Influenza activity increased again according to the latest FluView report. All U.S. states but Hawaii and Oregon continue to report widespread flu activity and the number of states experiencing high influenza-like illness (ILI) activity increased from 39 states plus New York City and Puerto Rico to 42 states plus New York City and the District of Columbia.
At 7.1 percent, influenza-like-illness (ILI) activity is approaching the 7.7 peak of the 2009 pandemic. The overall hospitalization rate is higher than the overall hospitalization rate reported during the same week of the 2014-2015 season; the most severe season in recent years. CDC also is reporting an additional 17 flu-related pediatric deaths, including one of which occurred during the 2015-2016 season, bringing the total number of flu-related pediatric deaths reported this season to 53 so far. Flu activity is likely to remain elevated for several more weeks.
CDC continues to recommend influenza vaccination for all persons 6 months of age and older as flu viruses are likely to continue circulating for weeks. In addition, in the context of widespread influenza activity, CDC is reminding clinicians and the public about the importance of prompt treatment with antiviral medications in people who are severely ill and people who are at high risk of serious flu complications who develop flu symptoms. Below is a summary of the key flu indicators for the week ending January 27, 2018 (week 4):
Influenza-like Illness Surveillance: For the week ending January 27, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 7.1%, which is above the national baseline of 2.2% and is the highest ILI percentage recorded since the 2009 pandemic. All 10 regions reported a proportion of outpatient visits for ILI at or above their region-specific baseline levels. ILI has been at or above the national baseline for 10 weeks so far this season. Over the past five seasons, ILI has remained at or above the baseline for 16 weeks on average.
Influenza-like Illness State Activity Indicator Map: New York City, the District of Columbia, and 42 states experienced high ILI activity (Alabama, Alaska, Arizona, Arkansas, Colorado, Connecticut, Florida, Georgia, Hawaii, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, Wisconsin and Wyoming). Puerto Rico and two states (California and Idaho) experienced moderate ILI activity. Three states experienced low ILI activity (Delaware, North Dakota and Washington). Three states experienced minimal ILI activity (Maine, Montana and Utah).
Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by Puerto Rico and 48 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin and Wyoming). Regional influenza activity was reported by Guam and one state (Oregon). Local influenza activity was reported by the District of Columbia and one state (Hawaii). Sporadic activity was reported by the U.S. Virgin Islands. Geographic spread data show how many areas within a state or territory are seeing flu activity.
Flu-Associated Hospitalizations: Since October 1, 2017, 14,676 laboratory-confirmed influenza-associated hospitalizations have been reported through the Influenza Hospitalization Network (FluSurv-NET), a population-based surveillance network for laboratory-confirmed influenza-associated hospitalizations. This translates to a cumulative overall rate of 51.4 hospitalizations per 100,000 people in the United States.
The highest hospitalization rate is among people 65 years and older (226.8 per 100,000), followed by adults aged 50-64 years (54.0 per 100,000), and younger children aged 0-4 years (33.3 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates, followed by children 0-4 years. Click for a flu guide for seniors.
During 2014-2015, hospitalization rates reported during week 4 for all ages were 43.5 per 100,000. During that same week, hospitalization rates for people 65 years and older were 213.8 per 100,000. Hospitalization rates for younger children 0-4 years were 40.2 per 100,000.
The proportion of deaths attributed to pneumonia and influenza (P&I) sharply increased again to 9.7% for the week ending January 13, 2018 (week 2). This percentage is above the epidemic threshold of 7.2% for week 2 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
17 influenza-associated pediatric deaths were reported to CDC during week 4.
Five deaths were associated with an influenza A(H3) virus and occurred during weeks 1, 2, 3 and 4 (the weeks ending January 6, January 13, January 20, and January 27, 2018). Two deaths were associated with an influenza A(H1N1)pdm09 virus and occurred during weeks 3 and 4 (the weeks ending January 20, 2018, and January 27, 2018, respectively). Four deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 3 and 4. Five deaths were associated with an influenza B virus and occurred during weeks 1, 3, and 4 (the week ending January 6, January 20, and January 27, 2018, respectively).
A total of 53 influenza-associated pediatric deaths for the 2017-2018 season have been reported to CDC.
One influenza-associated pediatric death that occurred during the past 2015-2016 flu season was reported to CDC during week 4.
This death was associated with an influenza A virus for which no subtyping was performed and occurred during week 28 (the week ending July 16, 2016). This death brings the total number of reported influenza-associated deaths occurring during that season to 93.
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending January 27 was 26.1%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 18.3% to 32.3%.
During the week ending January 27, of the 15,427 (26.1%) influenza-positive tests reported to CDC by clinical laboratories, 11,792 (76.4%) were influenza A viruses and 3,635 (23.6%) were influenza B viruses.
The most frequently identified influenza virus subtype reported by public health laboratories was influenza A(H3N2) virus.
During the week ending January 27, 1,280 (80.2%) of the 1,597 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 317 (19.8%) were influenza B viruses. Of the 1,206 influenza A viruses that were subtyped, 1,017 (84.3%) were H3N2 viruses and 189 (15.7%) were (H1N1)pdm09 viruses.
The majority of the influenza viruses collected from the United States during October 1, 2017 through January 27, 2018 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses.
Since October 1, 2017, CDC has tested 282 influenza A(H1N1)pdm09, 828 influenza A(H3N2), and 337 influenza B viruses for resistance to antiviral medications (i.e. oseltamivir, zanamivir, or peramivir). While the majority of the tested viruses showed susceptibility to the antiviral drugs, two (0.7%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but were sensitive to zanamivir.