CDC Flu Update: Seasonal Activity Continues to Increase

According to this week’s FluView report from the Centers for Disease Control and Prevention (CDC), seasonal influenza activity continues to increase in the United States. During week 46 (the week ending Nov. 18, 2017), several flu activity indicators were higher than is typically seen for this time of year. Two states reported widespread flu activity, six states reported regional flu activity and 20 states reported local influenza activity. Flu vaccine is the best available way to protect against influenza. CDC recommends that everyone 6 months and older get an injectable flu vaccine as soon as possible.

Influenza-like Illness Surveillance: For the week ending November 18, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 2.0% which is below the national baseline of 2.2%. Regions 1, 2, 4 and 6 reported a proportion of outpatient visits for ILI at or above their region-specific baseline level.

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: Two states experienced high ILI activity (Louisiana and Mississippi). One state experienced moderate ILI activity (Georgia). New York City and four states (Alabama, Nebraska, South Carolina, and Texas) experienced low ILI activity. The District of Columbia and 43 states experienced minimal ILI activity (Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Hawaii, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Dakota, Tennessee, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin and Wyoming).  Data were insufficient to calculate an ILI activity level from Puerto Rico. 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 two states (Louisiana and Oklahoma). Regional influenza activity was reported by Guam and six states (Arkansas, Georgia, Kentucky, Massachusetts, Mississippi, and South Carolina). Local influenza activity was reported by 20 states (Alabama, Alaska, Arizona, California, Colorado, Connecticut, Florida, Kansas, Maine, Maryland, Nebraska, New Hampshire, New Mexico, North Dakota, Ohio, Pennsylvania, Texas, Utah, Washington, and Wisconsin). Sporadic activity was reported by the District of Columbia, the U.S. Virgin Islands and 21 states (Delaware, Hawaii, Idaho, Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Montana, Nevada, New Jersey, New York, North Carolina, Oregon, Rhode Island, South Dakota, Tennessee, Vermont, Virginia, and Wyoming). No activity was reported by one state (West Virginia). Puerto Rico did not report. 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, 400 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 1.4 hospitalizations per 100,000 people in the United States.

The highest hospitalization rates are among people 65 years and older (5.1 per 100,000), followed by adults aged 50-64 years (1.7 per 100,000), and children younger than 5 years (1.0 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.

FluSurv-NET 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) was 5.6% for the week ending November 18, 2017 (week 44). This percentage is below the epidemic threshold of 6.4% for week 44 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:
Five influenza-associated pediatric deaths were reported to CDC during the week ending November 18.

Two deaths were associated with an influenza A (H3) virus and occurred during weeks 45 and 46 (the weeks ending November 11 and November 18, 2017, respectively). One death was associated with an influenza A (H1N1)pdm09 virus and occurred during week 44 (the week ending November 4, 2017). One death was associated with an influenza A virus for which no subtyping was performed and occurred during week 44.
Five influenza-associated pediatric deaths for the 2017-2018 season have been reported to CDC.

One death occurred during the 2016-2017 season and was associated with an influenza A (H3) virus and occurred during week 15 (the week ending April 15, 2017). This death brings the total number of reported influenza-associated pediatric deaths occurring during that season to 110.
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 November 18 was 5.3%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 1.1% to 7.3%.
During the week ending November 18, of the 832 (5.3%) influenza-positive tests reported to CDC by clinical laboratories, 616 (74.0%) were influenza A viruses and 216 (26.0%) were influenza B viruses.

The most frequently identified influenza virus type reported by public health laboratories was influenza A virus.

During the week ending November 18, 201 (83.4%) of the 241 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 40 (16.6%) were influenza B viruses. Of the 184 influenza A viruses that were subtyped, 157 (85.3%) were H3N2 viruses and 27 (14.7%) were (H1N1)pdm09 viruses.

The majority of the influenza viruses collected from the United States during May 21 through November 18, 2017 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses. None of the influenza viruses tested from May 21-November 18, 2017 were found to be resistant to antiviral medications (i.e. oseltamivir, zanamivir, or peramivir).

One human infection with a novel influenza A virus was reported during week 46.  This person was infected with an influenza A(H1N1) variant (H1N1v) virus and reported direct contact to swine during the week preceding illness onset.  No human-to-human transmission has been identified.  This is the first H1N1v virus infection detected in the United States in 2017.

Source: CDC