According to this week’s FluView report, while parts of the country are seeing elevated flu activity, overall activity nationally remains low. The proportion of people seeing their health care provider for influenza-like-illness (ILI) has been at the national baseline for three consecutive weeks. (This means that there were excess visits to health care providers most likely caused by influenza.) Three states (California, Georgia, and Massachusetts) reported widespread flu activity and 31 states are now reporting regional or local flu activity. That means those states are seeing outbreaks of flu and laboratory-confirmed flu in at least half of the regions of the state (widespread activity), in at least two regions but less than half of the regions of the state (regional activity), and in a single region (local activity). However 16 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands continue to report only sporadic flu activity, which means those states are seeing small numbers of flu or one laboratory-confirmed flu outbreak. Influenza A(H1N1)pdm09 viruses have been the most commonly identified flu viruses since September 30, 2018. CDC analyzes flu surveillance data every week and declares the start of each “flu season” after sustained elevated activity is observed across key flu indicators for a number of weeks. Based on flu surveillance data, it’s too early to say the 2018-2019 flu season has started nationally. Despite this, an additional flu-associated pediatric death occurring during the 2018-2019 season is also being reported this week.
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. For anyone 6 months or older who has not yet been vaccinated this season, CDC recommends that they get vaccinated now. Below is a summary of the key flu indicators for the week ending December 8, 2018:
Influenza-like Illness Surveillance: For the week ending December 8 (week 49), the proportion of people seeing their health care provider for influenza-like illness (ILI) was 2.2%, which is at the national baseline. Five of 10 regions (Regions 1, 2, 4, 7, and 8) 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: One state (Georgia) experienced high ILI activity. Puerto Rico and four states (Colorado, Connecticut, Kentucky, and Louisiana) experienced moderate ILI activity. New York City, the District of Columbia and nine states (Alabama, Arizona, Mississippi, Missouri, New Jersey, Oklahoma, South Carolina, Utah and Virginia) experienced low ILI activity. 36 states 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 three state (California, Georgia, and Massachusetts). Regional influenza activity was reported by 10 states (Arizona, Connecticut, Idaho, Kentucky, Nevada, New York, North Carolina, Rhode Island, Texas, and Vermont). Local influenza activity was reported by 21 states (Alabama, Colorado, Delaware, Florida, Illinois, Kansas, Louisiana, Maryland, Michigan, Minnesota, Montana, Nebraska, New Jersey, New Mexico, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, Tennessee, and Utah). Sporadic influenza activity was reported by the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 16 states (Alaska, Arkansas, Hawaii, Indiana, Iowa, Maine, Mississippi, Missouri, New Hampshire, North Dakota, South Dakota, Virginia, Washington, West Virginia, Wisconsin, and Wyoming). 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, 544 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. This translates to a cumulative overall rate of 1.9 hospitalizations per 100,000 people in the United States.
The highest hospitalization rate is among children younger than 5 years (5.0 per 100,000) followed by adults aged 65 years and older (4.6 per 100,000), and adults aged 50-64 years (2.1 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 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 6.0% during the week ending December 1, 2018 (week 48). This percentage is below the epidemic threshold of 6.6% for week 48 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: One influenza-associated pediatric death was reported to CDC during week 49 (the week ending December 8, 2018).
This death was associated with an influenza B virus and occurred during week 48 (the week ending December 1, 2018).
A total of six 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.
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending December 8 was 3.6%.
Regionally, the three-week average percent of specimens testing positive for influenza in clinical laboratories ranged from 1.6% to 8.1%.
During the week ending December 8, of the 665 (3.6%) influenza-positive tests reported to CDC by clinical laboratories, 613 (92.2%) were influenza A viruses and 52 (7.8%) 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 8, 196 (94.7%) of the 207 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 11 (5.3%) were influenza B viruses. Of the 183 influenza A viruses that were subtyped, 35 (19.1%) were H3N2 viruses and 148 (80.9%) were (H1N1)pdm09 viruses.
The majority of the influenza viruses collected from the United States during September 30, 2018 through December 8, 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 8, 2018 were found to be resistant to oseltamivir, zanamivir, or peramivir.