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Situation Update: Summary of Weekly FluView

Key Flu Indicators

According to this week’s FluView report, overall seasonal flu activity remains low across the United States. Increases in flu activity are expected in the coming weeks. Below is a summary of the key flu indicators for the week ending November 8, 2014:

  • For the week ending November 8, the proportion of people seeing their health care provider for influenza-like illness (ILI) was below the national baseline. All 10 U.S. regions reported ILI activity below region-specific baseline levels.
  • Puerto Rico experienced moderate ILI activity. Two states (Alaska and Louisiana) experienced low ILI activity. New York City and 48 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 geographic influenza activity. Three states (Alaska, Florida, and Massachusetts) reported regional influenza activity. Puerto Rico, the U.S. Virgin Islands and 13 states reported local activity. The District of Columbia and 31 states reported sporadic influenza activity. Three states (Maine, Rhode Island and Tennessee) reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
  • Data regarding influenza-associated hospitalizations for the 2014-2015 influenza season will be available starting later this season.
  • The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Mortality Reporting System is below the epidemic threshold.
  • No influenza-associated pediatric deaths were reported to CDC during the week ending November 8. One influenza-associated pediatric death has been reported for the 2014-2015 season and occurred during the week ending October 4, 2014.
  • Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week ending November 8 increased once again to 7.4%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 0.7% to 14.5%.
  • Influenza A (H3N2) and influenza B viruses have been identified most commonly in the United States this season. Very few 2009 H1N1 viruses have been reported. During the week ending November 8, 567 (83.6%) of the 678 influenza-positive tests reported to CDC were influenza A viruses and 111 (16.4%) were influenza B viruses. Of the 194 influenza A viruses that were subtyped, 99% were H3 viruses and 1.0% were 2009 H1N1 viruses.
  • CDC has antigenically characterized 19 influenza viruses, including one 2009 H1N1 virus, 13 influenza A (H3N2) viruses, and five influenza B viruses, collected in the United States since October 1, 2014.
    • The one 2009 H1N1 virus tested was characterized as A/California/7/2009-like. This is the influenza A (H1N1) component of the 2014-2015 Northern Hemisphere quadrivalent and trivalent influenza vaccine.
    • Seven (54%) of the 13 influenza A (H3N2) viruses tested have been characterized as A/Texas/50/2012-like. This is the influenza A (H3N2) component of the 2014-2015 Northern Hemisphere quadrivalent and trivalent influenza vaccine.
    • The majority of the remaining six (46%) H3N2 viruses were antigenically similar to A/Switzerland/9715293/2013. This is the H3N2 virus selected for the 2015 Southern Hemisphere influenza vaccine.
    • All five B/Victoria-lineage viruses were characterized as B/Brisbane/60/2008-like. This is an influenza B component of the 2014-2015 Northern Hemisphere quadrivalent influenza vaccine. Both B/Victoria and B/Yamagata-lineage viruses are currently circulating in the United States. However, to date, results of antigenic characterization are available only for B/Victoria lineage viruses.
  • Since October 1, 2014, CDC has tested one 2009 H1N1, 11 influenza A (H3N2), and five influenza B viruses for resistance to neuraminidase inhibitors (oseltamivir and zanamivir). All viruses showed susceptibility to both oseltamivir and zanamivir.
    • The neuraminidase inhibitors oseltamivir and zanamivir are currently the only recommended influenza antiviral drugs.
    • As in recent past seasons, high levels of resistance to the adamantanes (amantadine and rimantadine) continue to persist among 2009 influenza A (H1N1) and A (H3N2) viruses. Adamantanes are not effective against influenza B viruses.

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 2014-2015 season can be found on the current FluView.