Situation Update: Summary of Weekly FluView

Key Flu Indicators

According to the latest FluView report, seasonal influenza activity is approaching summertime levels in the United States. It’s important to remember, though, that flu viruses continue to circulate at low levels during the summer in the United States and the Southern Hemisphere is entering its regular flu season. Below is a summary of the key indicators for the week of May 5-11, 2013.

• For the week of May 5-11, 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 eighth consecutive week.
• One state (Hawaii) experienced low activity, and 49 states and New York City experienced minimal ILI activity. The District of Columbia 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.
• 49 states, Guam, and Puerto Rico reported local, sporadic, or no geographic spread of influenza activity. Only 1 state (Hawaii) reported regional geographic influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
• An additional 18 laboratory-confirmed influenza hospitalizations were reported during the week of May 5-11; bringing the total number of hospitalizations that occurred from October 1, 2012 through April 30, 2013 to 12,348. This 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 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 decreased this week and remains below the epidemic threshold.
• One influenza-related pediatric death was reported during the week of May 5-11, 2013. The death was associated with an influenza A virus for which the subtype was not determined. This brings the total number of influenza-associated pediatric deaths reported to CDC for 2012-2013 to 139. 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 5-11 increased slightly, but remains low and is approaching levels that are typically observed during the summer.
• 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 5-11, 30 of the 124 influenza-positive tests reported to CDC were influenza A viruses and 94 were influenza B viruses. Of the 7 influenza A viruses that were subtyped, 4 were H3 viruses and 3 were 2009 H1N1 viruses.
• Since October 1, 2012, CDC has antigenically characterized 2,391 influenza viruses, including 234 2009 influenza A (H1N1) viruses, 1,324 influenza A (H3N2) viruses and 833 influenza B viruses.
  • Of the 234 2009 influenza A (H1N1) characterized, 231 (98.7%) 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 833 influenza B viruses characterized, 66.5% 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 33.5% of the tested influenza B viruses belonged to the B/Victoria lineage of viruses.
• Since October 1, 2012, 540 2009 influenza A (H1N1), 2,119 influenza A (H3N2), and 935 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 and one A(H3N2) virus was 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.