Release Notes & Frequently Asked Questions

Overall respiratory illness activity

Summary:

• Shares whether the amount of people going to the doctor for respiratory illness-related symptoms of fever plus cough or sore throat is minimal, low, moderate, high, or very high

Explanation:

• Collected through the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet). Despite the name, the definition of influenza-like illness (ILI) is not limited to specific illnesses. ILI includes all visits that present with the symptoms of fever plus cough or sore throat.
• Activity levels in a jurisdiction are based on comparing the ILI visits for the current week against the average ILI visits for weeks when flu is low. The activity levels are based on how different the current week is from the "normal" non-flu weeks.
• Learn more about how this is calculated here.

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. It may show changes in disease trends earlier than data from clinical cases. Wastewater surveillance can complement other existing human surveillance systems to monitor respiratory viruses.
• The wastewater viral activity level (WVAL) is available for SARS-COV-2 (the virus that causes COVID-19) present in samples of wastewater taken from sites across the United States. Increased wastewater viral activity levels may indicate increased risk of infection in an area. More detailed methods can be found in About Wastewater Data | National Wastewater Surveillance System | CDC.
• Wastewater monitoring data are not available in all communities or in areas that are not connected to a wastewater treatment system. Jurisdictions with insufficient information are not shown.

Emergency department visits

Summary:

• Shares changes in the number of people going to the emergency department for treatment of COVID-19, flu, and 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 the model is confident in the change. If there is no clear trend, the jurisdiction is marked "No Change." If there is not enough data to be confident in 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.
• Reporting to the CDC is voluntary, 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.
• Learn more about CDC's efforts to strengthen data availability here.

• National illness activity, based on the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet), includes all visits that present with the symptoms of fever plus either a cough or sore throat. Activity levels in an area for the current week are based on comparing the number of visits for influenza-like illness (ILI) symptoms against the average number of ILI visits for weeks when flu is typically "low".
• In contrast, wastewater (sewage) is tested for specific viruses, such as SARS-CoV-2 (the virus that causes COVID-19). Wastewater testing allows CDC to detect infectious diseases circulating in a community, even if people don't have symptoms. By measuring virus levels in untreated wastewater over time, public health officials can determine if infections are increasing or decreasing in an area. Levels that are relatively close to what the area normally sees are considered "Minimal" or "Low" while levels that are much higher than the area normally sees are "High" or "Very High." More detailed methods can be found in About Wastewater Data | National Wastewater Surveillance System | CDC.

• 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 are available here.

• CDC receives data from the states, and states may publish data earlier or on different dates than CDC does.

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

Continue exploring these data

• Respiratory Virus Activity Levels | Respiratory Illnesses | CDC
• Severe Viral Respiratory Illness | Respiratory Illnesses | CDC
• Groups Most Impacted—Emergency Department Visits | Respiratory Illnesses | CDC
• Groups Most Impacted—Hospitalizations | Respiratory Illnesses | CDC
• Groups Most Impacted—Deaths | Respiratory Illnesses | CDC
• Vaccination Trends—Children | Respiratory Illnesses | CDC
• Vaccination Trends—Adults | Respiratory Illnesses | CDC

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 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.