Influenza Hospitalization Surveillance Network (FluSurv-NET)
Population-based surveillance is the collection, analysis and interpretation of data on a population in a specified area.
FluSurv-NET is a population-based surveillance system.
About FluSurv-NET
The Influenza Hospitalization Surveillance Network (FluSurv-NET) is a population-based surveillance system that collects data on laboratory-confirmed influenza-associated hospitalizations among children and adults through a network of acute care hospitals in 14 states.
Why FluSurv-NET Data is Important
FluSurv-NET is CDC’s source for important data on hospitalization rates associated with flu. FluSurv-NET also provides demographic and clinical information including age, sex and underlying medical conditions among persons hospitalized with flu. Data gathered are used to estimate age-specific hospitalization rates on a weekly basis and to describe characteristics of persons hospitalized with influenza illness.
FluSurv-NET Data Collection
For FluSurv-NET, a case is defined as a person who is a resident in a defined FluSurv-NET catchment area and tests positive for influenza by a laboratory test ordered by a health care professional within 14 days prior to or during hospitalization. Laboratory confirmation is defined by a positive result of a viral culture, direct or indirect fluorescent antibody staining, rapid antigen test, or molecular assay.
Clinical data are abstracted from medical charts by trained surveillance officers using a standardized case report form, so the data are collected in a uniform way. The following types of data are collected for each case:
- age
- sex
- race and ethnicity
- surveillance site
- current season influenza vaccination status
- date of hospital admission
- evidence of positive influenza test
- clinical (medical) history (underlying health conditions)
- clinical course
- medical interventions (e.g., receipt of antiviral treatment, mechanical ventilation)
- outcomes (e.g., discharged from the hospital, in-hospital death)
How FluSurv-NET Calculates Hospitalization Rates
Hospitalization rates are calculated as the number of residents of a defined area who are hospitalized with a positive influenza laboratory test divided by the total population within the defined area. NCHS bridged-race population estimates are used as denominators.
FluSurv-NET Coverage
FluSurv-NET coverage area includes more than 70 counties in 14 states that participate in the Emerging Infections Program (EIP) and the Influenza Hospitalization Surveillance Program (IHSP). Participating states include: California, Colorado, Connecticut, Georgia, Iowa, Maryland, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee and Utah.
FluSurv-NET covers more than 29 million people and includes an estimated 9 percent of the U.S. population. The counties covered are located in all 10 Health and Human Services (HHS) regionsexternal icon. The designated FluSurv-NET surveillance area is generally similar to the U.S. population by demographics; however, the information might not be generalizable to the entire country.
Accessing FluSurv-NET Data
Influenza-associated hospitalization rates are reported to CDC on a weekly basis from October 1 through April 30 of each influenza season. FluSurv-NET data, including hospitalization rates for different age groups and data on patient characteristics, are available on Fluview and Fluview Interactive.
FluSurv-NET hospitalization data are preliminary during each season; data presented may change as more reports are received. In particular, case counts for recent hospital admissions are subject to reporting lags. As data are received each week during the influenza season, prior case counts and rates may be updated.
How FluSurv-NET contributes to CDC’s Influenza Burden Estimates
CDC uses FluSurv-NET data in combination with other data sources to estimate annual and weekly disease burden of influenza in the United States. Estimates are made of symptomatic illnesses, medically attended illnesses, hospitalizations and deaths. Reported rates are adjusted in an attempt to correct for the under-detection of influenza. This adjustment is done by using the percent of people hospitalized with respiratory illnesses who were tested for influenza and the average sensitivity of influenza tests used in the participating FluSurv-NET hospitals. Weekly estimates of influenza burden are available during each influenza season. Annual estimates of US influenza burden flu burden averted by influenza vaccination are available online.
FluSurv-NET Publications
- Study: Acute Cardiovascular Events Associated with Influenza in Hospitalized Adults: A Cross-sectional Studyexternal icon. Annals of Internal Medicine. 2020
- Study: Respiratory and Nonrespiratory Diagnoses Associated with Influenza in Hospitalized Adultsexternal icon. JAMA Network Open. 2020.
- Study: Outcomes of Immunocompromised Adults Hospitalized with Laboratory-confirmed Influenza in the United States, 2011-2015external icon. Clinical Infectious Diseases. 2019
- Study: Clinical Features and Outcomes of Immunocompromised Children Hospitalized with Laboratory-Confirmed Influenza in the United States, 2011-2015external icon. Journal of the Pediatric Infectious Diseases Society. 2018
- Study: Age-Related Differences in Hospitalization Rates, Clinical Presentation, and Outcomes Among Older Adults Hospitalized with Influenza – U.S. Influenza Hospitalization Surveillance Network (FluSurv-NET)external icon. Open Forum Infectious Diseases. 2019
- Study: Projected Population Benefit of Increased Effectiveness and Coverage of Influenza Vaccination on Influenza Burden in the United States.external icon Clinical Infectious Diseases. 2019
- Study: Effects of Influenza Vaccination in the United States During the 2017–2018 Influenza Seasonexternal icon. Clinical Infectious Diseases. 2019
- Study: Birth Cohort Effects in Influenza Surveillance Data: Evidence that First Influenza Infections Affects later Influenza-Associated Illnessexternal icon. The Journal of Infectious Diseases. 2019
- Study: Influenza-Related Hospitalizations and Poverty Levels — United States, 2010–2012.pdf icon Morbidity and Mortality Weekly Report (MMWR). 2016
- Study: Increased Antiviral Treatment Among Hospitalized Children and Adults With Laboratory-Confirmed Influenza, 2010–2015.external icon Clinical Infectious Diseases. 2016
- Study: Influenza Vaccination Modifies Disease Severity Among Community-dwelling Adults Hospitalized with Influenzaexternal icon. Clinical Infectious Diseases. 2017
- Study: Improving Accuracy of Influenza-Associated Hospitalization Rate Estimates.pdf iconexternal icon Emerging Infectious Diseases. 2015
- The US Influenza Hospitalization Surveillance Networkexternal icon. Emerging Infectious Diseases. 2015