CDC Flu Report: Influenza A(H3) Reported More Frequently


According to this week’s FluView report, overall influenza activity remains elevated and is similar to activity reported last week. 48 states and Puerto Rico continue to report widespread flu activity and 32 states are experiencing high influenza-like-illness (ILI) activity levels. While cumulatively influenza A(H1N1)pdm09 viruses remain predominant for this flu season, during the weekend ending March 2, influenza A(H3) were reported more frequently nationally for the second week. Severity indicators continue to increase as expected but remain substantially lower than what was observed last season. This week another eight flu-related pediatric deaths occurring during the 2018-2019 season were reported to CDC, bringing the total to 64 flu-related deaths for the season.

CDC expects flu activity to remain elevated for a number of weeks. 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 March 2, 2019:

Influenza-like Illness Surveillance: For the week ending March 2 (week 9), the proportion of people seeing their health care provider for influenza-like illness (ILI) slightly decreased to 4.7%, but remains 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.
For comparison purposes, 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).
Additional ILINet data, including national, regional, and select state-level data for the current and previous seasons, can be found at
Influenza-like Illness (ILI) State Activity Indicator Map: The number of states experiencing high ILI activity slightly decreased from 33 states plus New York City last week to 32 states this week. Additional data, including data for previous seasons, can be found at
Geographic Spread of Influenza Viruses: The number of jurisdictions reporting widespread influenza activity slightly decreased from Puerto Rico and 49 states to Puerto Rico and 48 states. Geographic spread data reflect how many areas within a state or territory are seeing flu activity. Additional data are available at:

Flu-Associated Hospitalizations: Since October 1, 2018, 10,567 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 covering approximately 9% of the U.S. This translates to a cumulative overall rate of 36.6 hospitalizations per 100,000 people in the United States.
The highest hospitalization rate is among adults aged 65 years and older (107.7 per 100,000) followed by children younger than 5 years (49.3 per 100,000), and adults aged 50-64 years (48.4 per 100,000). During most seasons, adults 65 years and older have the highest hospitalization rates, followed by young children.
For comparison purposes:
The final, cumulative overall hospitalization rate for week 9 last season was 87.5 per 100,000.
Over the past 5 seasons, cumulative end-of-season hospitalization rates have ranged from 31.4 per 100,000 (2015-2016) to 102.9 per 100,000 (2017-2018).
Additional data, including hospitalization rates during previous influenza seasons, can be found at and
FluSurv-Net data is used to generate national estimates of the total numbers of flu cases, medical visits, and hospitalizations. This season, CDC is reporting preliminary cumulative in-season estimates, which are available at

Mortality Surveillance: The proportion of deaths attributed to pneumonia and influenza (P&I) was 7.5% during the week ending February 23, 2019 (week 8). This percentage is above the epidemic threshold of 7.3% for week 8 in the National Center for Health Statistics (NCHS) Mortality Surveillance System. P&I has been at or above threshold for a total of 6 weeks this season: four consecutive weeks (weeks 1-4), followed by 2 weeks below the threshold, and for the most recent two weeks (weeks 7 and 8) P&I is again above the threshold.
For comparison purposes, over the last five seasons, P&I has been at or above epidemic threshold for a range of four weeks (2015-2016) to 16 weeks (2017-2018).
Additional P&I mortality data for current and past seasons and by geography (national, HHS region, or state) are available at

Pediatric Deaths: Nine influenza-associated pediatric deaths were reported to CDC during week 9 (the week ending March 2, 2019), eight of which occurred during the 2018-2019 influenza season.
Four deaths were associated with an influenza A(H1N1)pdm09 virus and occurred during weeks 7, 8 and 9 (the weeks ending February 16, February 23 and March 2, 2019, respectively). One death was associated with an influenza A(H3) virus and occurred during week 9. Two deaths were associated with an influenza A virus for which no subtyping was performed and occurred during weeks 6 and 9 (the weeks ending February 9 and March 2, 2019). One death was associated with an influenza B virus and occurred during week 6. A total of 64 influenza-associated pediatric deaths have been reported for the 2018-2019 season.
An additional death that occurred during the 2015-2016 season was reported to CDC this week. This death was associated with an influenza A virus for which no subtyping was performed and brings the total number of reported influenza-associated deaths occurring during that season to 95.
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: 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 March 2 was 26.1%, a slight increase from 25.9% the prior week.
For comparison purposes, since laboratory data from clinical and public health laboratories was disaggregated three seasons ago, the peak percent of respiratory specimens testing positive for flu at clinical laboratories has ranged from 23.6% to 27.4%.
Nationally, during the week ending March 2, influenza A(H3) viruses were reported more frequently than influenza A(H1N1)pdm09 viruses and have been predominant for the last three weeks in Regions 2, 4, 6, 7 and 8. However, cumulatively, influenza A(H1N1)pdm09 viruses are still predominant nationally for the 2018-2019 season.

The majority of the influenza viruses collected from the United States during September 30, 2018, through March 2, 2019, were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses.
The vast majority (>99%) of influenza viruses tested showed susceptibility to oseltamivir, zanamivir and peramivir. This week, no new viruses with reduced susceptibility to antiviral drugs were reported. So far this season, two (0.1%) influenza A(H1N1)pdm09 viruses displayed highly reduced inhibition by oseltamivir and peramivir.  An additional two (0.1%) influenza A(H1N1)pdm09 viruses showed reduced inhibition by oseltamivir. All influenza viruses tested showed susceptibility to zanamivir.

Source: CDC

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