CDC Flu Update: Influenza-Like Illness Consultations Rise Above Baseline

According to this week’s FluView report from the Centers for Disease Control and Prevention (CDC), seasonal influenza activity increased in the United States. The proportion of people seeing their healthcare provider for influenza-like-illness (ILI) is above the national baseline for the first time this season. Influenza A(H3N2) viruses were most commonly reported during week 47 (the week ending Nov. 25, 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. Four states reported widespread flu activity, ten states reported regional flu activity and 24 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 25, 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%. This increase in the percentage of patient visits for ILI during week 47 might be influenced in part by a reduction in routine health care visits during the holidays, as has occurred in previous seasons.  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). One state experienced moderate ILI activity (Georgia). Ten states (Alabama, Alaska, Arizona, Hawaii, Massachusetts, Nebraska, Oklahoma, South Dakota, Texas, and Virginia) experienced low ILI activity. The District of Columbia, New York City, and 36 states experienced minimal ILI activity (Arkansas, California, Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, 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). Data was insufficient to calculate an ILI activity level from Puerto Rico. Additional data, including data for previous seasons, can be found at

Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by four states (Georgia, Louisiana, Massachusetts, and Oklahoma). Regional influenza activity was reported by Guam and ten states (Arkansas, Connecticut, Kentucky, Maine, Mississippi, New Hampshire, North Dakota, Oregon, South Carolina, and Washington). Local influenza activity was reported by Puerto Rico and 24 states (Alabama, Alaska, Arizona, California, Colorado, Florida, Hawaii, Illinois, Kansas, Maryland, Minnesota, Missouri, Nebraska, New Jersey, New Mexico, New York, Ohio, Pennsylvania, South Dakota,  Tennessee, Texas, Utah, Wisconsin, and Wyoming). Sporadic activity was reported by the District of Columbia, the U.S. Virgin Islands and 12 states (Delaware, Idaho, Indiana, Iowa, Michigan, Montana, Nevada, North Carolina, Rhode Island, Vermont, Virginia, and West Virginia). No activity was reported by one state (West Virginia. Guam, Puerto Rico, and one state (Nebraska). 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, 566 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 2.0 hospitalizations per 100,000 people in the United States. The highest hospitalization rates are among people 65 years and older (7.3 per 100,000), followed by adults aged 50-64 years (2.4 per 100,000), and children younger than 5 years (1.6 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 and

Mortality Surveillance:
The proportion of deaths attributed to pneumonia and influenza (P&I) was 5.7% for the week ending November 11, 2017 (week 45). This percentage is below the epidemic threshold of 6.5% for week 45 in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
Region and state-specific data are available at

Pediatric Deaths:
No influenza-associated pediatric deaths were reported to CDC during week 47.
Five 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 November 25 was 7.2%.
Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 1.9% to 8.6%.

During the week ending November 25, of the 1,051 (7.2%) influenza-positive tests reported to CDC by clinical laboratories, 795 (75.6%) were influenza A viruses and 256 (24.4%) 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 25, 186 (88.6%) of the 210 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 24 (11.4%) were influenza B viruses. Of the 186 influenza A viruses that were subtyped, 168 (90.3%) were H3N2 viruses and 18 (9.7%) were (H1N1)pdm09 viruses.

The majority of the influenza viruses collected from the United States during October 1 through November 25, 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-November 25, 2017, none were found to be resistant to antiviral medications (i.e. oseltamivir, zanamivir or peramivir).

Source: CDC