U.S. Situation Update
Key Flu Indicators
According to this week’s FluView report, flu activity continued to increase in the United States. High levels of activity are being reported in the South and Midwest states. Flu activity is expected to increase further in the coming weeks. If you have not been vaccinated yet this season, get vaccinated now. Below is a summary of the key flu indicators for the week ending December 13, 2014:
- For the week ending December 13, the proportion of people seeing their health care provider for influenza-like illness (ILI) increased to 3.7% and is above the national baseline for the fourth consecutive week. Nine of 10 U.S. regions reported ILI activity at or above region-specific baseline levels.
- Puerto Rico and 13 states (Alabama, Arkansas, Georgia, Illinois, Indiana, Kansas, Louisiana, Minnesota, Mississippi, Missouri, Oklahoma, Texas, and Virginia) experienced high ILI activity, an increase from six states in the previous week. Six states (Idaho, Kentucky, Maryland, North Carolina, Utah, and Wisconsin) experienced moderate ILI activity. New York City and five states experienced low ILI activity. Twenty-six 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.
- Widespread influenza activity was reported by Guam and 29 states. This is an increase from 14 states that reported widespread activity last week. Puerto Rico and 14 states reported regional geographic influenzaactivity. The U.S. Virgin Islands, The District of Columbia and five states (Alaska, Arizona, Idaho, New Jersey, and New Mexico) reported local activity. Two states (Hawaii and Wyoming) reported sporadic influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.
- 1,702 laboratory-confirmed influenza-associated hospitalizations have been reported thru the Influenza Hospitalization Surveillance Network (FluSurv-NET) since October 1, 2014. This translates to a cumulative overall rate of 6.2 hospitalizations per 100,000 people in the United States.
- The highest hospitalization rates are among people 65 years and older (23.6 per 100,000 populations).
- 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.
- Four influenza-associated pediatric deaths were reported to CDC during the week ending December 13. Two deaths were associated with an influenza A (H3) virus and occurred during week 49 (week ending December 6, 2014). One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 50 (week ending December 13, 2014), and one death was associated with an influenza B virus and occurred during week 49. A total of 11 influenza-associated pediatric deaths have been reported for the 2014-2015 season at this time.
- Nationally, the percentage of respiratory specimens testing positive for influenza viruses in the United States during the week ending December 13 increased once again to 25.9%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses ranged from 8.2% to 32.5%.
- Influenza A (H3N2) viruses have been identified most commonly in the United States this season. Fewer influenza B viruses have been detected and very few influenza A (H1N1)pdm09 viruses have been detected. During the week ending December 13, 5,006 (96.3%) of the 5,200 influenza-positive tests reported to CDC were influenza A viruses and 194 (3.7%) were influenza B viruses. Of the 1,901 influenza A viruses that were subtyped, 99.6 % were influenza A (H3) viruses and 0.4% were influenza A (H1N1)pdm09 viruses.
- CDC has antigenically or genetically characterized 248 influenza viruses, including ten influenza A(H1N1)pdm09, 209 influenza A (H3N2) viruses and 29 influenza B viruses, collected in the United States since October 1, 2014.
- All 10 influenza A (H1N1)pdm09 viruses tested were characterized as A/California/7/2009-like. This is the influenza A (H1N1) component of the 2014-2015 Northern Hemisphere quadrivalent and trivalent influenza vaccine.
- Sixty-four (30.6%) of the 209 influenza A (H3N2) viruses tested have been characterized as A/Texas/50/2012-like. This is the influenza A (H3N2) component of the 2014-2015 Northern Hemisphere quadrivalent and trivalent influenza vaccine.
- The remaining 145 (69.4%) influenza A (H3N2) viruses tested showed either reduced titers with antiserum produced against A/Texas/50/2012 or belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012. The majority of these 145 influenza A (H3N2) viruses were antigenically similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015 Southern Hemisphere influenza vaccine.
- Twenty (69%) of the 29 influenza B viruses tested belonged to the B/Yamagata/16/88 lineage and were characterized as B/Massachusetts/2/2012-like. This is an influenza B component of the 2014-2015 Northern Hemisphere trivalent and quadrivalent influenza vaccine.
- Seven (78%) of the nine 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 2014-2015 Northern Hemisphere quadrivalent influenza vaccine. Two (22%) of the B/Victoria-lineage viruses tested showed reduced titers to B/Brisbane/60/2008.
- Since October 1, 2014, CDC has tested 10 influenza A (H1N1)pdm09, 175 influenza A (H3N2), and 51 influenza B viruses for resistance to neuraminidase inhibitors (oseltamivir and zanamivir). All viruses showed susceptibility to both oseltamivir and 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 influenza A (H1N1)pdm09 and A (H3N2) viruses. Adamantanes are not effective against influenza B viruses.