2018-2019 Influenza Season Week 12 ending March 23, 2019

All data are preliminary and may change as more reports are received.An overview of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available at http://www.cdc.gov/flu/weekly/overview.htm.Synopsis: Influenza activity decreased but remains elevated in the United States. Influenza A(H1N1)pdm09 viruses predominated from October to mid-February and influenza A(H3N2) viruses have been more commonly identified since late February. Small numbers of influenza B viruses have also been reported. Below is a summary of the key influenza indicators for the week ending March 23, 2019\u2022 Viral Surveillance: The percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories decreased. Nationally, during the most recent three weeks, influenza A(H3) viruses were reported more frequently than influenza A(H1N1)pdm09 viruses and in all 10 HHS Regions.o Virus Characterization: The majority of influenza viruses characterized antigenically are similar to the cell-grown reference viruses representing the 2018\u20132019 Northern Hemisphere influenza vaccine viruses. However, an increasing proportion of influenza A(H3N2) viruses are antigenically distinguishable from A/Singapore/INFIMH-16-0019/2016 (3C.2a1), a cell-propagated reference virus representing the A(H3N2) component of 2018-19 Northern Hemisphere influenza vaccines.o Antiviral Resistance:The vast majority of influenza viruses tested (>99%) show susceptibility to oseltamivir and peramivir. All influenza viruses tested showed susceptibility to zanamivir.\u2022 Influenza-like Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) decreased to 3.8%, and remains above the national baseline of 2.2%. All 10 regions reported ILI at or above their region-specific baseline level.o ILI State Activity Indictor Map: 20 states experienced high ILI activity; Puerto Rico and 13 states experienced moderate ILI activity; New York City, the District of Columbia and seven states experienced low ILI activity; 10 states experienced minimal ILI activity; and the U.S. Virgin Islands had insufficient data.\u2022 Geographic Spread of Influenza: The geographic spread of influenza in Puerto Rico and 34 states was reported as widespread; 14 states reported regional activity; the District of Columbia and two states reported local activity; the U.S. Virgin Islands reported sporadic activity; and Guam did not report.\u2022 Influenza-associated Hospitalizations A cumulative rate of 52.5 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. The highest hospitalization rate is among adults 65 years and older (167.0 hospitalizations per 100,000 population).\u2022 Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was above the system-specific epidemic threshold in the National Center for Health Statistics (NCHS) Mortality Surveillance System.\u2022 Influenza-associated Pediatric Deaths: One influenza-associated pediatric death was reported to CDC during week 12.2019713