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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 15, 2014:

  • For the week ending November 15, 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 high 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.
  • Puerto Rico and five states (Alaska, Florida, Louisiana, Massachusetts and Texas) reported regional geographic influenza activity. 21 states reported local activity. The U.S. Virgin Islands, the District of Columbia, and 23 states reported sporadic influenza activity. One state (Rhode Island) reported no influenza activity. Guam did not report. 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 15 increased once again to 9.3%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 0.9% to 18.2%.
  • 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 15, 836 (87.5%) of the 955 influenza-positive tests reported to CDC were influenza A viruses and 119 (12.5%) were influenza B viruses. Of the 257 influenza A viruses that were subtyped, all were influenza A (H3) viruses.
  • CDC has antigenically characterized 52 influenza viruses, including one 2009 H1N1 virus, 34 influenza A (H3N2) viruses, and 17 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.
    • 19 (56%) of the 34 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 remaining 15 (44%) influenza A (H3N2) viruses tested showed reduced titers with antiserum produced against A/Texas/50/2012. The majority of these 15 influenza A (H3N2) viruses were antigenically similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015 Southern Hemisphere influenza vaccine.
    • Ten (58.8%) of the 17 influenza B viruses tested belonged to the B/Yamagata/16/88 lineage and were characterized as B/Massachusetts/2/2012-like. This is an influenza B component of the 2014-2015 Northern Hemisphere trivalent and quadrivalent influenza vaccine.
    • The seven (41.2%) other influenza B viruses belonged to the B/Victoria lineage of viruses, and were characterized as B/Brisbane/60/2008-like. This is the recommended influenza B component of the 2014-2015 Northern Hemisphere quadrivalent influenza vaccine.
  • Since October 1, 2014, CDC has tested two 2009 H1N1, 15 influenza A (H3N2), and seven 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.

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