CDC Flu Update: Influenza-Like Illness Activity Similar to High-Severity Season of 2014-15

Influenza activity increased again in this week’s FluView report from the Centers for Disease Control and Prevention (CDC). All U.S. states but Hawaii continue to report widespread flu activity and the number of states experiencing “high” influenza activity increased from 26 plus New York City to 32 states plus New York City and Puerto Rico. Indicators used to track influenza-like-illness (ILI) activity are similar to what was seen during the peak of the 2014-2015 season, a season of high severity. The overall hospitalization rate is high also, but still lower than the overall hospitalization rate reported during the same week of the 2014-2015 season. CDC also is reporting an additional 10 flu-related pediatric deaths, bringing the total number of flu-related pediatric deaths reported this season to 30 so far. Flu activity is likely to continue 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 antiviral medications for treatment of influenza in people who are severely ill and people who are at high risk of serious flu complications.

Influenza-like Illness Surveillance: For the week ending January 13, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 6.3%, which is above the national baseline of 2.2% and is the highest ILI percentage recorded since the 2003-2004 season. 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 eight weeks so far this season. Over the past five seasons, ILI has remained at or above baseline for 16 weeks on average. Additional ILINet data, including national, regional, and select state-level data for the current and previous seasons, can be found at http://gis.cdc.gov/grasp/fluview/fluportaldashboard.html.

Influenza-like Illness State Activity Indicator Map: New York City, Puerto Rico and 32 states experienced high ILI activity (Alabama, Arizona, Arkansas, California, Florida, Georgia, Hawaii, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maryland, Mississippi, Missouri, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Oregon, South Carolina, South Dakota, Tennessee, Texas, Virginia, West Virginia, Wisconsin, and Wyoming). Nine states (Alaska, Colorado, Idaho, Iowa, Massachusetts, Minnesota, North Dakota, Pennsylvania, and Rhode Island) experienced moderate ILI activity. The District of Columbia and six states (Connecticut, Michigan, New Hampshire, Utah, Vermont, and Washington) experienced low ILI activity. Three states experienced minimal ILI activity (Delaware, Maine, and Montana). Additional data, including data for previous seasons, can be found at https://gis.cdc.gov/grasp/fluview/main.html

Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by Puerto Rico and 49 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, Oregon, 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. 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. Additional data are available at: https://gis.cdc.gov/grasp/fluview/FluView8.html.

Flu-Associated Hospitalizations: Since October 1, 2017, 8,990 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 31.5 hospitalizations per 100,000 people in the United States.
The highest hospitalization rates are among people 65 years and older (136.5 per 100,000), followed by adults aged 50-64 years (33.2 per 100,000), and children younger than 5 years (22.8 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates. During 2014-2015, hospitalization rates reported during week 2 for all ages were 36.3 per 100,000. During that same week, hospitalization rates for people 65 years and older were 176.1 per 100,000. Hospitalization rates for children younger than 5 years were 34.5 per 100,000.
Additional data, including hospitalization rates during other influenza seasons, can be found at http://gis.cdc.gov/GRASP/Fluview/FluHospRates.html and http://gis.cdc.gov/grasp/fluview/FluHospChars.html.

Mortality Surveillance:
The proportion of deaths attributed to pneumonia and influenza (P&I) was 8.2% for the week ending December 30, 2017 (week 52). This percentage is above the epidemic threshold of 7.1% for week 52 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
Region and state-specific data are available at https://gis.cdc.gov/grasp/fluview/mortality.html.

Pediatric Deaths:
Ten influenza-associated pediatric deaths were reported to CDC during week 2.
Four deaths were associated with an influenza A(H1N1)pdm09 virus and occurred during weeks 51, 1 and 2 (the weeks ending December 23, 2017, January 6, 2018, and January 13, 2018, respectively).  Three deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 44, 46, and 52 (the weeks ending November 4, 2017, November 18, 2017, and December 30, 2017, respectively).  Three deaths were associated with an influenza B virus and occurred during weeks 52, 1, and 2 (the weeks ending December 30, 2017, January 6, 2018, and January 13, 2018, respectively).
A total of 30 influenza-associated pediatric deaths for the 2017-2018 season have been reported to CDC.
Additional information on pediatric deaths is available on FluView Interactive at: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html.

Laboratory Data:
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending January 13 was 25.6%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 16.9% to 30.3%.
During the week ending January 13, of the 12,894 (25.6%) influenza-positive tests reported to CDC by clinical laboratories, 10,622 (82.4%) were influenza A viruses and 2,272 (17.6%) 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 13, 1,319 (87.5%) of the 1,507 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 188 (12.5%) were influenza B viruses. Of the 1,229 influenza A viruses that were subtyped, 1,111 (90.4%) were H3N2 viruses and 118 (9.6%) were (H1N1)pdm09 viruses.

The majority of the influenza viruses collected from the United States during October 1, 2017 through January 13, 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 168 influenza A(H1N1)pdm09, 587 influenza A(H3N2), and 209 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 (1.2%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but was sensitive to zanamivir.

Source: CDC