Surveillance of RSV

Surveillance and research systems

CDC has several systems that focus on monitoring and describing seasonal trends, clinical risk factors, rates of illness and hospitalization, and demographics of patients seeking care for illness associated with respiratory syncytial virus (RSV).

• The National Respiratory and Enteric Virus Surveillance System (NREVSS) is a laboratory-based system that monitors seasons and circulation patterns of RSV and other viruses.
• The National Syndromic Surveillance Program (NSSP) is a collaboration among CDC, federal partners, state and local health departments, and academic and private sector partners to collect, analyze, and share electronic data received from emergency departments and other health care settings.
• The RSV Hospitalization Surveillance Network (RSV-NET) is an active population-based surveillance system for RSV-associated hospitalizations in the U.S. among children and adults.
• The New Vaccine Surveillance Network (NVSN) is a multisite, active, population-based pediatric surveillance network for acute respiratory hospitalizations and outpatient visits associated with RSV and other respiratory pathogens.
• The Investigating Respiratory Viruses in the Acutely Ill (IVY) Network is a multisite, active surveillance network designed to assess how well vaccines work to prevent COVID-19, flu, and RSV-associated hospitalizations among adults. (Note: the IVY Network is not conducting surveillance during the 2025-2026 RSV season.)
• The RSV Surveillance in Native American Children and Adults (RSV SuNA) collaboration monitors for RSV-associated hospitalizations and outpatient visits among Alaska Native and American Indian persons and is conducted on the Navajo Nation, White Mountain Apache Tribal Lands, and in Alaska. Additional information about other research and surveillance activities among Alaska Native persons may be provided by the Arctic Investigations Program.

Learn more about RSV burden estimates

• Preliminary Estimates of RSV Burden

• How CDC Estimates RSV Burden in the U.S.

RSV seasonal trends

How are data collected?

CDC collects RSV laboratory test results performed in the United States using the National Respiratory and Enteric Virus Surveillance System (NREVSS). CDC presents data on RSV activity at the national, regional, and state levels. NREVSS is a voluntary, laboratory-based surveillance system established in the 1980s to monitor seasonal trends of several viruses, including RSV. Through NREVSS, participating laboratories report the total number of weekly RSV tests by diagnostic method and the number of those tests that were positive. Data from NREVSS provides information to public health officials and healthcare providers about the presence of RSV in their communities.

What are the typical seasonal patterns?

In most regions of the United States and other areas with similar climates, the RSV season typically starts during the fall and peaks in the winter. RSV circulation was disrupted by the COVID-19 pandemic, but recent RSV data from NREVSS suggests a return to pre-pandemic RSV circulation.

RSV season onset, peak, and offset are identified using the 3% positivity threshold. This method has been used prospectively and captured a high proportion of RSV positive tests during the pre-pandemic RSV seasons.

• RSV season onset is defined as the first of two consecutive weeks when the weekly percentage of positive RSV PCR tests reaches or exceeds 3% (ranged from mid-September to November).
• RSV season peak is defined as the week with the highest percentage of the weekly PCR tests positive for RSV (ranged from November to February).
• RSV season offset (pre-pandemic) is defined as the last of two consecutive weeks when the percentage of RSV PCR tests reach or exceeds 3% (ranged from early-February to May).

These seasonal patterns are based on NREVSS data from before the COVID-19 pandemic (2017-2020), in all 10 U.S. Department of Health and Human Services (HHS) regions (except Alaska, Florida and Hawaii). Florida has an earlier RSV season onset and longer duration than most regions of the country.