U.S. Virologic Surveillance

Clinical Laboratories

The results of tests performed by clinical laboratories nationwide are summarized below. Data from clinical laboratories (the percentage of specimens tested that are positive for influenza) are used to monitor whether influenza activity is increasing or decreasing.

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Public Health Laboratories

The results of tests performed by public health laboratories nationwide are summarized below. Data from public health laboratories are used to monitor the proportion of circulating viruses that belong to each influenza subtype/lineage.

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Additional virologic surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or Age Data

Outpatient Illness Surveillance

ILINet

Nationwide during week 15, 2.9% of patient visits reported through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) were due to influenza-like illness (ILI). This percentage is above the national baseline of 2.4%.

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On a regional level, the percentage of outpatient visits for ILI ranged from 1.3% to 8.3% during week 15. The percent of outpatient visits for ILI decreased in all regions compared to last week. Regions 1, 2, 3, 5, and 10 reported a percentage of outpatient visits for ILI at or above their region-specific baselines. All other regions are below their region-specific baselines.

ILI Activity Map

Data collected in ILINet are used to produce a measure of ILI activity* by state.

During week 15, the following ILI activity levels were experienced:

• Very High – New York City and 1 state (New Jersey)
• High – the District of Columbia, Puerto Rico, and 8 states (Connecticut, Georgia, Louisiana, Maryland, Massachusetts, New York, South Carolina, and Wisconsin)
• Moderate – six states (Illinois, Oklahoma, Oregon, Pennsylvania, Vermont, and Virginia)
• Low - 11 states (Alabama, Alaska, Colorado, Idaho, Kansas, Minnesota, Nebraska, New Mexico, Tennessee, Texas, and Washington)
• Minimal - 24 states (Arizona, Arkansas, California, Delaware, Florida, Hawaii, Indiana, Iowa, Kentucky, Maine, Michigan, Mississippi, Missouri, Montana, Nevada, New Hampshire, North Carolina, North Dakota, Ohio, Rhode Island, South Dakota, Utah, West Virginia, and Wyoming)
• Data were insufficient to calculate an ILI activity level from the U.S. Virgin Islands.

*Data collected in ILINet may disproportionally represent certain populations within a state, and therefore, may not accurately depict the full picture of influenza activity for the whole state. Differences in the data presented here by CDC and independently by some state health departments likely represent differing levels of data completeness with data presented by the state likely being the more complete.

Additional information about medically attended visits for ILI for current and past seasons:
Surveillance Methods | FluView Interactive: National, Regional, and State Data or ILI Activity Map

Geographic Spread of Influenza as Assessed by State and Territorial Epidemiologists

The influenza activity reported by state and territorial epidemiologists indicates geographic spread of influenza viruses but does not measure the severity of influenza activity.

During week 15, the following influenza activity was reported:

• Widespread – 3 states (Indiana, Louisiana, and Maryland)
• Regional – Puerto Rico and 13 states (Arizona, Georgia, Idaho, Maine, Nevada, New Hampshire, New Jersey, North Carolina, Ohio, Oklahoma, South Carolina, Tennessee and Wisconsin)
• Local – the District of Columbia and 11 states (Colorado, Illinois, Kansas, Massachusetts, Michigan, Montana, Oregon, Pennsylvania, Texas, Washington and Wyoming)
• Sporadic – the U.S. Virgin Islands and 19 states (Alabama, Alaska, Arkansas, California, Connecticut, Florida, Hawaii, Iowa, Kentucky, Minnesota, Mississippi, Missouri, Nebraska, New York, North Dakota, South Dakota, Utah, Vermont and West Virginia)
• No Activity – four states (Delaware, New Mexico, Rhode Island and Virginia)
• Guam did not report.

Additional geographic spread surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Influenza-Associated Hospitalizations

The Influenza Hospitalization Surveillance Network (FluSurv-NET) conducts population-based surveillance for laboratory-confirmed influenza-related hospitalizations in select counties in the Emerging Infections Program (EIP) states and Influenza Hospitalization Surveillance Project (IHSP) states.

