RSV-NET Overview and Methods

About RSV-NET

The Respiratory Syncytial Virus Hospitalization Surveillance Network (RSV-NET) is part of 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 COVID-19 and influenza (also known as COVID-NET and FluSurv-NET, respectively).

RSV-NET collects surveillance data on laboratory-confirmed, RSV-associated hospitalizations, including those resulting in ICU admission or death, among children and adults. Data are collected and reported from a network of sites in acute-care hospitals across 58 counties in 12 states during the October 1–April 30 season each year. In some years, additional months of data are collected.

RSV-NET Interactive Dashboard

See the rates of RSV-associated hospitalizations each year

For the different RSV-NET surveillance years: Clinical Data Table

More details: RSV-NET Publications

Why RSV-NET Data are Important

RSV-NET is a population-based surveillance system. Population-based surveillance is the active collection, analysis, and interpretation of data on a population in a specified geographic area.

RSV can cause serious disease that results in thousands of hospitalizations each year in the United States.

Tracking RSV-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 RSV-NET Interactive Dashboard. Collecting demographic and more detailed clinical information, including underlying conditions, allows CDC to better understand RSV-associated hospitalization trends and determine who is most at risk.

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

Case Definition

A case is defined by laboratory-confirmed RSV in a person who:

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

Evidence of RSV 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 tests, or antibody tests (must be paired acute and convalescent specimens)
  • Immunofluorescence antibody staining, including direct (DFA) and indirect (IFA) fluorescent antibody tests
  • Viral culture

Calculating Hospitalization Rates

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

  • Age
  • Sex
  • Race and ethnicity
  • County of residence
  • Date of hospital admission
  • Date of RSV test
  • Positive RSV test result

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

RSV-NET conducts surveillance for laboratory-confirmed, RSV-associated hospitalizations across a network of acute-care hospital facilities in 12 states covering almost 8% of the U.S. population. RSV-NET does not identify every RSV-associated hospitalization at these facilities:

  • Patients hospitalized with RSV who are not tested for RSV would not be identified in RSV-NET, which relies on laboratory confirmation.
  • Patients may seek medical care later in their illness when RSV infection can no longer be detected and laboratory test results are negative.
  • State health departments are not required to report RSV-associated hospitalizations to CDC.

Collecting Clinical Data

RSV-NET surveillance began tracking RSV-associated hospitalizations in adults in the 2016–2017 season and in children in the 2018–2019 season.

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 RSV 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 RSV.

Trained RSV-NET 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 RSV illness such as admission to an ICU)
  • Medical interventions (i.e., medical care for the RSV illness such as need for mechanical ventilation)
  • Outcomes (i.e., discharged from the hospital, or death)

The table below summarizes changes in surveillance populations and collection of clinical data by surveillance year. Because the surveillance areas and age groups included in surveillance have changed over time, trends should be interpreted with caution (see table below).

Summary of changes in surveillance populations and collection of clinical data by surveillance year
Year of Surveillance Surveillance Population Cases with Clinical Data Collected
2014–2015 Adults in GA, MD, MN, NY, OR, TN All adults (excluding Oregon)
2015–2016 Adults in CA, GA, MD, MN, NY, OR, TN All adults (excluding Oregon)
2016–2017 Adults in CA, GA, MD, MN, NY, OR, TN All adults
2017–2018 Adults in CA, GA, MD, MN, NM, NY, OR, TN All adults
2018–2019 Children and adults in all participating states Children and adults admitted to an intensive care unit (ICU) or who died in hospital or within 60 days of hospital discharge
2019–2020 Children and adults in all participating states Limited data collection due to COVID-19 pandemic
2020–2021 Children and adults in all participating states Children and adults admitted to the ICU or who died in hospital or within 60 days of hospital discharge
2021–2022 Children and adults in all participating states Children and adults admitted to the ICU or who died in hospital or within 60 days of hospital discharge and pregnant women

Participating States

RSV-NET currently comprises 58 counties in 12 states that participate in the Emerging Infections Program (EIP) or the Influenza Hospitalization Surveillance Program (IHSP). The 12 participating states are California, Colorado, Connecticut, Georgia, Maryland, Michigan, Minnesota, New Mexico, New York, Oregon, Tennessee, and Utah.

RSV-NET covers almost 8% of the U.S. population. The RSV-NET surveillance area is generally similar to the U.S. population by demographics; however, RSV-NET data might not be generalizable to the entire country.