Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to this week’s FluView report while influenza activity continues to decrease, it remains slightly elevated nationally. Sporadic flu activity may continue for a number of weeks, especially in parts of the country where activity started later. CDC continues to recommend vaccination as long as influenza viruses are circulating. It's also important that people at high risk for serious flu complications who develop flu-like symptoms or anyone with severe illness consult a health care provider to see whether influenza antiviral drugs might be needed. Below is a summary of the key indicators for the week of February 16-22, 2014:
- For the week of February 16-22, the national proportion of people seeing their health care provider for influenza-like illness decreased for the eighth week, but remains slightly above the national baseline. Eight of 10 regions continue to report ILI activity above their region-specific baseline level. Additional information regarding regional activity is available through FluView Interactive.
- Two states (Hawaii and Oklahoma) experienced high ILI activity; no states experienced high ILI activity last week. Two states (Minnesota and Texas) experienced moderate ILI activity. Ten states experienced low ILI activity. Thirty-six states and New York City 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.
- Ten states reported widespread geographic influenza activity. This is a decrease from the 17 states that reported widespread activity in the previous week. Twenty-two states reported regional activity. Guam, Washington DC and fourteen states reported local activity. Puerto Rico and four states reported sporadic influenza activity. The U.S. Virgin Islands reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
- 7,406 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2013. This translates to a cumulative overall rate of 27.4 hospitalizations per 100,000 people in the United States. Last season, the overall hospitalization rate for all age groups during the same time period was 36.7 per 100,000 people. More data for hospitalization rates are available through FluView Interactive.
- The highest hospitalization rates are among people 65 and older (58.2 per 100,000), followed by people 50-64 years (43.2 per 100,000) and children younger than 5 years (38.8 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
- Of the 7,406 influenza-associated hospitalizations that have been reported this season, more than 60% have been in people 18 to 64 years old. This pattern of more hospitalizations among younger people was also seen during the 2009 H1N1 pandemic.
- Hospitalization data are collected from 13 states and represent approximately 8.5% 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 decreased for the fourth consecutive week, but remains slightly above the epidemic threshold. When the proportion of the deaths due to P&I is above the epidemic threshold it means that the number of P&I deaths occurring are in excess of the number that is expected.
- Nine influenza-associated pediatric deaths were reported to CDC during the week of February 16-22 (week 8). Five deaths were associated with a 2009 H1N1 virus, three deaths were associated with an influenza A virus for which subtyping was not performed and one death was associated with an influenza B virus. A total of 61 influenza-associated pediatric deaths have been reported for the 2013-2014 season at this time. Additional information about the pediatric deaths from this season and previous seasons is available through FluView Interactive.
- Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week of February 16-22 decreased to 10.8%. Averaged over the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 8.2% to 27.1%.
- Influenza A (H3N2), 2009 influenza A (H1N1), and influenza B viruses have all been identified in the U.S. this season. To date, 2009 H1N1 viruses have predominated. This is the H1N1 virus that emerged in 2009 to cause a pandemic. 2009 H1N1 viruses have continued to circulate among people since that time, but this is the first season that the virus has circulated at such high levels since the pandemic. During the week of February 16-22, 612 (83%) of the 738 influenza-positive tests reported to CDC were influenza A viruses and 126 (17%) were influenza B viruses. Of the 362 influenza A viruses that were subtyped, 7% were H3 viruses and 93% were 2009 H1N1 viruses.
- CDC has antigenically characterized 1,281 influenza viruses, including 1,113 viruses identified as 2009 H1N1 viruses, 118 influenza A (H3N2) viruses, and 50 influenza B viruses, collected since October 1, 2013.
- 1,112 (99.9%) of the 1,113 2009 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 118 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.
- 31 (62%) of the 50 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 19 (38%) other influenza B viruses belonged to the B/Victoria lineage of viruses, and were characterized as B/Brisbane/60/2008-like. This is the recommended influenza B component of the 2013-2014 Northern Hemisphere quadrivalent influenza vaccine.
- Since October 1, 2013, CDC has tested 3,733 2009 H1N1, 217 influenza A (H3N2), and 90 influenza B virus samples for resistance to the neuraminidase inhibitor influenza antiviral drugs. While the vast majority of the 2009 H1N1 viruses that have been tested are sensitive to oseltamivir and zanamivir, two additional 2009 H1N1 virus showed resistance to oseltamivir during the week of February 16-22. So far this season 28 (0.8%) 2009 H1N1 viruses have shown resistance to oseltamivir. No influenza A (H3N2) or influenza B viruses have shown resistance to oseltamivir. No viruses have shown resistance to zanamivir.
- The neuraminidase inhibitors oseltamivir and zanamivir are currently the only recommended influenza antiviral drugs.
- As in recent past seasons, high levels of resistance to the adamantanes (amantadine and rimantadine) continue to persist among 2009 H1N1 and influenza A (H3N2) viruses. Adamantanes are not effective against influenza B viruses. Adamantanes are not recommended for use against influenza this season.
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.