CDC Flu Update: Widespread Activity Continues

Influenza activity increased again according to the latest FluView report from the Centers for Disease Control and Prevention (CDC). 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 42 states plus New York City and the District of Columbia to 43 states plus New York City, the District of Columbia and Puerto Rico. ILI has reached 7.7% this week and is the highest level of ILI recorded since the 2009 H1N1 pandemic, which peaked at 7.7% ILI. The overall hospitalization rate is higher than the overall hospitalization rate reported for the same week of 2014-2015; a high severity, H3N2-predominant season. CDC also is reporting an additional 10 flu-related pediatric deaths during week 5, bringing the total number of flu-related pediatric deaths reported this season to 63. 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 and there is an increasing proportion of influenza B and H1N1 viruses being detected. 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 February 3, 2018 (week 5):

Influenza-like Illness Surveillance: For the week ending February 3, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 7.7%, 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 11 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, the District of Columbia, Puerto Rico and 43 states experienced high ILI activity (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, 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). Three states (Hawaii, Idaho, and Washington) experienced moderate ILI activity. Two states experienced low ILI activity (North Dakota and Utah). Two states experienced minimal ILI activity (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 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 Hawaii and Oregon. Local influenza activity was reported by the District of Columbia and Guam. 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, 17,101 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 59.9 hospitalizations per 100,000 people in the United States. The highest hospitalization rate is among people 65 years and older (263.6 per 100,000), followed by adults aged 50-64 years (63.1 per 100,000), and younger children aged 0-4 years (40.0 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates, followed by children 0-4 years. During the 2014-2015 season, the cumulative overall hospitalization rate reported during week 5 was 44.1 per 100,000. During that same week, hospitalization rates for people 65 years and older were 217.3 per 100,000. Hospitalization rates for younger children 0-4 years were 40.4 per 100,000. 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. 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) is high again at 10.1% for the week ending January 20, 2018 (week 3). This percentage is above the epidemic threshold of 7.3% for week 3 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 5.
Four deaths were associated with an influenza A(H3) virus and occurred during weeks 3 and 4 (the weeks ending January 20, and January 27, 2018, respectively). Three deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 52, 4, and 5 (the weeks ending December 30, 2017, January 27, and February 3, 2017, respectively). Three deaths were associated with an influenza B virus and occurred during weeks 2 and 4 (the weeks ending January 13, and January 27, 2018, respectively. A total of 63 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 February 3 was 26.3%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 15.2% to 30.6%.
During the week ending February 3, of the 16,641 (26.3%) influenza-positive tests reported to CDC by clinical laboratories, 11,517 (69.2%) were influenza A viruses and 5,124 (30.8%) 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 February 3, 1,065 (73.3%) of the 1,453 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 388 (26.7%) were influenza B viruses. Of the 978 influenza A viruses that were subtyped, 834 (85.3%) were H3N2 viruses and 144 (14.7%) were (H1N1)pdm09 viruses. The majority of the influenza viruses collected from the United States during October 1, 2017 through February 3, 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 376 influenza A(H1N1)pdm09, 903 influenza A(H3N2), and 387 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, four (1.1%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but was sensitive to zanamivir.

Source: CDC