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Situation Update: Summary of Weekly FluView Report

The FluView report published on May 25 marks the final full influenza surveillance report of the 2017-2018 flu season in the United States. Influenza surveillance in the U.S. will continue through the summer months and a condensed FluView report will be available at http://www.cdc.gov/flu/weekly/ each Friday; though this page will not be updated until publication of the full FluView for the 2018-2019 season resumes on October 12, 2018. FluView Interactive will be updated over the summer months.

FluView Activity Update (Key Flu Indicators)

Influenza activity in the United States continued to decrease, and is below the national baseline for the seventh consecutive week since late November according to the latest FluView report. Influenza-like illness (ILI) decreased slightly to 1.2%. Current data indicate that the 2017-2018 flu season peaked at 7.5% in early February (during week 5). However, 2 states, Guam, and Puerto Rico continue to report widespread or regional flu activity. Hospitalization rates this season have been record-breaking, exceeding end-of-season hospitalization rates for 2014-2015, a high severity, H3N2-predominant season. CDC also is reporting an additional 1 flu-related pediatric death during week 20, bringing the total number of flu-related pediatric deaths this season to 169. Localized or sporadic flu activity may continue for a number of weeks. CDC recommends prompt treatment with influenza antiviral medications for 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 May 19, 2018 (week 20):

  • Influenza-like Illness Surveillance: For the week ending May 19, the proportion of people seeing their health care provider for influenza-like illness (ILI) decreased slightly to 1.2% and is below the national baseline of 2.2% for the seventh consecutive week since late November. All 10 regions reported a percentage of outpatient visits for ILI below their region-specific baselines. ILI was been at or above the national baseline for 19 weeks this season. Over the past five seasons, ILI has remained at or above baseline for 16 weeks on average with 20 weeks being the longest.
  • Influenza-like Illness State Activity Indicator Map: New York City, the District of Columbia, Puerto Rico and all 50 states experienced minimal ILI activity.
  • Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by one state (Massachusetts). Regional influenza activity was reported by Guam, Puerto Rico and one state (Utah). Local influenza activity was reported by seven states (Arizona, Connecticut, Maryland, New Jersey, New York, Ohio, and Wisconsin). Sporadic influenza activity was reported by the District of Columbia, the U.S. Virgin Islands, and 37 states (Alaska, Arkansas, California, Colorado, Delaware, Florida, Georgia, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Mexico, North Carolina, North Dakota, Oklahoma, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, Washington, West Virginia, and Wyoming). No influenza activity was reported by four states (Alabama, Mississippi, New Hampshire, and Rhode Island).
  • Geographic spread data show how many areas within a state or territory are seeing flu activity.
  • Flu-Associated Hospitalizations: Between October 1, 2017, and April 30, 2018, 30,451 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 106.6 hospitalizations per 100,000 people in the United States.
    • The highest hospitalization rate is among people 65 years and older (460.8 per 100,000), followed by adults aged 50-64 years (115.7 per 100,000), and younger children aged 0-4 years (74.5 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates, followed by children 0-4 years.
      • The rates reported this season are higher than the end-of-season hospitalization rates for all ages (cumulative) and all age-group specific rates for the 2014-2015 flu season.
      • 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 and was 5.8% for the week ending May 5, 2018 (week 18). The percentage is below the epidemic threshold of 6.8% for week 18 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
    • NCHS data are 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:
    • One influenza-associated pediatric death was reported to CDC during week 20.
      • This death was associated with an influenza B virus and occurred during week 16 (the week ending April 21, 2018).
    • A total of 169 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 May 19 was 2.2%.
    • Regionally, the three-week average percent of specimens testing positive for influenza in clinical laboratories ranged from 1.0% to 7.9%.
    • During the week ending May 19, of the 186 (2.2%) influenza-positive tests reported to CDC by clinical laboratories, 85 (45.7%) were influenza A viruses and 101 (54.3%) were influenza B viruses.
    • Influenza A(H3) viruses have predominated this season. Since early March, influenza B viruses have been more frequently reported than influenza A viruses.
    • During the week ending May 19, 6 (33.3%) of the 18 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 12 (66.7%) were influenza B viruses. Of the 6 influenza A viruses that were subtyped, 2 (33.3%) were H3N2 viruses and 4 (66.6%) were (H1N1)pdm09 viruses.
    • The majority of the influenza viruses collected from the United States during October 1, 2017 through April 28, 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 1,124 influenza A(H1N1)pdm09, 2,347 influenza A(H3N2), and 1,087 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, 11 (1.0%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but were 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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