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Situation Update: Summary of Weekly FluView Report

FluView Activity Update (Key Flu Indicators)

According to this week’s FluView report, influenza activity continues to decrease as the 2018-2019 season winds down, with levels of influenza-like-illness (ILI) dropping further to 1.5%. While no states reported widespread flu activity, another three flu-related pediatric deaths were reported to CDC this week, bringing the total of number of flu-related deaths in children this season 109.

Sporadic influenza activity may continue for a number of weeks. CDC continues to recommend early antiviral treatment in people with flu symptoms who are very sick or who are at high risk of developing serious flu illness.

Below is a summary of the key flu indicators for the week ending May 11, 2019:

  • Influenza-like Illness Surveillance: For the week ending May 11 (week 19), the proportion of people seeing a health care provider for influenza-like illness (ILI) decreased to 1.5% from 1.6% last week, which is below the national baseline of 2.2%. The most recent data indicate that ILI activity for the current season peaked the week ending February 16 (week 7) at 5.1%.
    • This week all ten regions reported ILI activity below their region-specific baseline levels.For the past five flu seasons, the peak percent of visits due to ILI has ranged between 3.6% (2015-2016) and 7.5% (2017-2018).
    • Additional ILINet data, including national, regional, and select state-level data for the current and previous seasons, can be found at  http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.
  • Influenza-like Illness (ILI) State Activity Indicator Map: No jurisdictions experienced high or moderate ILI activity this week. Additional data, including data for previous seasons, can be found at https://gis.cdc.gov/grasp/fluview/main.html.
  • Geographic Spread of Influenza Viruses: The number of jurisdictions reporting widespread influenza activity decreased from two last week to zero this week. However, Puerto Rico and four states reported regional influenza activity. Geographic spread data reflect 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: Between October 1, 2018 and April 30, 2019, 18,971 laboratory-confirmed influenza-associated hospitalizations were reported through the Influenza Hospitalization Network (FluSurv-NET), a population-based surveillance network for laboratory-confirmed influenza-associated hospitalizations covering approximately 9% of the U.S. This translates to a cumulative overall rate of 65.7 hospitalizations per 100,000 people in the United States.
    • The highest hospitalization rate is among adults aged 65 years and older (221.8 per 100,000) followed by adults aged 50-64 years (81.2 per 100,000), and children younger than 5 years (73.6 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates.
      • Over the past 5 seasons, cumulative end-of-season hospitalization rates have ranged from 31.4 per 100,000 (2015-2016) to 102.9 per 100,000 (2017-2018).
    • Additional data, including hospitalization rates during previous influenza seasons, can be found at http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.
    • FluSurv-Net data is used to generate national estimates of the total numbers of flu cases, medical visits, and hospitalizations. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at https://cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm.
    • Note: CDC’s active surveillance for laboratory-confirmed hospitalizations for the 2018-2019 season (“FluSurv-NET”) concluded on April 30, 2019.
  • Mortality Surveillance: The proportion of deaths attributed to pneumonia and influenza (P&I) was 5.6% during the week ending May 4, 2019 (week 18). This percentage is below the epidemic threshold of 6.7% for week 18 in the National Center for Health Statistics (NCHS) Mortality Surveillance System. P&I mortality has been at or above threshold for a total of 10 weeks this season.
    • For comparison purposes, over the last five seasons, P&I has been at or above epidemic threshold for a range of four weeks (2015-2016) to 16 weeks (2017-2018).
  • Pediatric Deaths: Three influenza-associated pediatric deaths were reported to CDC during the week ending May 11, 2019.
    • Two deaths were associated with influenza A(H1N1)pdm09 viruses and occurred during weeks 13 and 18 (the weeks ending March 30 and May 4, 2019, respectively). One death was associated with influenza A viruses for which no subtyping was performed and occurred during week 18 (the week May 4, 2019).
    • A total of 109 influenza-associated pediatric deaths have been reported for the 2018-2019 season.
    • Additional information on influenza-associated pediatric deaths reported during past seasons, including basic demographics, underlying conditions, bacterial co-infections, and place of death 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 4 was 3.7%, a decrease from 4.7% the prior week.
    • For comparison purposes, since laboratory data from clinical and public health laboratories was separated three seasons ago, the peak percent of respiratory specimens testing positive for flu at clinical laboratories has ranged from 23.6% to 27.4%.
    • This season, the percent of respiratory specimens testing positive for influenza viruses in clinical laboratories peaked during week 8 (the week ending February 23, 2019) at 26.3%.
    • Nationally, during the week ending May 11, 2019, influenza A(H3) viruses were reported more frequently than influenza A(H1N1)pdm09 viruses and were predominant in all 10 regions.
      • However, overall for the 2018-2019 flu season, influenza A(H1N1)pdm09 viruses remain predominant nationally.
    • The majority of A(H1N1)pdm09, B/Victoria and B/Yamagata influenza viruses collected in the United States during September 30, 2018 through May 11, 2019, are characterized antigenically and genetically as being similar to their cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses; however, the majority of influenza A(H3) viruses are antigenically distinguishable from A/Singapore/INFIMH-16-0019/2016 (3C.2a1), a cell-propagated reference virus representing the A(H3N2) component of 2018-19 Northern Hemisphere influenza vaccines.
    • The vast majority (>99%) of influenza viruses tested showed susceptibility to oseltamivir, zanamivir and peramivir. So far this season, four (0.1%) influenza A(H1N1)pdm09 viruses displayed highly reduced inhibition by oseltamivir and peramivir. An additional two (0.1%) influenza A(H1N1)pdm09 viruses showed reduced inhibition by oseltamivir. All influenza viruses tested showed susceptibility 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 2018-2019 season can be found on the current FluView and FluView Interactive.
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