COVID-NET Overview and Methods

About COVID-NET

The Coronavirus Disease 2019 (COVID-19) Hospitalization Surveillance Network (COVID-NET) is part of the Respiratory Virus Hospitalization Surveillance Network (RESP-NET) which is designed to conduct population-based surveillance for laboratory-confirmed COVID-19, RSV, and influenza-associated hospitalizations. RESP-NET also includes surveillance networks for respiratory syncytial virus (RSV) and influenza (also known as RSV-NET and FluSurv-NET, respectively).

COVID-NET collects surveillance data on laboratory-confirmed, COVID-19-associated hospitalizations among children and adults. Data are collected and reported from a network of sites in acute-care hospitals across 98 counties in 13 states.

Why COVID-NET Data Are Important

Tracking COVID-19-associated hospitalization rates helps public health professionals understand trends in virus circulation, estimate disease burden, and respond to outbreaks. Hospitalization rates are updated weekly on the COVID-NET Interactive Data Dashboard. Collecting demographic and more detailed clinical information, including underlying conditions, allows CDC to better understand COVID-19-associated hospitalization trends and determine who is most at risk.

Hospitalization rates show how many people in the surveillance area are hospitalized with COVID-19, compared to the total number of people residing in that area.

Case Definition

A case is defined by laboratory confirmed SARS-CoV-2 in a person who:

• Lives in a defined COVID-NET surveillance area AND
• Tests positive for SARS-CoV-2 within 14 days before or during hospitalization.

Evidence of COVID-19 infection can be obtained through several laboratory tests:

• Molecular assays, such as reverse transcription polymerase chain reaction (RT-PCR)
• Commercially available rapid antigen detection tests
• Serology (antibody) tests (must be paired acute and convalescent specimens)

Calculating Hospitalization Rates

To calculate COVID-19-associated hospitalization rates, COVID-NET collects the following data from identified cases:

• Age
• Sex
• Race and ethnicity
• County of residence
• Date of hospital admission
• Date of SARS-CoV-2 test
• Positive SARS-CoV-2 test result

Hospitalization rates are calculated as the number of residents in a surveillance area who are hospitalized with laboratory-confirmed COVID-19, divided by the total population estimate for that area. NCHS bridged-race population estimates are used as denominators for rate calculations.

How COVID-NET Hospitalization Data Are Different from Hospitalizations Reported in National and State Case Counts

COVID-NET data differ from hospitalizations reported in national and state case counts in multiple ways. First, state and national COVID-19 case reporting is based on all people who test positive using a healthcare provider-administered test for COVID-19 in the United States. COVID-NET is limited to COVID-19-associated hospitalizations captured in the COVID-NET surveillance area. Second, COVID-NET reports rates, not just counts. These rates show how many people are hospitalized with COVID-19 in the surveillance area, compared to the population residing in that area.

Collecting Clinical Data

COVID-NET surveillance began tracking COVID-19-associated hospitalizations in adults in March of 2020.

Cases are identified by reviewing state surveillance system databases, health information exchanges, hospital admission and laboratory databases, and infection control logs for patients hospitalized with a positive SARS-CoV-2 test result. Data collected are used to estimate age-specific hospitalization rates on a weekly and monthly basis and describe demographic and clinical characteristics of patients hospitalized with COVID-19.

Trained surveillance officers collect clinical data using a standardized case reporting form. Clinical data collected include:

• Medical history (e.g., underlying health conditions)
• Clinical course (i.e., progression of the COVID-19 illness such as admission to an ICU)
• Medical interventions (i.e., medical care for the COVID-19 illness such as need for mechanical ventilation)
• Outcomes (i.e., discharged from the hospital, or death)
• COVID-19 vaccination history

COVID-NET Surveillance Area

COVID-NET currently comprises 98 counties in the 13 states participating in the Emerging Infections Program (EIP) and the Influenza Hospitalization Surveillance Project (IHSP). The participating states are California, Colorado, Connecticut, Georgia, Maryland, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee, and Utah.

COVID-NET covers approximately 10 percent of the U.S. population. The counties covered are located in 9 of the 10 Health and Human Services (HHS) regions. The designated COVID-NET surveillance area is generally similar to the U.S. population by demographics; however, the statistics generated using COVID-NET data might not be generalizable to the entire country.

The map and table, above, describe the current sites participating in COVID-NET. The table below summaries changes in participating sites by surveillance season. Data used to calculate hospitalization rates are generated by all counties included in surveillance. Clinical data on medical history, clinical course, medical interventions, outcomes, and vaccination history are reported using data from a subset of these counties.

COVID-NET Publications