Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to this week’s FluView report, flu activity remains low overall across the United States, but is increasing in parts of the nation, most notably 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 17-23, 2013:
- For the week of November 17-23, 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 at or above their region-specific baseline level. The other eight regions reported activity levels below region-specific baselines.
- Two states (Mississippi and Texas) experienced high ILI activity. One state (Alabama) experienced moderate ILI activity. One state (Louisiana) experienced low ILI activity. Forty-five states and New York City experienced minimal ILI activity. The District of Columbia and Montana 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.
- Six states (Alabama, Florida, Kentucky, Mississippi, Texas, and Utah) reported regional geographic influenza activity; an increase from four jurisdictions in the previous week. Ten states (Alaska, Arkansas, Colorado, Georgia, Louisiana, Massachusetts, Minnesota, Oklahoma, South Carolina, and Virginia) reported local activity. The District of Columbia, Guam, Puerto Rico, and 32 states reported sporadic influenza activity. The U.S. Virgin Islands and two states (Maine and 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 will be reported starting with the FluView published on December 6, 2013.
- The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Mortality Reporting System remained below the epidemic threshold.
- No influenza-related pediatric deaths were reported to CDC during the week of November 17-23. A total of two 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 17-23 increased for the fourth week from 7.6% to 7.9%. During the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 1.5% in the Northeast to 13.2% in the Southeast.
- 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 17-23, 348 of the 397 influenza-positive tests reported to CDC were influenza A viruses and 49 were influenza B viruses. Of the 222 influenza A viruses that were subtyped 5.4% were H3 viruses and 94.6% were 2009 H1N1 viruses.
- CDC has antigenically characterized 83 influenza viruses, including 62 2009 influenza A (H1N1) viruses, 20 influenza A (H3N2) viruses, and one influenza B virus, collected since October 1, 2013.
- All 62 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 20 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.
- The one influenza B virus tested belonged to the B/Yamagata lineage of viruses, and was characterized as B/Massachusetts/02/2012-like. This is an influenza B component for the 2013-2014 Northern Hemisphere quadrivalent and trivalent influenza vaccines.
- Since October 1, 2013, CDC has tested 217 2009 influenza A (H1N1), 42 influenza A (H3N2), and nine 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, two additional 2009 H1N1 virus proved resistant to oseltamivir during the week of November 17-23, though both were sensitive to zanamivir. In total, six 2009 H1N1 viruses have shown resistance to oseltamivir so far this season, though each of the viruses has been sensitive to 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.
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.