% for week 5 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
  • Pediatric Deaths:
    • Five influenza-associated pediatric deaths are being reported by CDC for the week ending February 18, 2017.
    • Three deaths were associated with an influenza A (H3N2) virus and occurred during weeks 4 and 6 (the weeks ending January 28 and February 11, 2017, respectively).  
    • One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 6 (the week ending February 11, 2017).  
    • One death was associated with an influenza B virus and occurred during week 6.
    • A total of 34 influenza-associated pediatric deaths have been reported for the 2016-2017 season.
    • Additional information on pediatric deaths for the 2016-2017 season is now 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 February 18 was 24.0%.
    • Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 12.7% to 30.3%.
    • During the week ending February 18, of the 8,272 (24.0%) influenza-positive tests reported to CDC by clinical laboratories, 6,506 (78.7%) were influenza A viruses and 1,766 (21.3%) were influenza B viruses.
    • The most frequently identified influenza virus type reported by public health laboratories during the week ending February 18 was influenza A viruses, with influenza A (H3N2) viruses predominating.  
    • During the week ending February 18, 1,044 (83.7%) of the 1,247 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 203 (16.3%) were influenza B viruses. Of the 1,006 influenza A viruses that were subtyped, 974 (96.8%) were H3N2 viruses and 32 (3.2%) were (H1N1)pdm09 viruses.
    • Since 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 1,260 specimens (136 influenza A (H1N1)pdm09, 836 influenza A (H3N2), and 288 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 tdate data for all weeks during the 2016-2017 season can be found on the current FluView.

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