CDC Flu Update: Influenza-Like Illness Increasing Sharply

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. The proportion of people seeing their healthcare provider for influenza-like-illness (ILI) increased sharply from last week and has been at or above the national baseline for three weeks so far this season. Influenza A(H3N2) viruses were most commonly reported during week 49 (the week ending Dec. 9, 2017) and have been the predominant virus so far this season. Several flu activity indicators are higher than is typically seen for this time of year. Twelve states reported widespread flu activity, 26 states reported regional flu activity and 10 states reported local influenza activity. A 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 9, the proportion of people seeing their healthcare provider for influenza-like illness (ILI) was 2.7% which is above the national baseline of 2.2%. Seven of 10 regions (regions 1, 2, 4, 5, 6, 7 and 9) 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: Four states experienced high ILI activity (Louisiana, Mississippi, South Carolina, and Texas). Five states (Alabama, Alaska, Arizona, Georgia, and Kentucky) experienced moderate ILI activity. New York City, Puerto Rico and 16 states (Arkansas, California, Colorado, Hawaii, Indiana, Kansas, Massachusetts, Minnesota, Missouri, Nebraska, Nevada, Oklahoma, Oregon, South Dakota, Virginia, and Wyoming) experienced low ILI activity. 25 states experienced minimal ILI activity (Connecticut, Delaware, Florida, Idaho, Illinois, Iowa, Maine, Maryland, Michigan, Montana, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Pennsylvania, Rhode Island, Tennessee, Utah, Vermont, Washington, West Virginia, and Wisconsin). Data was insufficient to calculate an ILI activity from the District of Columbia. Additional data, including data for previous seasons, can be found at

Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by 12 states (Arkansas, California, Connecticut, Louisiana, Massachusetts, Mississippi, Missouri, New York, Ohio, Oklahoma, Virginia, and Wisconsin). Regional influenza activity was reported by Puerto Rico and 26 states (Alabama, Alaska, Arizona, Colorado, Florida, Georgia, Idaho, Illinois, Kansas, Kentucky, Maine, Maryland, Minnesota, Montana, Nebraska, New Hampshire, New Jersey, New Mexico, North Dakota, Oregon, Rhode Island, South Carolina, Tennessee, Texas, Washington, and Wyoming). Local influenza activity was reported by 10 states (Delaware, Hawaii, Indiana, Iowa, Michigan, North Carolina, Pennsylvania, South Dakota, Vermont, and West Virginia). Sporadic activity was reported by the District of Columbia, the U.S. Virgin Islands and two states (Nevada and Utah). 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, 1,232 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 4.3 hospitalizations per 100,000 people in the United States.
The highest hospitalization rates are among people 65 years and older (17.3 per 100,000), followed by adults aged 50-64 years (4.5 per 100,000), and children younger than 5 years (3.5 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates. 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 5.5% for the week ending November 25, 2017 (week 47). This percentage is below the epidemic threshold of 6.6% for week 47 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
Region and state-specific data are available at

Pediatric Deaths:
One influenza-associated pediatric death was reported to CDC during week 49.
This death was associated with an influenza A virus for which no subtyping was performed and occurred during week 44 (the week ending November 4, 2017).
A total of 8 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 9 was 8.4%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 2.7% to 11.8%.
During the week ending December 9, of the 1,633 (8.4%) influenza-positive tests reported to CDC by clinical laboratories, 1,343 (82.2%) were influenza A viruses and 290 (17.8%) 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 9, 500 (89.0%) of the 562 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 62 (11.0%) were influenza B viruses. Of the 490 influenza A viruses that were subtyped, 464 (94.7%) were H3N2 viruses and 26 (5.3%) were (H1N1)pdm09 viruses.

The majority of the influenza viruses collected from the United States during October 1 through December 9, 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 9, 2017, none 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 by Iowa during the week ending December 9. The person was infected with an influenza A(H3N2) variant [A(H3N2)v] virus and reported direct contact with swine during the week preceding illness onset. No human-to-human transmission has been identified.

Source: CDC