Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to this week's FluView report, flu activity is increasing overall nationally, and is already high in Texas, Louisiana, Mississippi, and Alabama. Nationwide increases are expected in the coming weeks. Anyone 6 months and older who has not gotten a flu vaccine yet this season should get one now. Below is a summary of the key indicators for the week of December 8-14, 2013:
- For the week of December 8-14, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased, and is above the national baseline for the third week in a row. Five regions reported ILI activity at or above their region-specific baseline level. The other five regions reported activity levels below region-specific baselines.
- Alabama, Louisiana, Mississippi, and Texas experienced high ILI activity. Activity has been elevated in these states for some time now. One state (Oklahoma) experienced moderate ILI activity. New York City and six states (Colorado, Illinois, Missouri, Nevada, Utah, and Virginia) experienced low ILI activity. Thirty-seven states experienced minimal ILI activity. The District of Columbia, Idaho, and Vermont 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.
- Four states (Alabama, Louisiana, New York, and Texas) reported widespread geographic influenza activity. These are the first reports of widespread activity this season. Twenty states reported regional activity; an increase from the fourteen states that reported regional activity last week. Seventeen states reported local activity. The District of Columbia, Guam, Puerto Rico, and eight states reported sporadic influenza activity. Vermont 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.
- Since October 1, 2013, 815 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative rate of 3.0 hospitalizations per 100,000 people in the United States.
- 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 of December 8-14. One death was associated with a 2009 H1N1 virus and occurred during the week of December 8-14, 2013. A total of four influenza-associated pediatric deaths have been reported for the 2013-2014 season.
- The other death occurred during the 2012-2013 season and was associated with an influenza A virus for which the subtype was not determined. This brings the total number of pediatric deaths reported for the 2012-2013 season to 170.
- Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week of December 8-14 increased for the eighth consecutive week to 17.8%. During the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 5.4% to 20.8%.
- 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 December 8-14, 1,261 of the 1,301 influenza-positive tests reported to CDC were influenza A viruses and 40 were influenza B viruses. Of the 575 influenza A viruses that were subtyped 2.8% were H3 viruses and 97.2% were 2009 H1N1 viruses.
- CDC has antigenically characterized 317 influenza viruses, including 265 2009 influenza A (H1N1) viruses, 46 influenza A (H3N2) viruses, and 6 influenza B virus, collected since October 1, 2013.
- All 265 of the 2009 influenza A (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.
- All 46 of the 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.
- Two of the six influenza B viruses tested belonged to the B/Yamagata lineage of viruses, and 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 four other influenza B viruses belonged to the B/Brisbane lineage of viruses, were characterized as B/Brisbane/60/2008-like. This is an influenza B component of the 2013-2014 Northern Hemisphere quadrivalent influenza vaccine.
- Since October 1, 2013, CDC has tested 526 2009 influenza A (H1N1), 54 influenza A (H3N2), and 9 influenza B virus samples for resistance to neuraminidase inhibitors. While the majority of the tested viruses showed susceptibility to the antiviral drugs oseltamivir and zanamivir, seven 2009 H1N1 viruses have shown resistance to oseltamivir so far this season.
- 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.
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.