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2018-2019 Influenza Season Week 18 ending May 4, 2019
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  • Description:
    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 continues to decrease in the United States. While influenza A(H1N1)pdm09 viruses predominated from October to mid-February, influenza A(H3N2) viruses have been more commonly identified since late February. Small numbers of influenza B viruses also have been reported. Below is a summary of the key influenza indicators for the week ending May 4, 2019: • Viral Surveillance: The percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories decreased. During the most recent three weeks, influenza A(H3) viruses were reported more frequently than influenza A(H1N1)pdm09 viruses nationally. • Virus Characterization: The majority of influenza A(H1N1)pdm09 and influenza B viruses characterized antigenically are similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses. However, the majority 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. • Antiviral Resistance: The vast majority of influenza viruses tested (>99%) show susceptibility to oseltamivir and peramivir. All influenza viruses tested showed susceptibility to zanamivir. • Influenza-like Illness Surveillance:The proportion of outpatient visits for influenza-like illness (ILI) decreased to 1.6%, which is below the national baseline of 2.2%. One region reported ILI at their region-specific baseline level. • ILI State Activity Indictor Map: Two states experienced low ILI activity; and New York City, the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 48 states experienced minimal ILI activity. • Geographic Spread of Influenza: The geographic spread of influenza in two states was reported as widespread; Puerto Rico and seven states reported regional activity; 18 states reported local activity; the District of Columbia, the U.S. Virgin Islands and 22 states reported sporadic activity; one state reported no activity; and Guam did not report. • Influenza-associated Hospitalizations A cumulative rate of 65.7 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. The highest hospitalization rate is among adults 65 years and older (221.5 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. • Influenza-associated Pediatric Deaths: Five influenza-associated pediatric deaths were reported to CDC during week 18.
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