Situation Update: Summary of Weekly FluView

Key Flu Indicators

According to the final full FluView report for the 2012-2013 season, seasonal influenza activity remains low in the United States. Below is a summary of the key indicators for the week of May 12-18, 2013.

• For the week of May 12-18, the proportion of people seeing a health care provider for influenza-like illness (ILI) continued to decrease and remains below the national baseline for the ninth consecutive week.
• 49 states and New York City experienced minimal ILI activity. The District of Columbia and 1 state (Alaska) had insufficient data to determine an ILI activity level. ILI activity data indicate the amount of flu-like illness that is occurring in each jurisdiction.
• All 50 states, Guam, and Puerto Rico reported local, sporadic, or no geographic spread of influenza activity. No states reported regional or widespread geographic influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
• A total of 12,343 hospitalizations that occurred from October 1, 2012 through April 30, 2013 were reported, which translates to a cumulative rate of 44.3 influenza-associated hospitalizations per 100,000 people in the United States.
  • Data regarding hospitalizations for the 2012-3013 season will continue to be updated and adjusted as additional charts are reviewed and data is received by CDC; though no new information regarding persons admitted for hospitalization after April 30, 2013 will be collected.
• The proportion of death attributed to pneumonia and influenza (P&I) based on the 122 Cities Mortality Reporting System increased slightly this week but remains below the epidemic threshold and near levels that are typically observed during the summer.
• Seven influenza-related pediatric deaths were reported during the week of May 12-18, 2013.  One death was associated with an influenza A (H3) virus, one death was associated with an influenza A for which the subtype was not determined, and one death was associated with an influenza virus for which the type was not determined.  Four deaths were associated with influenza B viruses.  This brings the total number of influenza-associated pediatric deaths reported to CDC for 2012-2013 to 146. Additional information regarding pediatric deaths is available through FluView Interactive.
• Nationally, the percentage of respiratory specimens testing positive for influenza in the United States during the week of May 12-18 decreased.
• Influenza A (H3N2), 2009 influenza A (H1N1), and influenza B viruses have all been identified in the U.S. this season. During the week of May 12-18, 18 of the 68 influenza-positive tests reported to CDC were influenza A viruses and 50 were influenza B viruses. Of the 8 influenza A viruses that were subtyped, 5 were H3 viruses and 3 were 2009 H1N1 viruses.
• Since October 1, 2012, CDC has antigenically characterized 2,452 influenza viruses, including 252 2009 influenza A (H1N1) viruses, 1,324 influenza A (H3N2) viruses and 876 influenza B viruses.
  • Of the 252 2009 influenza A (H1N1) characterized, 249 (98.8%) were characterized as A/California/7/2009-like. This is the influenza A (H1N1) component of the Northern Hemisphere vaccine for the 2012-2013 season.
  • Of the 1,324 influenza A (H3N2) viruses, 1,319 (99.6%) were characterized as A/Victoria/361/2011-like. This is the influenza A (H3N2) component of the Northern Hemisphere influenza vaccine for the 2012-2013 season.
  • Of the 876 influenza B viruses characterized, 66.3% belonged to the B/Yamagata lineage of viruses, and were characterized as B/Wisconsin/1/2010-like, the influenza B component for the 2012-2013 Northern Hemisphere influenza vaccine. The remaining 33.7% of the tested influenza B viruses belonged to the B/Victoria lineage of viruses.
• Since October 1, 2012, 542 2009 influenza A (H1N1), 2,123 influenza A (H3N2), and 961 influenza B virus samples have been tested for resistance to neuraminidase inhibitors. While the vast majority of the tested virus samples (>99%) showed susceptibility to the antiviral drugs oseltamivir and zanamivir, two 2009 H1N1 viruses (reported during week 3 and week 6) and two influenza A (H3N2) viruses (reported during weeks 10 and 11) showed resistance to oseltamivir. One of the A(H3N2) viruses were resistant to both oseltamivir and zanamivir. High levels of resistance to the adamantanes (amantadine and rimantadine) 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 2012-2013 season can be found on the current FluView.