According to this week’s FluView report from the Centers for Disease Control and Prevention (CDC), seasonal influenza activity remains low overall in the United States. For the week ending December 12, the proportion of people seeing their healthcare provider for influenza-like illness (ILI) is 1.9%, and remains below the national baseline (2.1%). Four of 10 regions (Regions 2, 3, 4 and 6) reported ILI at or above their region-specific baseline levels.
One state (South Carolina) experienced high ILI activity. Puerto Rico and one state (New Jersey) experienced moderate ILI activity. New York City and two states (Minnesota and Virginia) experienced low ILI activity. 46 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. Guam reported widespread influenza activity. Puerto Rico and two states (Maryland and New Hampshire) reported regional activity. Twelve states (Alabama, Arizona, Connecticut, Idaho, Iowa, Kentucky, Massachusetts, Nevada, New Jersey, North Carolina, Texas, and Utah) reported local influenza activity. The District of Columbia, the U.S. Virgin Islands and 33 states reported sporadic influenza activity. No influenza activity was reported by three states (Delaware, Mississippi, and Rhode Island). Geographic spread data show how many areas within a state or territory are seeing flu activity.
Influenza-associated hospitalization data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) for the 2015-2016 influenza season will be updated weekly starting later this season.
The proportion of deaths attributed to pneumonia and influenza (P&I) based on the NCHS Mortality Surveillance System and the 122 Cities Mortality Reporting System is below their system-specific epidemic threshold. Two influenza-associated pediatric deaths were reported to CDC during the week ending December 5. No influenza-associated pediatric deaths were reported to CDC during the week ending December 12. A total of 3 influenza-associated pediatric deaths have been reported for the 2015-2016 season at this time.
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending December 12 was 1.7%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories ranged from 0.5% to 3.9%. During the week ending December 12, 117 (56.3%) of the influenza-positive tests reported to CDC by clinical laboratories were influenza A viruses and 91 (43.8%) were influenza B viruses.
The most frequently identified influenza virus type reported by public health laboratories during the week ending December 12 was influenza A viruses, with influenza A (H1N1)pdm09 viruses predominating. During the week ending December 12, 30 (73.2%) of the 41 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 11 (26.8%) were influenza B viruses. Of the 28 influenza A viruses that were subtyped, 11 (39.3%) were H3 viruses and 17 (60.7%) were A (H1N1)pdm09 viruses. Cumulatively from October 4-December 12, 2015, influenza A (H3) viruses were predominant in all age groups ranging from 32.8% (ages 0-4 years) to 80.9% (ages 65 years and older).
One human infection with a novel influenza A virus was reported by the state of Minnesota. The person was infected with an influenza A (H1N1) variant (H1N1v) virus. The patient was not hospitalized and has fully recovered from their illness. The patient lived and worked in an area near where swine were housed but no direct contact with swine was reported in the week prior to illness onset. No ongoing human-to-human transmission has been identified.
The CDC has characterized 134 specimens (18 influenza A (H1N1)pdm09, 100 influenza A (H3N2) and 16 influenza B viruses) collected in the U.S. since October 1, 2015. All 18 (100%) influenza A (H1N1)pdm09 viruses were antigenically characterized as similar to A/California/7/2009, the influenza A (H1N1) component of the 2015-2016 Northern Hemisphere vaccine. All 100 H3N2 viruses were genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015-2016 Northern Hemisphere vaccine. A subset of 53 H3N2 viruses also were antigenically characterized; 52 of 53 (98.1%) H3N2 viruses were similar to A/Switzerland/9715293/2013 by HI testing or neutralization testing. All nine (100%) of the B/Yamagata-lineage viruses were antigenically characterized as similar to B/Phuket/3073/2013, which is included in both the 2015–16 Northern Hemisphere trivalent and quadrivalent vaccines. All seven (100%) of the B/Victoria-lineage viruses were antigenically characterized as similar to B/Brisbane/60/2008, which is included in the 2015-16 Northern Hemisphere quadrivalent vaccine.
Since October 1, 2015, CDC has tested 25 influenza A (H1N1)pdm09, 117 influenza A (H3N2), and 21 influenza B viruses for resistance to the neuraminidase inhibitors antiviral drugs. While the vast majority of the viruses that have been tested are sensitive to oseltamivir, zanamivir, and peramivir, one influenza A (H1N1)pdm09 virus was reported during the week ending December 12 that showed resistance to oseltamivir and peramivir (but was sensitive to zanamivir).