Situation Update: Summary of Weekly FluView
Key Flu Indicators
According to the latest FluView report, influenza activity continues to decrease nationwide, but remains elevated in certain indicators, most notably in the surveillance system that is used to track flu-related deaths. Below is a summary of the key indicators for the week ending March 1, 2014:
- For the week ending March 1, the national proportion of people seeing their health care provider for influenza-like illness decreased for the ninth week, reaching the national baseline of 2.0%. Five of 10 regions continue to report ILI activity at or above their region-specific baseline level. Additional information regarding regional activity is available through FluView Interactive.
- One state (Hawaii) experienced high ILI activity; two states experienced high ILI activity last week. One state (Texas) experienced moderate ILI activity. Six states experienced low ILI activity. Forty-two 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.
- Eight states reported widespread geographic influenza activity. This is a decrease from the 10 states that reported widespread activity in the previous week. Twelve states reported regional activity. Guam, Washington, D.C. and twenty-six 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.
- 7,725 laboratory-confirmed influenza-associated hospitalizations have been reported since October 1, 2013. This translates to a cumulative overall rate of 28.5 hospitalizations per 100,000 people in the United States. More data for hospitalization rates are available through FluView Interactive.
- The highest hospitalization rates are among people 65 and older (61.4 per 100,000), followed by people 50-64 years (45.1 per 100,000) and children younger than 5 years (40.3 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.
- Of the 7,725 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 increased slightly after four consecutive weeks of decreases, and remains 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.
- Four influenza-associated pediatric deaths were reported to CDC during the week ending March 1, 2014. Two deaths were associated with an influenza A virus for which subtyping was not performed, one death was associated with an influenza B virus, and one death was associated with an influenza A and B virus co-infection. A total of 65 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 ending March 1, 2014 decreased to 8.7%. Averaged over the last three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 5.8% to 22.4%.
- 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 ending March 1, 470(80%) of the 587 influenza-positive tests reported to CDC were influenza A viruses and 117 (20%) were influenza B viruses. Of the 253 influenza A viruses that were subtyped, 19.4% were H3 viruses and 80.6% were 2009 H1N1 viruses.
- CDC has antigenically characterized 1,541 influenza viruses; 1,321 2009 H1N1 viruses, 170 influenza A (H3N2) viruses, and 50 influenza B viruses, collected since October 1, 2013.
- 1,320 (99.9%) of the 1,321 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 170 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 4,002 2009 H1N1, 270 influenza A (H3N2), and 114 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, six additional 2009 H1N1 virus showed resistance to oseltamivir and were reported during the week ending March 1. So far this season 34 (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.