About Wastewater Data

Wastewater monitoring data are most useful when used with other data, such as hospital visits or clinical testing data. Wastewater data are primarily used in four ways:

• Monitoring for the presence of infections in a community, regardless of whether the infections cause severe illness, mild illness, or no symptoms at all. By acting as an early warning system, wastewater monitoring can detect small changes early and take quick action to prevent further infections.
• Tracking trends in infection in a community whose sewage flows into a wastewater treatment plant (known as a sewershed).
• Tracking infection trends within a state, region, and nationally.
• Monitoring variants of a virus that are causing infections in a community.

More data over time can give health departments better, more reliable insights into trends that are happening in a community, state, region, and the nation. Public health officials watch for sustained increasing levels of viruses and bacteria in wastewater and use these data to inform public health decisions. State and local health officials track a variety of data and put this information together to understand the local situation and decide how to best respond.

Wastewater monitoring can detect viruses spreading from one person to another within a community earlier than clinical testing and before they go to their doctor or hospital. It can also detect infections without symptoms. If you see increased Wastewater Viral Activity Levels of SARS-CoV-2, it might indicate that there is a higher risk of infection. See how to protect yourself from respiratory viruses like COVID-19 and Flu.

Wastewater data are updated every Friday with the previous week’s data, which allows for data to be reviewed for accuracy. Analyzed data are available for download from data.cdc.gov. The full NWSS dataset, including raw data, is available by submitting a data request to NWSS@cdc.gov.

NWSS recommends wastewater testing twice per week at each site across the United States and in territories and select tribal nations. For the latest number of sites reporting data, see About CDC’s Wastewater (NWSS) Program.

The following are more in-depth methods for how wastewater data are analyzed and displayed for:

• Wastewater Viral Activity Level for SARS-COV-2 (COVID-19), influenza A, and RSV
• Avian Influenza (H5) Detections
• SARS-COV-2 Variants
• Mpox Wastewater Data

Note:  Wastewater surveillance is an evolving science, and CDC may update methods and visualizations to improve the understandability of wastewater data.

Wastewater Viral Activity Level: SARS-COV-2, Influenza A, RSV

The Wastewater Viral Activity Level is a calculated measure that allows us to aggregate wastewater sample data to get state/territorial, regional, and national levels and see trends over time.

The value associated with the Wastewater Viral Activity Level is the number of standard deviations above the baseline, transformed to the linear scale. The formula is Wastewater Viral Activity Level = e ^{# of standard deviations relative to baseline}.

The current Wastewater Viral Activity Level for each state and territory is categorized into very low, low, moderate, high, or very high as follows:

Calculating the Wastewater Viral Activity Level

• Data are normalized based on the data that are submitted by the site.
  • If both flow-population and microbial normalization values are available, flow-population normalization is used.
• After normalization, all concentration data is log transformed.

• For each combination of site, data submitter, PCR target, lab methods, and normalization method, a baseline is established. The "baseline" is the 10th percentile of the log-transformed and normalized concentration data within a specific time frame. Details on the baseline calculation by pathogen are below:
  • SARS-CoV-2
    • For site and method combinations (as listed above) with over six months of data, baselines are re-calculated every six calendar months (January 1st and July 1st) using the past 12 months of data.
    • For sites and method combinations with less than six months of data, baselines are computed weekly until reaching six months, after which they remain unchanged until the next January 1st or July 1st, at which time baselines are re-calculated.
  • Influenza A and RSV
    • For site and method combinations (as listed above) with over twelve months of data, baselines are re-calculated every August 1st using all available data in the previous 18 months.
    • For sites and method combinations with less than twelve months of data, baselines are computed weekly until reaching twelve months, after which they remain unchanged until the next August 1st, at which time baselines are re-calculated.
• The standard deviation for each site and method combination is calculated using the same time frame as the baseline.

• The number of standard deviations that each log-transformed concentration value deviates from the baseline (positive if above, negative if below) is calculated.
• This value (x) is then converted back to a linear scale (by calculating e^x) to form the Wastewater Viral Activity Level for the site and method combination.
• The Wastewater Viral Activity Levels from a site are averaged by week for all figures.

• We calculate the median Wastewater Viral Activity Levels among sites at national, regional, and state levels, excluding data from site/method combinations with less than 6 weeks of data for SARS-CoV-2, and 10 weeks of data for Influenza A and RSV.

Data Inclusion Criteria – SARS-COV-2, Influenza A, RSV Wastewater Viral Activity Level
SARS-CoV-2: New wastewater sampling sites, or sites with a substantial change in laboratory methods are included in national, regional, state, or territorial median values once there are at least 6 weeks of samples reported for that location.

Influenza A and RSV: New wastewater sampling sites, or sites with a substantial change in laboratory methods, are included in national and state or territorial median values beginning on August 1^st of each year once there are at least 10 weeks of samples reported for that pathogen. Data must be reported by October 1^st of that year to be included in national and state or territorial median values for that respiratory virus season. If data are reported after October 1^st of that year, they will not be displayed until August 1^st of the following year.

Avian Influenza A(H5) Wastewater Data

In August 2024, CDC began publicly displaying avian influenza A(H5) subtyping results from wastewater surveillance.

