Weekly U.S. Influenza Surveillance Report

CDC's Influenza Division produces a weekly influenza surveillance report, FluView. According to this week's report (Apr 7-13), seasonal flu activity decreased in the United States, but remains elevated. Eleven states are reporting widespread flu activity. CDC estimates that flu has caused as many as 41.3 million flu illnesses, 610,000 hospitalizations and 57,300 deaths so far this season.

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Synopsis:

Influenza activity continues to decrease in the United States, but remains elevated. 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 also have been reported. Below is a summary of the key influenza indicators for the week ending April 13, 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, and in all 10 HHS Regions.

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 2.4%, but remains above the national baseline of 2.2%. Seven of 10 regions reported ILI at or above their region-specific baseline level.

ILI State Activity Indictor Map: One state experienced high ILI activity; five states experienced moderate ILI activity; New York City, Puerto Rico and 14 states experienced low ILI activity; the District of Columbia and 30 states experienced minimal ILI activity; and the U.S. Virgin Islands had insufficient data.

Geographic Spread of Influenza: The geographic spread of influenza in 11 states was reported as widespread; Puerto Rico and 20 states reported regional activity; the District of Columbia and 17 states reported local activity; the U.S. Virgin Islands and two states reported sporadic activity; Guam did not report.
Influenza-associated Hospitalizations A cumulative rate of 62.3 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. The highest hospitalization rate is among adults 65 years and older (206.5 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 15.