By Staff

Influenza activity increased again in this week’s FluView report. All U.S. states but Hawaii are reporting widespread flu activity. Indicators used to track influenza-like-activity (ILI) are similar to what was seen during the peak of the 2014-2015 season, a season of high severity. The overall hospitalization rate is high also, but still lower than the overall hospitalization rate reported during the same week of the 2014-2015 season. CDC also is reporting an additional 7 flu-related pediatric deaths, bringing the total number of flu-related pediatric deaths to 20 so far. Flu activity is likely to continue 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. In addition, in the context of widespread influenza activity, CDC is reminding clinicians and the public about the importance of antiviral medications for treatment of influenza in people who are severely ill and people who are at high risk of serious flu complications.

Below is a summary of the key flu indicators for the week ending January 6, 2018 (week 1):

Influenza-like Illness Surveillance: For the week ending January 6, the proportion of people seeing their health care provider for influenza-like illness (ILI) was 5.8%, which is above the national baseline of 2.2%. 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 seven weeks so far this season. During recent seasons, ILI has remained at or above baseline for 13 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 and 26 states experienced high ILI activity (Alabama, Arizona, Arkansas, California, Colorado, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, Nevada, New Jersey, New Mexico, Ohio, Oklahoma, Oregon, South Carolina, Texas, Virginia, Washington, West Virginia, and Wyoming). Puerto Rico and 10 states (Idaho, Massachusetts, Michigan, New York, North Carolina, Pennsylvania, Rhode Island, South Dakota, Tennessee, and Wisconsin) experienced moderate ILI activity. The District of Columbia and six states (Alaska, Hawaii, Iowa, Maryland, Minnesota, and Vermont) experienced low ILI activity. Eight states experienced minimal ILI activity (Connecticut, Delaware, Florida, Maine, Montana, New Hampshire, North Dakota, and Utah).

Geographic Spread of Influenza Viruses: Widespread influenza activity was reported by 49 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, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming). Regional influenza activity was reported by Guam and 1 state (Hawaii). Local influenza activity was reported by the District of Columbia. Sporadic activity was reported by the U.S. Virgin Islands. Puerto Rico did not report. Geographic spread data show how many areas within a state or territory are seeing flu activity.

Flu-Associated Hospitalizations: Since October 1, 2017, 6,486 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 22.7 hospitalizations per 100,000 people in the United States.

The highest hospitalization rates are among people 65 years and older (98.0 per 100,000), followed by adults aged 50-64 years (24.0 per 100,000), and children younger than 5 years (16.0 per 100,000). During most seasons, children younger than 5 years and adults 65 years and older have the highest hospitalization rates.

During 2014-2015, hospitalization rates reported during week 1 for all ages were 29.9 per 100,000. During that same week, hospitalization rates for people 65 years and older were 143.3 per 100,000. Hospitalization rates for children younger than 5 years were 30.0 per 100,000.

Mortality Surveillance:

The proportion of deaths attributed to pneumonia and influenza (P&I) was 7.0% for the week ending December 23, 2017 (week 51). This percentage is at the epidemic threshold of 7.0% for week 51 in the National Center

Pediatric Deaths:

Seven influenza-associated pediatric deaths were reported to CDC during week 1.

One death was associated with an influenza A(H3) virus and occurred during week 1 (the week ending January 6, 2018). One death was associated with an influenza A(H1N1)pdm09 virus and occurred during week 1. Two deaths were associated with an influenza A virus for which no subtyping was performed and occurred during week 1. Three deaths were associated with an influenza B virus and occurred during weeks 50 and 51 (the weeks ending December 16 and December 23, 2017, respectively).

A total of 20 influenza-associated pediatric deaths for the 2017-2018 season have been reported to CDC.

Laboratory Data:

Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending January 6 was 24.7%.

Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 13.3% to 32.1%.

During the week ending January 6, of the 10,320 (24.7%) influenza-positive tests reported to CDC by clinical laboratories, 8,628 (83.6%) were influenza A viruses and 1,692 (16.4%) 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 January 6, 1,202 (86.0%) of the 1,398 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 196 (14.0%) were influenza B viruses. Of the 1,153 influenza A viruses that were subtyped, 1,021 (88.6%) were H3N2 viruses and 132 (11.4%) were (H1N1)pdm09 viruses.

The majority of the influenza viruses collected from the United States during October 1, 2017 through January 6, 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 164 influenza A(H1N1)pdm09, 555 influenza A(H3N2), and 201 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, two (1.2%) H1N1pdm09 viruses were resistant to both oseltamivir and peramivir, but was sensitive to zanamivir.