COVID-19 Wastewater Surveillance

Tracking the prevalence of COVID-19 among metro area residents

What you flush down the toilet has a lot to say about the SARS-CoV-2 virus that causes COVID-19.

People infected with the virus shed it in their feces, even if they don’t have symptoms. The virus can be detected in wastewater and serve as an early warning sign that COVID-19 is spreading within a community.

Wastewater surveillance is a tool in public health decision making and establishing mitigation strategies, especially given home testing that goes unreported. It also lays the groundwork for monitoring for other infectious diseases.

We partner with the University of Minnesota Genomics Center to extract and analyze viral genetic material, RNA, from wastewater flowing to the Metro Plant in Saint Paul.

By measuring the concentrations of the viral RNA in samples, they can assess the prevalence of the virus, the viral load, among the nearly two million people who live in the Metro Plant sewershed, the area of the region that the large treatment plant serves.

Wastewater sampling does not confirm individual cases or provide detailed information about how and where outbreaks occur. But it is an unbiased measure of disease prevalence in a sewershed.

This week's data

The most recent data update includes samples taken May 15 – May 21, 2023. During this sampling period:

  • The total viral RNA load entering the Metro Plant decreased by 36% last week compared to a week earlier.
  • The load is now 90% lower than it was in mid-February and lower than it has been since mid-March 2022.
  • XBB remained the dominant variant in wastewater entering the plant last week.

See an interactive version of this information or download data

Total viral load

This graph shows the amount of SARS-CoV-2 viral RNA entering the Metro Plant each day (light blue dots) and averaged over the preceding 7 days (thick blue line). The gray area shows the number of new daily COVID-19 cases in the Metro Plant's service area, by sample collection date averaged over the preceding 7 days. The most recent case data (darker gray) are incomplete and subject to change. COVID-19 case data are from the Minnesota Department of Health. Last wastewater sample date was May 21, 2023.

This graph is interactive: hover over points for more information, or click and drag to zoom in.

This graph shows the amount of SARS-CoV-2 viral RNA entering the Metro Plant separately for each variant. The viral load for each variant is estimated by multiplying the total viral load by the frequency of that variant. Because measured frequencies do not always add to 100%, the sum of all variant loads may be slightly greater or less than the total viral load. The loads of Omicron BA.4 and BA.5 are shown as the sum (BA.4+BA.5) before May 31, 2022, and separately afterwards. Last wastewater sample date was May 21, 2023.

This graph is interactive: hover over points for more information, or click and drag to zoom in.

Download data

This graph shows the percentage of SARS-CoV-2 viral RNA that can be attributed to each variant. Variants are tracked by sequencing marker gene mutations on the SARS-CoV-2 viral genome. Omicron BA.4 and BA.5 are shown as the sum (BA.4+BA.5) before May 31, 2022, and separately afterwards. Because each variant is measured separately, variant frequencies do not always sum to 100%. Last sample date was May 21, 2023.

This graph is interactive: hover over points for more information, or click and drag to zoom in.

Download data

Learn more

Wastewater surveillance addresses need for public health data

The Met Council samples wastewater flowing into four of the region’s nine treatment plants. The most prevalent data come from the Metro Plant, which treats the wastewater of 66 communities in five counties. Scientists there initially launched the initiative to be of assistance to the health department in the fight against COVID-19.

For more information on wastewater surveillance for SARS-CoV-2, visit the CDC website.

We update the dashboard data every week on Friday mornings. The data provides information on the prevalence of the virus during the week that precedes the data release. In other words, if the data are released on the 20th of the month, the reported data are from the 10th through the 16th of the month.

Wastewater treatment is our primary business, but we are committed to helping to monitor the viral trends we’re experiencing. Wastewater surveillance has proven to be a valuable tool in the battle against COVID-19, and we are committed to continuing our efforts in this area.

Our observations are that, due to sometimes large variability in the day-to-day data, the weekly update gives a better picture of the developing trends than we would observe in a more frequent review of the data.

Viable (infectious) virus has not been detected in treated effluent from wastewater treatment plants. Modern wastewater treatment methods remove the virus before the treated water is discharged to receiving waters.

While SARS-CoV-2 can be shed in the feces of individuals with COVID-19 and discharged into wastewater collection systems, there is no evidence to date of COVID-19 infections arising from direct exposure to treated or untreated wastewater.

The Met Council does not provide guidance on health-related policy or procedures with respect to COVID-19. That information is conveyed by the Minnesota Department of Health and the national Centers for Disease Control and Prevention.