Situation Update: Summary of Weekly FluView Report
U.S. Situation Update
Key Flu Indicators
According to this week’s FluView report, overall seasonal influenza activity increased slightly in the United States but remains low overall. CDC recommends an annual flu vaccine for everyone 6 months of age and older. If you have not been vaccinated yet this season, get vaccinated now. Below is a summary of the key flu indicators for the week ending November 21, 2015:
- For the week ending November 21, the proportion of people seeing their health care provider for influenza-like illness (ILI) is 1.6% and remains below the national baseline (2.1%). Two of 10 regions (Regions 3 and 6) reported ILI at or above their region-specific baseline levels.
- One state (South Carolina) experienced moderate ILI activity. New York City, Puerto Rico, and 49 states 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.
- Guam reported widespread influenza activity. Puerto Rico reported regional activity. Five states (Hawaii, Iowa, Kentucky, New Hampshire, and Utah) reported local influenza activity. 39 states reported sporadic influenza activity. The District of Columbia, the U.S. Virgin Islands, and 6 states (Alabama, Delaware, Kansas, Maryland, Mississippi, and Rhode Island) reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
- Influenza-associated hospitalization data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) for the 2015-2016 influenza season will be updated weekly starting later this season.
- The proportion of deaths attributed to pneumonia and influenza (P&I) based on the NCHS Mortality Surveillance System and the 122 Cities Mortality Reporting System is below their system-specific epidemic threshold.
- The second influenza-associated pediatric death of the 2015-16 flu season was reported to CDC during week 46. This death was associated with an influenza B virus and occurred during week 44 (the week ending November 7, 2015). .
- Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending November 21 was 1.1%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories ranged from 0.2% to 2.9%.
- During the week ending November 21, 58 (48.3%) of the influenza-positive tests reported to CDC by clinical laboratories were influenza A viruses and 62 (51.7%) were influenza B viruses.
- The most frequently identified influenza virus type reported by public health laboratories during the week ending November 21 was influenza A viruses, with influenza A (H3) viruses predominating.
- During the week ending November 21, 18 (75.0%) of the 24 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 6 (25.0%) were influenza B viruses. Of the 15 influenza A viruses that were subtyped, 10 (66.7%) were H3 viruses and 5 (33.3%) were A (H1N1)pdm09 viruses.
- Influenza A (H3) viruses were predominant in all age groups ranging from 48.1% (ages 0-4 years) to 82.1% (ages 65 years and older).
- CDC has characterized 345 U.S. flu viruses collected by U.S. laboratories during May 24–September 30, 2015, including 14 influenza A (H1N1)pdm09 viruses, 260 influenza A (H3N2) viruses, and 71 influenza B viruses.
- All 14 influenza A (H1N1)pdm09 viruses were antigenically characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2015-2016 Northern Hemisphere flu vaccine..
- All 260 H3N2 viruses were genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to cell propagated A/Switzerland/9715293/2013, the influenza A (H3N2) reference virus representing the 2015-2016 Northern Hemisphere vaccine component.
- A subset of 118 H3N2 viruses also were antigenically characterized; 117 of 118 (99%) H3N2 viruses were A/Switzerland/9715293/2013-like by HI testing or neutralization testing.
- 44 (62%) of the 71 influenza B viruses collected and analyzed during this period belonged to the B/Yamagata lineage, and all were antigenically similar to the B/Phuket/3073/2013 virus, the influenza B component for both the 2015–16 Northern Hemisphere trivalent and quadrivalent vaccines.
- The remaining 27 (38%) influenza B viruses were antigenically characterized as B/Brisbane/60/2008-like, the recommended influenza B component of the 2015-16 Northern Hemisphere quadrivalent flu vaccine.
- In addition, CDC has antigenically characterized 20 specimens (1 influenza A (H1N1)pdm09, 18 influenza A (H3N2) and 1 influenza B/Yamagata-lineage) collected in the U.S. since October 1, 2015.
- The 18 H3N2 viruses collected since October 1, 2015 have been genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component for the 2015-2016 Northern Hemisphere vaccine. Ten viruses (one A (H1N1)pdm09, eight A (H3N2), and one B/Yamagata-lineage) collected since October 1, 2015 have been antigenically characterized. All ten were similar to the 2015-2016 Northern Hemisphere influenza vaccine components.
- Since October 1, 2015, CDC has tested five A (H1N1) pdm09, 14 influenza A (H3N2), and nine influenza B viruses for resistance to the neuraminidase inhibitors antiviral drugs. None of the tested viruses were found to be resistant to either oseltamivir, zanamivir, or peramivir.
Note: Delays in reporting may mean that data changes over time. The most up to date data for all weeks during the 2015-2016 season can be found on the current FluView.
- Page last reviewed: November 30, 2015
- Page last updated: November 30, 2015
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