According to this week’s FluView report, seasonal influenza activity increased and is elevated nationally in the United States. Based on flu surveillance data, CDC signaled the start of the 2018-2019 flu season. The proportion of people seeing their health care provider for influenza-like-illness (ILI) has been at or above the national baseline for four consecutive weeks (this means that there were excess visits to health care providers most likely caused by influenza.) Guam and six states (Alabama, California, Delaware, Georgia, Massachusetts, and New York) reported widespread flu activity and 37 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). Seven 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 nationally. However, in the most recent three weeks, influenza A(H3) viruses were most commonly reported in the southeastern region of the United States. One 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 15, 2018:
Influenza-like Illness Surveillance: For the week ending December 15 (week 50), the proportion of people seeing their health care provider for influenza-like illness (ILI) was 2.7%, which is above the national baseline if 2.2%. Eight of 10 regions (Regions 1, 2, 3, 4, 7, 8, 9 and 10) 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: Two states (Colorado and Georgia) experienced high ILI activity. New York City and nine states (Alabama, Arizona, Arkansas, Kentucky, Louisiana, Missouri, New Jersey, South Carolina, and Virginia) experienced moderate ILI activity. Puerto Ricco and 11 states (California, Massachusetts, Minnesota, Mississippi, New Mexico, New York, North Carolina, Oklahoma, Pennsylvania, Texas, and Utah) experienced low ILI activity. The District of Columbia and 28 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 Guam and 6 states (Alabama, California, Delaware, Georgia, Massachusetts, and New York). Regional influenza activity was reported by 18 states (Arizona, Connecticut, Florida, Idaho, Kentucky, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, North Carolina, Ohio, Oregon, Pennsylvania, Rhode Island, Texas, Vermont, and Virginia). Local influenza activity was reported by 19 states (Arkansas, Colorado, Illinois, Indiana, Iowa, Kansas, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Montana, North Dakota, Oklahoma, South Carolina, Tennessee, Utah, and Wyoming). Sporadic influenza activity was reported by the District of Columbia, Puerto Rico, the U.S. Virgin Islands and seven states (Alaska, Hawaii, Maine, South Dakota, Washington, West Virginia, and Wisconsin). 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, 835 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 2.9 hospitalizations per 100,000 people in the United States.
The highest hospitalization rate is among children younger than 5 years (7.7 per 100,000) followed by adults aged 65 years and older (6.6 per 100,000), and adults aged 50-64 years (3.4 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 6.0% during the week ending December 8, 2018 (week 49). This percentage is below the epidemic threshold of 6.7% for week 49 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 50 (the week ending December 15, 2018).
This death was associated with an influenza A virus for which no subtyping was performed and occurred during week 49 (the week ending December 8, 2018).
A total of seven 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 15 was 11.0%.
Regionally, the three-week average percent of specimens testing positive for influenza in clinical laboratories ranged from 2.7% to 14.7%.
During the week ending December 15, of the 2,666 (11.0%) influenza-positive tests reported to CDC by clinical laboratories, 2,522 (94.6%) were influenza A viruses and 144 (5.4%) 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 15, 399 (97.8%) of the 408 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 9 (2.2%) were influenza B viruses. Of the 376 influenza A viruses that were subtyped, 68 (18.1%) were H3N2 viruses and 308 (81.9%) were (H1N1)pdm09 viruses.
The majority of the influenza viruses collected from the United States during September 30, 2018 through December 15, 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 15, 2018 were found to be resistant to oseltamivir, zanamivir, or peramivir.