Release Notes & Frequently Asked Questions

Overall respiratory illness activity

Summary:

• Indicates whether the amount of people going to the emergency department for respiratory illness is minimal, low, moderate, high, or very high.

Explanation:

• Respiratory illness activity is monitored using the acute respiratory illness (ARI) definition. ARI captures a broad range of emergency department visits for respiratory illnesses, ranging from the common cold to potentially severe illnesses like flu (influenza), RSV and COVID-19. It captures a broader range of respiratory illnesses, including those that do not present with fever, compared to the previously shown influenza-like illness (ILI) metric (Note: the ILI metric is still being used for flu monitoring).
• Respiratory illness activity levels are based on comparing the percent of emergency department visits for ARI during the current week to the average percent of visits during times when COVID-19, flu and RSV visits were low (Note: other respiratory illness-related visits may still be occurring). These low points are considered "baseline" levels of respiratory illness activity The activity level is based on how elevated the current week is from the "baseline" period. See Activity Levels data notes for the detailed methodology.
• Emergency department data are collected through the National Syndromic Surveillance Program.

Wastewater viral activity level

Summary:

• Indicates whether the amount of virus in the wastewater for specific respiratory illnesses is minimal, low, moderate, high, or very high.

Explanation:

• Wastewater data are collected through the National Wastewater Surveillance System (NWSS). Wastewater monitoring can detect viruses spreading in a community whether or not people have symptoms. It does not depend on people having access to healthcare or visiting a doctor for testing. Increased wastewater viral activity levels may indicate increased risk of infection in an area.
• Wastewater data may show changes in disease trends earlier than data from clinical cases. For example, wastewater data can be used as an early indicator for monitoring the spread of infection before people have symptoms or require medical care. Therefore, wastewater levels may go up (or down) before we see changes in metrics like emergency department use. Wastewater surveillance can complement other existing surveillance systems to monitor respiratory viruses.
  
• Wastewater testing for influenza cannot determine the source of the influenza viruses detected. The viruses could come from a human or from an animal (like a bird) or an animal product (like milk from an infected cow); therefore, these detections do not necessarily indicate human cases.
• Wastewater testing for influenza displayed in these visuals only detects influenza A viruses and does not distinguish between influenza A subtypes e.g. seasonal influenza A(H1N1), seasonal influenza A(H3N2) and avian influenza A(H5).
• Wastewater data will not include waste that may be disposed of outside the wastewater system, such as from people wearing diapers. This likely explains why trends in wastewater data for RSV do not always align with emergency department visits for RSV, which causes severe disease primarily in infants under 6 months and older adults.
• States or territories with limited coverage are those where wastewater monitoring covers a small segment (less than 5%) of the state or territory population. Because data from limited coverage areas may not fully reflect infections for the larger population, wastewater viral activity levels are not shown on the 'Your community snapshot'. Levels are shown in limited coverage areas with hatch marks on the activity level page. These data are also made available on the National Wastewater Surveillance System homepage.
• Wastewater monitoring data are not available in all communities or in areas that are not connected to a wastewater treatment system.
• The wastewater viral activity level (WVAL) is available for the virus that causes COVID-19 (SARS-COV-2), Influenza A, and RSV present in samples of wastewater taken from sites across the United States. More detailed methods can be found in About Wastewater Data | National Wastewater Surveillance System | CDC.

Emergency department visits

Summary:

• Indicates whether the amount of people going to the emergency department for COVID-19, flu or RSV is minimal, low, moderate, high, or very high.

Explanation:

• Emergency department data are collected through the National Syndromic Surveillance Program.
• Activity levels are based on comparing the percent of emergency department visits for COVID-19, flu, or RSV visits during the current week to the average percent of visits when COVID-19, flu, or RSV visits were low, respectively.
• These low points represent what are considered “baseline” levels. The activity level is based on how elevated the current week is from the “baseline” period. See Activity Levels data notes for the detailed methodology.

Emergency department visit trends

Summary:

• Describes changes in the percentage of emergency department visits for COVID-19, flu, or RSV.

Explanation:

• Collected through the National Syndromic Surveillance Program (NSSP). The trends show changes in the percent of all visits to the emergency department that are for COVID-19, flu, and RSV.
• CDC models the rate of change and shares that it is increasing or decreasing if confident in the change based on the model. If there is no clear trend, the jurisdiction is marked "No Change." If there is not enough data to be confident of the trend, the jurisdiction is marked "Sparse."
• Read more about this data set here.

