CDC Flu Update: Activity is Increasing

January 8, 2019

According to this week’s FluView report, seasonal influenza activity continues to increase. The number of states experiencing high influenza activity went from nine states plus New York City during the last reporting week to 19 states plus New York City and the number of states reporting widespread geographic flu activity went from 11 states to 24 states. CDC also reported another two flu-associated pediatric deaths. Nationally, the proportion of people seeing their health care provider for influenza-like-illness (ILI) has been at or above the baseline for six consecutive weeks. By this measure, the past five flu seasons have lasted between 11 and 20 weeks with an average of 16 weeks. H1N1 viruses have been the most commonly identified flu viruses nationally. However, H3N2 viruses have predominated in the southeastern region of the United States.

An annual flu vaccine is the best way to protect against influenza and its potentially serious complications. There are many benefits to vaccination, including reducing the risk of flu illness, doctor’s visits, hospitalization, and even death in children. Flu vaccination also has been shown to reduce severity of illness among people who get vaccinated but still get sick. For anyone 6 months or older who has not yet been vaccinated this season, CDC recommends that they get vaccinated now. There also are flu antiviral drugs that can be used to treat flu illness. Below is a summary of the key flu indicators for the week ending December 29, 2018:

Influenza-like Illness Surveillance: For the week ending December 29 (week 52), the proportion of people seeing their health care provider for influenza-like illness (ILI) was 4.1%, which is above the national baseline of 2.2%. Over the past five flu seasons, the peak percent of visits due to ILI has ranged between 3.6% (2015-2016) and 7.5% (2017-2018). All 10 regions 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: New York City and 19 states (Alabama, Arizona, Colorado, Georgia, Illinois, Indiana, Kansas, Kentucky, Louisiana, Massachusetts, Mississippi, Nevada, New Jersey, New Mexico, Oklahoma, South Carolina, Texas, Utah, and Virginia) experienced high ILI activity. Nine states (Arkansas, California, Michigan, Missouri, New York, North Carolina, Pennsylvania, Rhode Island, and Vermont) experienced moderate ILI activity. The District of Columbia and 10 states (Connecticut, Florida, Iowa, Minnesota, Montana, Nebraska, Ohio, Oregon, Wisconsin, and Wyoming) experienced low ILI activity. Puerto Rico and 12 states (Alaska, Delaware, Hawaii, Idaho, Maine, Maryland, New Hampshire, North Dakota, South Dakota, Tennessee, Washington, and West Virginia) experienced minimal ILI activity. 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 Guam and 24 states (Alabama, Arizona, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Indiana, Kentucky, Louisiana, Massachusetts, Nebraska, New Jersey, New Mexico, New York, North Carolina, Pennsylvania, Rhode Island, South Carolina, Utah, Vermont, and Virginia). Regional influenza activity was reported by Puerto Rico and 18 states (Arkansas, Illinois, Iowa, Kansas, Michigan, Missouri, Montana, Nevada, New Hampshire, North Dakota, Ohio, Oklahoma, Oregon, South Dakota, Tennessee, Texas, West Virginia, and Wyoming). Local influenza activity was reported by six states (Maine, Maryland, Minnesota, Mississippi, Washington, and Wisconsin). Sporadic influenza activity was reported by the District of Columbia, the U.S. Virgin Islands and two states (Alaska and Hawaii). 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: https://gis.cdc.gov/grasp/fluview/FluView8.html.

Flu-Associated Hospitalizations: Since October 1, 2018, 1,562 laboratory-confirmed influenza-associated hospitalizations have now been reported through the Influenza Hospitalization Network (FluSurv-NET), a population-based surveillance network for laboratory-confirmed influenza-associated hospitalizations covering approximately 9% of the U.S. This translates to a cumulative overall rate of 5.4 hospitalizations per 100,000 people in the United States.
The highest hospitalization rate is among children younger than 5 years (14.5 per 100,000) followed by adults aged 65 years and older (11.9) per 100,000), and adults aged 50-64 years (6.2 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates followed by young children.
Additional data, including hospitalization rates during previous 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 6.1% during the week ending December 22, 2018 (week 51). This percentage is below the epidemic threshold of 6.9% for week 51 in the National Center for Health Statistics (NCHS) Mortality Surveillance System. Additional P&I mortality data for current and past seasons and by geography (national, HHS region, or state) are available at https://gis.cdc.gov/grasp/fluview/mortality.html

Pediatric Deaths: Two influenza-associated pediatric deaths were reported to CDC during week 52 (the week ending December 29, 2018).
Both deaths were associated with influenza A(H1N1)pdm09 virus infections and occurred during weeks 51 and 52 (the weeks ending December 22 and December 29, 2018).
A total of 13 influenza-associated pediatric deaths have been reported for the 2018-2019 season.
Additional information on influenza-associated pediatric deaths reported during past seasons, including basic demographics, underlying conditions, bacterial co-infections, and place of death is available on FluView Interactive at: https://gis.cdc.gov/GRASP/Fluview/PedFluDeath.html. More detailed information about pediatric deaths reported during the current season will be available later in the season.

Laboratory Data:
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending December 29 was 13.7%.
Regionally, the three-week average percent of specimens testing positive for influenza in clinical laboratories ranged from 6.5% to 19.5%.
During the week ending December 29, of the 3,636 (13.7%) influenza-positive tests reported to CDC by clinical laboratories, 3,532 (97.1%) were influenza A viruses and 104 (2.9%) were influenza B viruses.
The most frequently identified influenza virus type reported by public health laboratories was influenza A(H1N1)pdm09 virus.
During the week ending December 29, 522 (97.4%) of the 536 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 14 (2.6%) were influenza B viruses. Of the 491 influenza A viruses that were subtyped, 52 (10.6%) were H3N2 viruses and 439 (89.4%) were (H1N1)pdm09 viruses.
The majority of the influenza viruses collected from the United States during September 30, 2018 through December 29, 2018 were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses.
None of the viruses tested from September 30-December 29, 2018 were found to be resistant to oseltamivir, zanamivir, or peramivir.

Source: CDC