View wastewater data for avian influenza A(H5)

About the influenza A(H5) virus detection metric used in wastewater: 

• The avian influenza A(H5) virus detection metric used in wastewater is calculated and displayed for individual sampling sites and reflects whether virus was detected within samples collected over the previous week.
• When multiple samples are collected, or multiple laboratories test samples from the same site in a given week and avian influenza A(H5) virus is detected in any sample collected during that week, testing at that site is classified as a detection.

SARS-COV-2 Variants

The proportion of SARS-CoV-2 variants in each sequenced sample were assigned using Freyja and averaged nationally. All lineages not enumerated in COVID-19 Variants in Wastewater dashboard are aggregated with their parent lineages, based on the Pango statement of nomenclature rules. Any variants making up less than 5% of the national weekly average were categorized into the "Other" category.

View SARS-CoV-2 variant wastewater data

Mpox Wastewater Data

Wastewater sites across the United States are testing for the virus that causes mpox (MPXV). View wastewater surveillance data for MPXV.

About the MPXV detection metric used in wastewater: The MPXV detection metric used in wastewater is calculated and displayed for individual sampling sites and reflects whether virus was detected within the samples collected over the previous 4 weeks. An individual sampling site is typically a wastewater treatment plant but may be a location in the sewershed before wastewater enters the treatment plant.

MPXV Metric Calculation:

• All samples collected over the previous 4 weeks at a site are included in the percent detection calculation. For each MPXV testing type (clade I, clade II, non-clade specific), the number of positive samples at a site is divided by the number of total samples to calculate the percent of detections at a site.
• The percent of detections at a site for each MPXV testing type are then used to categorize the site into one of 4 categories: persistent detection, detection, no recent detection, or no recent data. Most recent date of detection by site and MPXV testing type is used to determine if the site had a detection in the previous 2 weeks. See definitions for each detection category.
• MPXV laboratory detections reported on CDC's wastewater dashboard may, in some cases, fall below the stated limit of detection for the assay. Limits of detection are calculated by the laboratory doing the analysis and are specific to the assay and laboratory methodology.
• A site may appear in more than one detection category if samples from the site are tested for MPXV at different laboratories or if samples from a site are tested using more than one test type.

Wastewater samples contain a mix of DNA and RNA from bacteria, viruses, animals, humans, and other living things. CDC takes multiple steps as part of its wastewater surveillance program to ensure that the privacy of individuals contributing to wastewater is protected. CDC's wastewater program monitors infectious diseases and does not track or assess human genomic data.

Here are examples of how CDC’s wastewater program is protecting individuals’ data:

• Community-level data: Wastewater is collected from a combined, community-level sample not from an individual person or household.
• Population size: Sampling covers a large enough population that wastewater testing results for infectious diseases be associated with an individual person.
• Public data display policies: CDC will not publicly display any wastewater detections that could be used in combination with clinical diagnostic testing data to identify an individual. Locations for wastewater treatment plants are approximated. Locations may be also adjusted to allow sites within close proximity to be more easily distinguished on a map. In addition, CDC does not publicly display data that meet any of the following criteria:
  • Data from sewersheds that serve fewer than 3,000 people
  • Data from facility or institution-specific sampling locations
  • Data from tribal communities
  • Data from sewersheds with known data quality issues.
• Data privacy technology: CDC uses the publicly available NCBI Human Read Removal Tool to ensure that any potential remaining human DNA is removed. CDC receives most sequencing data via NCBI, which removes any human DNA sequences before the data is sent to CDC
• Scientific limitations: Multiple factors protect the privacy of individuals when wastewater is used for public health.
  • Wastewater contains fragments of genetic material from thousands of people, making it unlikely that any single individual could be identified.
  • Every person has their own unique genome, or DNA "fingerprint." To identify an individual, one would need to match the DNA fragments from wastewater to their DNA fingerprint. Although there is a small, theoretical chance this could happen, it is highly unlikely. CDC does not have individuals' DNA fingerprints and therefore cannot match DNA fragments found in wastewater with individuals.
• Preparing for the future:
  • CDC will continue to preserve individual privacy and prioritize data stewardship as technology evolves, including changing policies if technologies emerge that enable individual identification using wastewater data.
  • CDC will adhere to ethical standards in wastewater science [PDF – 33 pages] to ensure individual privacy is protected and public health is enhanced. CDC will work with participating communities to understand ongoing priorities and concerns.

Data collected in CDC’s National Wastewater Surveillance System may over-represent certain populations within a state or territory. For example, most jurisdictions report data from municipal sewer system samples and may have limited inclusion of populations that rely on other non-sewered sanitation systems (e.g. septic tanks). They may also over-represent urban and suburban populations because of wastewater utility locations and the associated sewershed. As a result, these data may not accurately depict the full picture of viral activity for the entire state or territory.

The data presented are preliminary and may change as more data are received. Differences in the data presented by CDC and state health departments likely represent differing levels of data reporting; data presented by the state are likely the more complete ones. Additionally, there may be differences in data visualization approaches that impact how data are displayed.

Specific wastewater data limitations for each pathogen will be available in the data footnotes or About the Data sections:

• SARS-COV-2
• Influenza A
  • Avian Influenza A (H5)
• RSV
• Mpox