• The data used by public health comes from a wide variety of places within local communities, such as: hospitals, laboratories, doctors' offices, sewersheds, and the vital statistics office.
• These data are reported by state and territorial health departments and other data reporters. The data vary in availability due to differences in data collection/reporting practices, legal constraints and privacy protections. Health departments may not have the data or be able to share it for these reasons.
• Reporting to the CDC by state and territorial health departments is typically voluntary, as CDC does not have direct authority to require data reporting. Additionally, as of May 11, 2023, the federal COVID-19 public health emergency has ended, ending CDC's authorization to collect certain types of public health data.
• Sometimes, certain data may not be displayed on our website due to its instability or being based on small numbers.
• Learn more about CDC's efforts to strengthen data availability here.

• Wastewater testing allows CDC to monitor infectious diseases in a community, even if people don't have symptoms. By tracking virus levels in wastewater over time, public health officials can determine if infections are increasing or decreasing in an area. More detailed methods can be found in About Wastewater Data | National Wastewater Surveillance System | CDC.
• Wastewater findings may diverge from health outcome metrics, like tracking of emergency department visits, for multiple reasons. For example, wastewater data can be used as an early indicator for monitoring the spread of infection before people have symptoms or require medical care. Wastewater levels may go up (or down) before we see changes in metrics like emergency department use.
• Also, wastewater testing cannot determine the source of the viruses detected. For influenza, wastewater detections do not necessarily indicate human cases (it could be from an infected animal or animal product, like milk from an infected cow), potentially leading to the wastewater findings differing from what we are seeing in our heath outcome metrics that pertain to humans.
• Finally, wastewater testing is done on human waste disposed of through the municipal sewage system. Wastewater data will not reflect populations whose waste is disposed of outside the wastewater system, such as people wearing diapers, or households on septic tanks or otherwise not connected to a municipal sewer system.

• A Health Service Area (HSA) is a geographic area that combines one or more counties that are next to each other to form a region. The region is relatively self-contained with respect to hospital care. 
• HSAs are used to represent county-level trends in emergency department visits because patients may seek care in their own county or neighboring counties.
• The National Center for Health Statistics (NCHS), which is part of the Centers for Disease Control and Prevention (CDC), was originally responsible for defining HSAs.
• More information on HSAs is available here.

• The data available to state and local public health and the timelines for updating data may vary from what is reported to CDC.
• CDC may use different methods or tools than your state or county and will apply these methods to jurisdictions across the country allowing for more direct comparisons between jurisdictions.

• The national summary is developed by CDC experts. Each week, they review findings from multiple data systems and put this information together into messages for the public. Findings include those shared in the Community Snapshot, data from the data visualizations below, and other information that are available elsewhere on the CDC website or are not yet publicly available.

• We use two primary data sources for respiratory hospitalization rates: RESP-NET and the National Healthcare Safety Network (NHSN). By using both RESP-NET and NHSN, we aim to provide the most comprehensive view of hospitalization trends related to respiratory illnesses.
• As of November 1, 2024, the Centers for Medicare and Medicaid Services (CMS) is requiring hospitals to report information regarding COVID-19, influenza, and RSV hospitalizations, bed capacity, and occupancy to NHSN. NHSN has been added to the Illness Severity page because it has data from almost every hospital in each U.S. state. However, because these data are only required as of November 1, 2024, we also include data from RESP-NET to show longer-term trends from select hospitals across 14 states.
• RESP-NET will continue to be used on the People Most Impacted page because it provides detailed demographic breakdowns.
• Our goal is to present the most complete data regarding respiratory illness hospitalizations. By using these two sources, we ensure that users have access to both historical context and current trends across all states.

Continue exploring these data

• Respiratory Virus Activity Levels
• Severe Viral Respiratory Illness
• People Most Impacted
• Vaccination Trends

Major updates:

1. Adding new data on hospitalizations to the Severe Viral Respiratory Illness page

• What:
  • We are incorporating hospitalization rates for COVID-19, flu, and RSV as reported by all acute care and critical access hospitals in the United States to the CDC's National Health Safety Network (NHSN). These data are aggregated to the national and state/territory levels.
  • As of November 1, 2024, the Centers for Medicare and Medicaid Services (CMS) requires acute care and critical access hospitals to electronically report information via NHSN regarding COVID-19, influenza, RSV hospitalizations, and hospital bed capacity and occupancy data to CDC's National Healthcare Safety Network. For more information about reporting to NHSN, visit Hospital Respiratory Data | NHSN | CDC.
• Why:
  • This addition aims to enhance situational awareness by providing near-real-time insights into hospitalization trends associated with respiratory illnesses for both the nation and states/territories.

