CDC Flu Update: Influenza A H1N1 Viruses Most Commonly Identified


According to this week’s FluView report, overall flu activity remains low nationally. While four states (Massachusetts, New Hampshire, North Dakota, and Oregon) are now reporting local flu activity; 42 states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands continue to report only sporadic flu activity. Influenza A H1N1 viruses have been the most commonly identified flu viruses in the last three 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. There are many vaccine options. CDC recommends that everyone 6 months and older get vaccinated by the end of October. Below is a summary of the key flu indicators for the week ending Oct. 20, 2018:

Influenza-like Illness Surveillance: For the week ending October 20 (week 42), the proportion of people seeing their health care provider for influenza-like illness (ILI) was 1.5% and remains below the national baseline of 2.2%. All 10 regions reported a proportion of outpatient visits for ILI below their region-specific baseline levels. Additional ILINet data, including national, regional, and select state-level data for the current and previous seasons, can be found at

Influenza-like Illness State Activity Indicator Map: Puerto Rico and one state (Georgia) experienced low ILI activity. New York City, the District of Columbia, and 49 states experienced minimal ILI activity. Additional data, including data for previous seasons, can be found at
Geographic Spread of Influenza Viruses: Local influenza activity was reported by 4 states (Massachusetts, New Hampshire, North Dakota, and Oregon). Sporadic activity was reported by the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 42 states (Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Washington, West Virginia, Wisconsin, and Wyoming). No influenza activity was reported by 4 states (Illinois, Mississippi, Rhode Island, and Virginia). 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:

Flu-Associated Hospitalizations:
Reporting of influenza-associated hospitalization data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) for the 2018-2019 influenza season will begin later this season. Additional data, including hospitalization rates during previous influenza seasons, can be found at and

Mortality Surveillance:
The proportion of deaths attributed to pneumonia and influenza (P&I) was 5.3% during the week ending October 13, 2018 (week 41). This percentage is below the epidemic threshold of 5.9% for week 41 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

Pediatric Deaths:
No influenza-associated pediatric deaths were reported to CDC during week 42. One influenza-associated pediatric death for the 2018-2019 season has been reported to CDC (during week 41). Additional information on influenza-associated pediatric deaths including basic demographics, underlying conditions, bacterial co-infections, and place of death for the current and past seasons, pediatric deaths is available on FluView Interactive at:

Laboratory Data:
Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending October 20 was 0.6%. Regionally, the three week average percent of specimens testing positive for influenza in clinical laboratories ranged from 0.2% to 4.3%. During the week ending October 20, of the 76 (0.6%) influenza-positive tests reported to CDC by clinical laboratories, 47 (61.8%) were influenza A viruses and 29 (38.2%) were influenza B viruses. The most frequently identified influenza virus type reported by public health laboratories was influenza A virus. During the week ending October 20, 41 (77.4%) of the 53 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 12 (22.6%) were influenza B viruses. Of the 27 influenza A viruses that were subtyped, 6 (22.2%) were H3N2 viruses and 21 (77.8%) were (H1N1)pdm09 viruses. The majority of the influenza viruses collected from the United States during May 20 through October 20, 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 May 20-October 20, 2018 were found to be resistant to oseltamivir, zanamivir, or peramivir. Antiviral resistance data will be updated weekly starting later in the season.

Source: CDC

Related Videos
Jill Holdsworth, MS, CIC, FAPIC, CRCST, NREMT, CHL
Jill Holdsworth, MS, CIC, FAPIC, CRCSR, NREMT, CHL, and Katie Belski, BSHCA, CRCST, CHL, CIS
Baby visiting a pediatric facility  (Adobe Stock 448959249 by
Antimicrobial Resistance (Adobe Stock unknown)
Anne Meneghetti, MD, speaking with Infection Control Today
Patient Safety: Infection Control Today's Trending Topic for March
Infection Control Today® (ICT®) talks with John Kimsey, vice president of processing optimization and customer success for Steris.
Picture at AORN’s International Surgical Conference & Expo 2024
Infection Control Today and Contagion are collaborating for Rare Disease Month.
Related Content