Weekly U.S. Influenza Surveillance Report

CDC's Influenza Division produces a weekly influenza surveillance report, FluView. According to this week's report (Sept 30 - Oct 6), seasonal influenza activity is at levels below baseline in the United States.

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2018-2019 Influenza Season Week 40 ending October 6, 2018

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.,

Background:

The Centers for Disease Control and Prevention’s (CDC) Influenza Division collects, compiles, and analyzes information on influenza activity year-round in the United States and produces FluView, a weekly influenza surveillance report, and FluView Interactive , an application to customize the presentation of influenza surveillance data. The U.S. influenza surveillance system provides information in five categories collected from eight data sources. This is the first report of the 2018-19 influenza season.

The five categories and eight data components of CDC influenza surveillance are:

Viral Surveillance: U.S. World Health Organization (WHO) collaborating laboratories, the National Respiratory and Enteric Virus Surveillance System (NREVSS), and human infection with novel influenza A virus case reporting;
Outpatient Illness Surveillance: U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet);
Geographic Spread of Influenza: State and territorial epidemiologists’ reports;
Hospitalizations: Influenza Hospitalization Network (FluSurv-NET) including the Emerging Infections Program (EIP) and three additional states;
Mortality: National Center for Health Statistics (NCHS) Mortality Surveillance System and influenza-associated pediatric deaths.

Synopsis:

Influenza activity in the United States remained low throughout the summer months and early October.

Viral Surveillance: While influenza B viruses were more commonly detected from May until late June, influenza A viruses have predominated from the beginning of July onward. The percentage of respiratory specimens testing positive for influenza in clinical laboratories is low.

Virus Characterization: The majority of tested influenza viruses were characterized antigenically and genetically as being similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses.
Antiviral Resistance: All tested viruses showed susceptibility to antiviral drugs.

Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) remained low and was 1.4%, which is below the national baseline of 2.2%. All 10 regions reported ILI below region-specific baseline levels.

ILI State Activity Indictor Map: New York City, the District of Columbia, and 49 states experienced minimal ILI activity, and Puerto Rico and one state had insufficient data.

Geographic Spread of Influenza: The geographic spread of influenza in two states was reported as local activity; the District of Columbia, the U.S. Virgin Islands and 35 states reported sporadic activity; 12 states reported no activity; and Guam, Puerto Rico and one state did not report.
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: Two influenza-associated pediatric deaths were reported that occurred during the 2017-2018 season. No influenza-associated pediatric deaths for the 2018-2019 season have been reported to CDC.