2. Updated the data notes for the Respiratory Virus Activity Level page

• What:
  • We added more details to the methods used for the Acute Respiratory Index baseline metric for measuring the level of respiratory illness activity.
• Why:
  • These changes will help others understand the methods and allow them to replicate the approach.

3. Design updates for greater usability in November & December 2024

• Update #1:
  • What: We added an activity level legend to the What To Know section of the Respiratory Illnesses Data Channel.
  • Why: A legend clarifies the colors used to signify activity levels and puts the current level into context for users.
• Update #2:
  • What: We changed the placement of y-axis labels on charts, so they appear at the top of the axis instead of along the left side.
  • Why: Horizontal y-axis labels are more readable and interpretable as they don't require users to read vertical text.
• Update #3
  • What: We improved the layout and design of gradient map legends and moved them above each map on the Activity Levels page.
  • Why: The improved design makes the legend easier to interpret, and when legends are placed above maps, users don't have to scroll past the map to understand the colors used.

Major updates:

1. Enhancing 'Your community snapshot’ for greater insight and usability.

• What:
  • The community snapshot now includes explanatory text for each indicator that outlines "what it is" and "why it matters" giving users a clearer understanding of the data presented.
  • Additional links allow users to access detailed data and learn more about each indicator.
• Why:
  • These enhancements are designed to provide users with essential context and background.
  • By expanding the snapshot with descriptive text and further resources, we aim to increase transparency around the data.

2. Adding new Acute Respiratory Illness (ARI) metric to capture a broader range of respiratory illnesses requiring medical care.

• What: We utilize the ARI metric to categorize the level of respiratory illnesses as Minimal, Low, Moderate, High, or Very High in two places:
  • 'Your community snapshot' on the main page of the Respiratory Illness Data Channel alongside other state and community data.
  • Respiratory Virus Activity Levels, where we replaced the map based on influenza-like illness (ILI) with a map using the new ARI metric to capture the level of respiratory illness activity across the US. ILI data continues to be available on the ILINet State Activity Indicator Map.
• Why:
  • The ARI metric provides a broader picture than ILI for evaluating overall respiratory illness trends. Some respiratory illnesses do not have fever as a main symptom and are not captured consistently in measures using ILI, which uses fever as a criterion.
  • The new summary metric characterizes overall ARI activity to monitor the combined effects of multiple respiratory illnesses and when used in combination with laboratory confirmed pathogen specific surveillance can help monitor trends in illness associated with respiratory pathogens.

3. Enhancing emergency department data.

• What:
  • We added a way to understand how often COVID, flu, and RSV is being seen in emergency departments in 'Your community snapshot.' Levels are categorized as Minimal, Low, Moderate, High, or Very High.
  • These categories are relative to a seasonal baseline (periods when circulation of the virus is low) established for each state to better account for differences in emergency department use behaviors across the US.
• Why:
  • Levels will help you see how the number of people sick enough they need to go to their local emergency room, either because of the severity of their illness or as a replacement for primary care, compared to the number of visits for those reasons when virus activity was low.
  • Emergency department data in 'Your community snapshot' previously only monitored changes in the percent of people going to the emergency department for treatment of COVID-19, flu, and RSV. With the addition of these new categories, you can quickly see current levels of activity alongside whether visits are increasing, decreasing, or not changing. The Activity Levels page will continue to show the weekly percentage of emergency department visits for each virus over time if you want to monitor more specific changes.

4. Adding new data to the Respiratory Virus Activity Levels page.

• What:
  • We are adding epidemic trend information for COVID-19 and flu to the activity levels page. The epidemic trend is measured by the effective reproduction number, or Rt a key metric that indicates whether infections are increasing (R_t > 1), decreasing (R_t < 1), or not changing (R_t ≈ 1). These data are calculated and displayed at the state level. Read more here and in the Behind the Model.
  • R_t estimates are derived from emergency department visit data reported through the National Syndromic Surveillance Program (NSSP) and are updated each week by the Center for Forecasting and Outbreak Analytics. in collaboration with the National Center for Immunizations and Respiratory Diseases.
• Why:
  • The interactive maps will allow users to visualize and understand the estimated current trends in COVID-19 and flu transmission across states.

5. People most impacted page reorganization and redesign

• What:
  • We have combined three previously separate pages into one comprehensive 'People Most Impacted' section.
  • This new, unified section provides users with a simplified view of which population groups are most affected by respiratory illnesses.
• Why:
  • Consolidation of these pages should make it easier to find relevant information.
  • By presenting a cohesive picture of impacted groups, we facilitate better understanding and comparison across different demographic characteristics such as age, sex, and race and ethnicity.

