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Situation Update: Summary of Weekly FluView

The May 11-17, 2014 FluView marks the final full influenza surveillance report for the 2013-2014 flu season in the United States. Influenza surveillance in the U.S. will continue through the summer months with condensed reports available at http://www.cdc.gov/flu/weekly/, though the summary key points available on this page will no longer be updated.

Key Flu Indicators

According to the latest FluView report, seasonal flu activity is low and declining, though flu viruses continue to circulate and cause illness in the United States. Below is a summary of the key indicators for the week ending May 17, 2014 (week 20):

  • For the week ending May 17, the national proportion of people seeing their health care provider for influenza-like illness (ILI) decreased and has now been below the national baseline of 2.0% for ten weeks. ILI was above or at baseline for 15 weeks this season. One of 10 regions (Region 1) reported ILI above region-specific baseline levels. Additional information regarding regional activity and previous seasons is available through FluView Interactive.
  • Forty-nine states and New York City experienced minimal ILI activity. One state (Texas) experienced low 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.
  • Two states (Maryland and New York) reported widespread geographic influenza activity. This is a slight decrease from the three states that reported widespread activity in the previous week. Guam and five states reported regional activity. Six states reported local activity. Puerto Rico, the District of Columbia, and 32 states reported sporadic influenza activity. Five states (Arkansas, Kansas, Mississippi, North Carolina, and Tennessee) reported no influenza activity. The U.S. Virgin Islands did not report. Geographic spread data show how many areas within a state or territory are seeing flu activity.
  • 9,632 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2013. This translates to a cumulative overall rate of 35.6 hospitalizations per 100,000 people in the United States. More data on hospitalization rates are available through FluView Interactive.
    • The highest hospitalization rates are among people 65 and older (88.1 per 100,000), followed by people 50-64 years (54.3 per 100,000) and children younger than 5 years (46.7 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
    • Of the 9,632 influenza-associated hospitalizations that have been reported this season, approximately 60% have been in people 18 to 64 years old. This trend of increased hospitalizations among younger people was also seen during the 2009 H1N1 pandemic.
    • Hospitalization data are collected from 13 states and represent approximately 8.5% 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 decreased to 5.8% and remains below the epidemic threshold (6.8%).
  • One influenza-associated pediatric death was reported to CDC during the week of May 11-17, 2014 (week 20). This death was associated with an influenza B virus and occurred during week 19 (week ending May 10, 2014). A total of 95 influenza-associated pediatric deaths have been reported for the 2013-2014 season at this time. Additional information about reported pediatric deaths during this season and previous seasons is available through FluView Interactive.
  • Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week ending May 17, 2014 decreased to 8.7%. Averaged over the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 4.0% to 16.8%.
  • Influenza A (H3N2), 2009 H1N1, and influenza B viruses have all been identified in the U.S. this season. 2009 H1N1 viruses have predominated overall during the 2013-14 season, though influenza B viruses have accounted for the largest proportion of circulating viruses during the past two months and the proportion of influenza A (H3) viruses has been increasing as well. During the week ending May 17, 139 (41.0%) of the 339 influenza-positive tests reported to CDC were influenza A viruses and 200 (59.0%) were influenza B viruses. Of the 50 influenza A viruses that were subtyped, all were H3 viruses.
  • CDC has antigenically characterized 2,815 influenza viruses; 2,008 2009 H1N1 viruses, 426 influenza A (H3N2) viruses, and 381 influenza B viruses, collected since October 1, 2013.
    • 2,005 (99.8%) of the 2,008 2009 H1N1 viruses tested were characterized as A/California/7/2009-like. This is the influenza A (H1N1) component of the Northern Hemisphere quadrivalent and trivalent vaccines for the 2013-2014 season.
    • 406 (95.3%) of the 426 influenza A (H3N2) viruses tested were characterized as Texas/50/2012-like. This is the influenza A (H3N2) component of the Northern Hemisphere quadrivalent and trivalent vaccines for the 2013-2014 season.
    • 269 (70.6%) of the 381 influenza B viruses tested belonged to the B/Yamagata lineage of viruses. 268 (99.6%) of these 269 viruses were characterized as B/Massachusetts/02/2012-like. This is an influenza B component for the 2013-2014 Northern Hemisphere quadrivalent and trivalent influenza vaccines.
    • The 112 (29.4%) 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 2013-2014 Northern Hemisphere quadrivalent influenza vaccine.
  • Since October 1, 2013, CDC has tested 5,100 2009 H1N1, 667 influenza A (H3N2), and 505 influenza B virus samples for resistance to the neuraminidase inhibitor influenza antiviral drugs. So far this season, 59 (1.2%) 2009 H1N1 viruses have shown resistance to oseltamivir. No influenza A (H3N2) or influenza B viruses have shown resistance to oseltamivir. No viruses have shown resistance to 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 H1N1 and influenza A (H3N2) viruses. Adamantanes are not effective against influenza B viruses. Adamantanes are not recommended for use against influenza this season.

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 2013-2014 season can be found on the current FluView.

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