A total of 19,845 laboratory-confirmed influenza-associated hospitalizations were reported by FluSurv-NET sites between October 1, 2019 and April 11, 2020 with a cumulative hospitalization rate of 68.3 per 100,000 population.

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Additional hospitalization surveillance information for current and past seasons and additional age groups:
Surveillance Methods | FluView Interactive: Rates by Age or Patient Characteristics

Pneumonia and Influenza (P&I) Mortality Surveillance

Based on National Center for Health Statistics (NCHS) mortality surveillance data available on April 16, 2020, 11.9% of the deaths occurring during the week ending April 11, 2020 (week 15) were due to P&I. This percentage is above the epidemic threshold of 7.0% for week 15.

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Additional pneumonia and influenza mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Influenza-Associated Pediatric Mortality

Two influenza-associated pediatric deaths occurring during the 2019-2020 season were reported to CDC during week 15. One death was associated with an influenza A (H1N1)pdm09 virus and occurred during week 52 (the week ending December 28, 2019). One death was associated with an influenza B/Victoria virus and occurred during week 2 (the week ending January 11, 2020).

A total of 168 influenza-associated pediatric deaths occurring during the 2019-2020 season have been reported to CDC.

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Additional pediatric mortality surveillance information for current and past seasons:
Surveillance Methods | FluView Interactive

Additional National and International Influenza Surveillance Information

FluView Interactive: FluView includes enhanced web-based interactive applications that can provide dynamic visuals of the influenza data collected and analyzed by CDC. These FluView Interactive applications allow people to create customized, visual interpretations of influenza data, as well as make comparisons across flu seasons, regions, age groups and a variety of other demographics. To access these tools, visit http://www.cdc.gov/flu/weekly/fluviewinteractive.htm

National Institute for Occupational Safety and Health: Monthly surveillance data on the prevalence of health-related workplace absenteeism among full-time workers in the United States are available from NIOSH at https://www.cdc.gov/niosh/topics/absences/default.html

U.S. State and local influenza surveillance:Select a jurisdiction below to access the latest local influenza information

Alabama	Alaska	Arizona	Arkansas	California
Colorado	Connecticut	Delaware	District of Columbia	Florida
Georgia	Hawaii	Idaho	Illinois	Indiana
Iowa	Kansas	Kentucky	Louisiana	Maine
Maryland	Massachusetts	Michigan	Minnesota	Mississippi
Missouri	Montana	Nebraska	Nevada	New Hampshire
New Jersey	New Mexico	New York	North Carolina	North Dakota
Ohio	Oklahoma	Oregon	Pennsylvania	Rhode Island
South Carolina	South Dakota	Tennessee	Texas	Utah
Vermont	Virginia	Washington	West Virginia	Wisconsin
Wyoming	New York City	Puerto Rico	Virgin Islands

World Health Organization: Additional influenza surveillance information from participating WHO member nations is available through FluNet and the Global Epidemiology Reports.

WHO Collaborating Centers for Influenza located in Australia, China, Japan, the United Kingdom, and the United States (CDC in Atlanta, Georgia).

Europe: For the most recent influenza surveillance information from Europe, please see WHO/Europe and the European Centre for Disease Prevention and Control at http://www.flunewseurope.org/.

Public Health Agency of Canada: The most up-to-date influenza information from Canada is available at http://www.phac-aspc.gc.ca/fluwatch/

Public Health England: The most up-to-date influenza information from the United Kingdom is available at https://www.gov.uk/government/statistics/weekly-national-flu-reports

Any links provided to non-Federal organizations are provided solely as a service to our users. These links do not constitute an endorsement of these organizations or their programs by CDC or the Federal Government, and none should be inferred. CDC is not responsible for the content of the individual organization web pages found at these links.

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.

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