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Situation Update: Summary of Weekly FluView

Key Flu Indicators

According to this week’s FluView report, flu activity increased in the United States. Widespread and high ILI activity is being reported in parts of the U.S. Flu activity is expected to increase further in the coming weeks. 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 December 6, 2014:

  • For the week ending December 6, the proportion of people seeing their health care provider for influenza-like illness (ILI) is above the national baseline. Eight of 10 U.S. regions reported ILI activity at or above region-specific baseline levels.
  • Puerto Rico and six states (Alabama, Georgia, Illinois, Louisiana, Mississippi, and Texas) experienced high ILI activity. Two states (Florida and Indiana) experienced moderate ILI activity. Seven states (Idaho, Kansas, Maryland, Missouri, South Carolina, Utah, and Virginia) experienced low ILI activity. New York City and 35 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.
  • Widespread influenza activity was reported by fourteen states (Colorado, Delaware, Florida, Georgia, Illinois, Kentucky, Louisiana, Maryland, Minnesota, New York, North Carolina, Ohio, Pennsylvania, and Texas). This is an increase from six states that reported widespread activity last week. Guam, Puerto Rico, and 25 states reported regional geographic influenzaactivity; an increase from the fourteen states that reported regional activity last week. The U.S. Virgin Islands and seven states (Arizona, Idaho, Nebraska, New Hampshire, New Jersey, New Mexico, and Oregon) reported local activity. The District of Columbia and four states (California, Hawaii, South Dakota, and Wyoming) reported sporadic influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
  • 1,028 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2014. This translates to a cumulative overall rate of 3.8 hospitalizations per 100,000 people in the United States.
    • The highest hospitalization rates are among people 65 years and older (13.4 per 100,000 populations).
    • 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.
  • The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Mortality Reporting System increased again this week, but remains below the epidemic threshold.
  • Two influenza-associated pediatric deaths were reported to CDC during the week ending December 6. A total of 7 influenza-associated pediatric deaths have been reported for the 2014-2015 season at this time.
  • Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week ending December 6 increased once again to 21.2%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 4.5% to 27.5%.
  • Influenza A (H3N2) viruses have been identified most commonly in the United States this season. Fewer influenza B viruses have been detected and very few influenza A (H1N1) pdm09 viruses have been detected. During the week ending December 6, 3,252 (95.2%) of the 3,415 influenza-positive tests reported to CDC were influenza A viruses and 163 (4.8%) were influenza B viruses. Of the 1,261 influenza A viruses that were subtyped, 99.4 % were influenza A (H3) viruses and 0.5% were influenza A (H1N1) pdm09 viruses.
  • CDC has antigenically or genetically characterized 236 influenza viruses, including ten A(H1N1) pdm09, 197 A(H3N2) viruses and 29 influenza B viruses, collected in the United States since October 1, 2014.
    • All 10 influenza A (H1N1)pdm09 viruses tested were 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.
    • Sixty-four (32.5%) of the 197 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 133 (67.5%) influenza A (H3N2) viruses tested showed either reduced titers with antiserum produced against A/Texas/50/2012 or belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012. The majority of these 133 influenza A (H3N2) viruses were antigenically similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015 Southern Hemisphere influenza vaccine.
    • Twenty (69%) of the 29 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.
    • Seven (78%) of the nine 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. Two (22%) of the B/Victoria-lineage viruses tested showed reduced titers to B/Brisbane/60/2008.
  • Since October 1, 2014, CDC has tested five A (H1N1) pdm09, 106 A (H3N2), and 28 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 influenza A (H1N1)pdm09 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.