Major updates:

1. Release of data for the 2024─2025 seasonal COVID-19 and flu vaccines as well as RSV vaccination data.

• What:
  • We updated the site to show data for the 2024-25 season for adults.
  • Survey data for children will be available on the site later in October.
• Why:
  • 2024-25 COVID-19 and flu vaccines are available and can provide protection against severe disease. The data for the 2023-24 season is available on RespVaxView.
  • RSV vaccines continue to be available and are recommended for adults 75+ and adults ages 60-74 at increased risk of severe RSV. To prevent severe RSV disease in infants, CDC recommends either maternal RSV vaccination or infant immunization with nirsevimab. Additional data are available on RespVaxView.

2. Vaccination data reorganization and redesign.

• What: We made several updates to the adult and children vaccination pages, including:
  • We consolidated the adult and children vaccination pages into a single comprehensive vaccination page.
  • We created line charts displaying 2024-25 seasonal COVID-19 and influenza vaccination trends for children and adults, as well as RSV vaccination trends for individuals aged 75+.
  • We created stacked bar charts for the 2024-25 seasonal COVID-19 and influenza vaccination for vaccination status and intent with a filter option to toggle between children or adults (which will become active once data for children are available). We also created a stacked bar chart for RSV vaccination for vaccination status and intent for adults ages 75+.
• Why:
  • Centralizing vaccination information on one page simplifies navigation and provides a unified resource for users seeking both adult and children's vaccination data. The vaccination page will now contain data for children and adults in one place.
  • Additional data are available on RespVaxView.

Major updates:

1. Adding wastewater viral activity levels for influenza A and RSV.

• What: We added wastewater viral activity levels for influenza A and RSV to:
  • The 'Your community snapshot, where it can be quickly viewed alongside other helpful data about your community.
  • Activity Levels, where you can see a broader view of viral wastewater levels across the country.
• Why:
  • CDC is now releasing wastewater viral activity level data for influenza A and RSV. Wastewater monitoring can detect viruses spreading in a community whether or not people have symptoms, get tested, or go to the doctor. This will provide an additional monitoring tool as we approach the fall and winter virus season.
  • Visit the National Wastewater Surveillance System's Influenza A and RSV pages for additional data and charts.

2. Enhancing wastewater data on Activity Levels

• What: On Activity Levels, we replaced the wastewater line graph with a state-level map of United States.
• Why:
  • CDC user testing found that users preferred the wastewater Unites States map to the wastewater trend figure that had previously been displayed. The National and Regional Trends figure will continue to be available on the National Wastewater Surveillance System (NWSS) site.

3. Enhancing the weekly national summary on the Respiratory Illness Data Channel.

• What: We added the 2024-2025 Respiratory Disease Seasonal Outlook
  • CDC released the on August 29, 2024. The Outlook is based on expert opinion, historical data, and scenario modeling conducted by the Center for Forecasting and Outbreak Analytics (CFA) for COVID-19, influenza, and RSV. For additional information check out the Behind the Model.
  • CDC will update the outlook every two months throughout the fall and winter virus season and as warranted by changes in the trajectories of any of the three diseases.
• Why:
  • The Outlook is intended to provide decision-makers information to assist with public health preparedness, including planning for potential surges in hospital demand.

Major updates:

1. 'Your community snapshot' reorganization and redesign:

• What: We made several updates to the 'Your community snapshot' widget (county and state interactive dropdown), including:
  • We moved the 'Your community snapshot' widget to the Snapshot page.
  • We added national and state level data in addition to local data. It will now default to show national data and encourage users to drill down to local data.
  • We also updated the interface to improve usability.

• Why:
  • The Snapshot page will now be an at-a-glance overview of what is happening this week in COVID-19, flu, and RSV.

2. Adding wastewater viral activity levels to the 'Your community snapshot':

• What: We added COVID-19 wastewater viral activity levels at the national and state level to the Community Snapshot.
• Why:
  • Wastewater (sewage) can be tested to detect COVID-19 in a community. Wastewater monitoring does not depend on people with COVID-19 having symptoms, seeking medical care, or the availability of testing.
  • By measuring viral levels in wastewater over time, local public health officials can tell how the number of infections is changing in a particular area.
  • You can use these data as an early indicator that levels of infections are increasing or decreasing in your community.

3. Revamped the user interface of all pages to reflect CDC.gov's new, optimized design.