CDC Flu Update: Seasonal Flu Activity Increasing Slightly

According to this week’s FluView report from the Centers for Disease Control and Prevention (CDC), seasonal influenza activity increased slightly in the United States. The proportion of people seeing their healthcare provider for influenza-like-illness (ILI) has been at or above the national baseline for two weeks this season. Influenza A(H3N2) viruses were most commonly reported during week 48 (the week ending Dec. 2, 2017) and have been the predominant virus so far this season. Several flu activity indicators were higher than is typically seen for this time of year. Seven states reported widespread flu activity, 18 states reported regional flu activity and 18 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 December 2, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 2.3% which is above the national baseline of 2.2%. Regions 1, 4, 6 and 7 reported a proportion of outpatient visits for ILI at or above their region-specific baseline levels. Additional ILINet data, including national, regional, and select state-level data for the current and previous seasons, can be found at

Influenza-like Illness State Activity Indicator Map: Three states experienced high ILI activity (Louisiana, Mississippi, and South Carolina). Puerto Rico and 3 states (Georgia, Hawaii, and Texas) experienced moderate ILI activity. The District of Columbia and six states (Alabama, Alaska, Arkansas, Oklahoma, South Dakota, and Virginia) experienced low ILI activity. New York City and 38 states experienced minimal ILI activity (Arizona, California, Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oregon, Pennsylvania, Rhode Island, Tennessee, Utah, Vermont, Washington, West Virginia, Wisconsin, and Wyoming). Additional data, including data for previous seasons, can be found at

Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by seven states (Arkansas, Georgia, Louisiana, Massachusetts, Mississippi, Oklahoma, and Virginia). Regional influenza activity was reported by Puerto Rico and 18 states (Alabama, Alaska, Arizona, California, Colorado, Connecticut, Florida, Illinois, Kentucky, Maine, Missouri, New Hampshire, New York, North Dakota, Ohio, South Carolina, Texas, and Washington). Local influenza activity was reported by 18 states (Hawaii, Idaho, Indiana, Kansas, Maryland, Michigan, Minnesota, Montana, Nebraska, New Jersey, New Mexico, North Carolina, Oregon, Pennsylvania, South Dakota, Tennessee, Wisconsin, and Wyoming). Sporadic activity was reported by the District of Columbia, the U.S. Virgin Islands and seven states (Delaware, Iowa, Nevada, Rhode Island, Utah, Vermont, and West Virginia). Guam did not report. Geographic spread data show how many areas within a state or territory are seeing flu activity. Additional data are available at:

Flu-Associated Hospitalizations: Since October 1, 2017, 856 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 3.0 hospitalizations per 100,000 people in the United States.
The highest hospitalization rates are among people 65 years and older (11.5 per 100,000), followed by adults aged 50-64 years (3.3 per 100,000), and children younger than 5 years (2.7 per 100,000). Additional data, including hospitalization rates during other influenza seasons, can be found at and

Mortality Surveillance:
The proportion of deaths attributed to pneumonia and influenza (P&I) was 5.7% for the week ending November 18, 2017 (week 46). This percentage is below the epidemic threshold of 6.6% for week 46 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
Region and state-specific data are available at

Pediatric Deaths:
Two influenza-associated pediatric deaths were reported to CDC during week 48.
One death was associated with an influenza A (H3) virus and occurred during week 45 (the week ending November 11, 2017). One death was associated with an influenza B virus and occurred during week 47 (the week ending November 25, 2017).
Seven 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:

Laboratory Data:
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending December 2 was 6.7%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 2.0% to 9.0%.
During the week ending December 2, of the 1,354 (6.7%) influenza-positive tests reported to CDC by clinical laboratories, 1,033 (76.3%) were influenza A viruses and 321 (23.7%) were influenza B viruses.

The most frequently identified influenza virus type reported by public health laboratories was influenza A virus.
During the week ending December 2, 359 (84.5%) of the 425 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 66 (15.5%) were influenza B viruses. Of the 347 influenza A viruses that were subtyped, 314 (90.5%) were H3N2 viruses and 33 (9.5%) were (H1N1)pdm09 viruses.

The majority of the influenza viruses collected from the United States during October 1 through December 2, 2017 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2017–18 Northern Hemisphere influenza vaccine viruses. Of the influenza viruses tested and collected during October 1-December 2, 2017, none were found to be resistant to antiviral medications (i.e. oseltamivir, zanamivir, or peramivir).

Source: CDC