Influenza activity continues to increase in the United States. Influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B viruses continue to co-circulate. Below is a summary of the key influenza indicators for the week ending Feb. 16, 2019:
Influenza-like Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) increased to 5.1%, which is above the national baseline of 2.2%. All 10 regions reported ILI at or above their region-specific baseline level.
ILI State Activity Indicator Map: New York City and 30 states experienced high ILI activity; the District of Columbia and 11 states experienced moderate ILI activity; six states experienced low ILI activity; the U.S. Virgin Islands and three states experienced minimal ILI activity; and Puerto Rico had insufficient data.
Geographic Spread of Influenza: The geographic spread of influenza in 48 states was reported as widespread; one state reported regional activity; the District of Columbia reported local activity; the U.S. Virgin Islands and one state reported sporadic activity; and Guam did not report.
Influenza-associated HospitalizationsA cumulative rate of 27.4 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. The highest hospitalization rate is among adults 65 years and older (75.6 hospitalizations per 100,000 population).
Pneumonia and Influenza Mortality:The proportion of deaths attributed to pneumonia and influenza (P&I) was below the system-specific epidemic threshold in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
Viral Surveillance: The percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories increased. While influenza A(H1N1)pdm09 viruses predominated in most areas of the country, influenza A(H3) viruses have predominated in HHS Region 4 and accounted for 47% of sub-typed influenza A viruses detected nationally during week 7. During the most recent three weeks, influenza A(H3) viruses were reported more frequently than influenza A(H1N1)pdm09 viruses in HHS Regions 6 and 7 and influenza A(H1N1)pdm09 and influenza A(H3) viruses were reported in approximately equal numbers in HHS Region 2.
Virus Characterization: The majority of influenza viruses characterized antigenically are similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses.
Antiviral Resistance: The vast majority of influenza viruses tested (>99%) show susceptibility to oseltamivir and peramivir. All influenza viruses tested showed susceptibility to zanamivir.