Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to this week's FluView report, flu activity continues to increase in parts of the United States, particularly in the South Central and Southeast regions of the country. Additional increases in activity are likely in the coming weeks. People who have not already gotten a flu vaccine for the 2013-2014 season should do so now. Below is a summary of the key indicators for the week of November 24-30, 2013:
- For the week of November 24-30, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased, but remains below the national baseline. The Southeast and South Central regions (Regions 4 and 6) reported ILI activity above their region-specific baseline level. The other eight regions reported activity levels below region-specific baselines.
- Mississippi and Texas experienced high ILI activity again this week. Two states (Alabama and Louisiana) experienced moderate ILI activity. New York City and two states (Arkansas and Delaware) experienced low ILI activity. Forty-four 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.
- Nine states reported regional geographic influenza activity; an increase from six jurisdictions in the previous week. Thirteen states reported local activity. This is an increase from ten states last week. The District of Columbia, Guam, Puerto Rico, and 27 states reported sporadic influenza activity. The U.S. Virgin Islands and one states (Vermont) reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
- Data regarding influenza-associated hospitalizations for the 2013-2014 influenza season is now available. Since October 1, 2013, 333 laboratory-confirmed influenza-associated hospitalizations have been reported. This translates to a cumulative rate of 1.2 hospitalizations per 100,000 people in the United States.
- Hospitalization data are collected from 15 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 remains below the epidemic threshold.
- One influenza-associated pediatric death was reported to CDC during the week of November 24-30. The death was associated with a 2009 H1N1 virus. A total of three influenza-associated pediatric deaths have been reported for the 2013-2014 season.
- Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week of November 24-30 increased for the fifth consecutive week from 9.0% to 10.1%. During the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 2.2% to 13.8%.
- 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 November 24-30, 501 of the 536 influenza-positive tests reported to CDC were influenza A viruses and 35 were influenza B viruses. Of the 221 influenza A viruses that were subtyped 3.6% were H3 viruses and 96.4% were 2009 H1N1 viruses.
- CDC has antigenically characterized 156 influenza viruses, including 120 2009 influenza A (H1N1) viruses, 31 influenza A (H3N2) viruses, and 5 influenza B virus, collected since October 1, 2013.
- All 120 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 31 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 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 three 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 265 2009 influenza A (H1N1), 46 influenza A (H3N2), and 11 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, six 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.