To better understand the spread of COVID-19 in Wisconsin, we are testing samples of wastewater across the state to look for SARS-CoV-2, the virus that causes COVID-19. This project is a collaboration between the Wisconsin Department of Health Services, Wisconsin State Lab of Hygiene, and the University of Wisconsin-Milwaukee.
Why are we monitoring wastewater?
Monitoring wastewater is used for early detection of COVID-19 within a community. For people with COVID-19, the virus can be detected in their feces shortly after they are infected with the virus, even before they experience symptoms or if they are infected but asymptomatic. By testing wastewater, we can measure the amount of the virus and see whether the levels are increasing or decreasing. This can be an early warning sign of increasing COVID-19 cases within a community.
Currently, we track COVID-19 cases in communities by testing people experiencing symptoms or those who have been in close contact with someone who has tested positive. While testing is a crucial tool to help track the spread of the virus, it does not capture the full extent to which COVID-19 is present within a community.
Wastewater monitoring does not replace traditional COVID-19 testing, but can provide a broader understanding of COVID-19 activity. Local public health officials can use this information to make decisions to help slow the spread of the disease in their communities.
How does wastewater monitoring work?
Wastewater samples are analyzed by the Wisconsin State Lab of Hygiene and University of Wisconsin-Milwaukee to determine the amount of SARS-CoV-2 virus (the virus that causes COVID-19) present. The amount of virus, measured as viral gene copies, can indicate if COVID-19 is increasing or decreasing in a community.
How can monitoring wastewater improve public health?
Wastewater monitoring can:
- Serve as an early warning of COVID-19 in communities.
- Provide information that can help local communities intervene more quickly with mitigation strategies to slow disease spread.
- Help communities see how well protective measures (for example: quarantine, face coverings, business limitations) are working.
Where is wastewater monitoring being done?
Wastewater samples are being collected at sewersheds around the state, including in both large and small cities (sample sites are shown in the map below). The goal is to eventually include 100 sewersheds, which will cover nearly 60 percent of Wisconsin's residents.
Please note we are still gathering this information for some sewersheds throughout the state. We will be adding sewersheds to this dashboard as this information becomes available.
Select a location on the map below to see wastewater monitoring results and daily COVID-19 case rates for each sewershed.
Acronyms used on this dashboard
MSD = Metropolitan Sewerage District; WWTF = Wastewater Treatment Facility; WWTP = Wastewater Treatment Plant; WPCC = Water Pollution Control Center; WPCF = Water Pollution Control Facility; MGC = Million Gene Copies
Understanding our data: What does this dashboard show?
This interactive dashboard includes:
- Wisconsin sewershed locations and boundaries that are included in the monitoring network.
- Levels of SARS-CoV-2 virus gene copies in the wastewater, normalized by sewage flow and sewershed population.
- Daily new COVID-19 case rates within the chosen sewershed.
A sewershed is an area of land where raw sewage from homes and businesses flows through a series of sewer pipes into a single downstream point, where it enters a wastewater treatment facility.
The list on the left shows whether the amount of virus in the wastewater is increasing, decreasing, or staying the same for a particular sewershed.
Changes in SARS-CoV-2 levels in wastewater are categorized based on whether or not recent measurements have increased, decreased, or stayed the same. These categories are calculated from the slope of a linear regression, and show the percentage that the values have changed over the past five measurements. The categories include:
- Major increase (more than 100%)
- Moderate increase (10% to 100%)
- No Change (9% to -9%)
- Moderate decrease (-10% to -100%)
- Major decrease (more than -100%)
Case trajectory trends are calculated if the change from the prior 7-day period to most recent 7-day period is greater than or equal to a 10 percent change, and is statistically significant (p-value is less than 0.025).
An increase in virus gene copies over time shows that cases may be increasing in the community. Because each community is different, you should not compare viral gene copy numbers between communities. Looking at trends over time in a specific community can be used to help understand whether cases or hospitalizations are likely to increase in the future.
The wastewater concentration of SARS-CoV-2 figure can now be viewed with a linear or a logarithmic (log) scale. These two options are displaying the same values, but with different scales on the y-axis of the figure.
- A linear scale can be most helpful when data points are in a narrow range and there isn't much variability between them.
- A log scale can be most helpful when there is a large range of values in the data. Because there is a large range of values in the wastewater data, a log scale may be more helpful to see trends over time in certain sewersheds.
Benefits of monitoring for SARS-CoV-2 in wastewater
- People with COVID-19 begin to have the virus in their feces shortly after they catch the virus, sometimes days before they would begin to show symptoms or get tested.
- Increases of viral gene copies in wastewater have been seen up to a week before corresponding increases in diagnosed cases seen through testing.
- By seeing a rise in cases earlier, local public health interventions can be implemented sooner. This can then help limit COVID-19 spread in a community.
- Rather than test every single person individually, this approach allows monitoring of entire communities at the same time.
- It captures those without symptoms and people that may not go in for testing. This provides a more complete picture of COVID-19 activity in a community.
Limitations of monitoring for SARS-CoV-2 in wastewater
There are several limitations to wastewater surveillance, which is why we recommend following trends over time:
- Population migration. The people that contribute to a sewershed may vary from day-to-day, as they travel in or out of a sewershed for work or tourism.
- Uncertainties in shedding of the virus. The amount and how long people shed the virus is still unclear. Since it is still unclear how much virus people shed, we cannot use wastewater results to estimate the number of people with COVID-19.
- Variability of samples and analysis. The laboratories analyzing results from the sampled sites work closely with the CDC to ensure best methods are used. However, because these methods are new, they will likely change and improve over time.
About our data: How do we measure this?
We are still learning about when and how much virus is in the feces of people with COVID-19. Therefore,you should only look at the trends of viral gene copies over time. The data in the dashboard shows the total number of viral gene copies detected in the area from which the wastewater was collected.
Because people can have the virus in their feces for 20 to 30 days after they are no longer contagious, decreases in the number of viral gene copies in wastewater might lag behind decreases in cases in a community. You should take the number of viral gene copies in wastewater into account along with community case numbers and other COVID-19-related data to inform decisions about taking actions to help limit COVID-19 spread.
Can I compare results from one community with another?
We do not recommend comparing the number of gene copies found between communities. The flow of wastewater is not all the same, and sources of wastewater flow are different in each community (for example: industrial discharges or rainwater). It is better to use data from a single location to see trends over time. However, you may compare trends between different locations.
The data in this dashboard will be updated at least twice per week.
- SARS-CoV-2 concentration data are from the Wisconsin COVID-19 Wastewater Surveillance System.
- Case data are from the Wisconsin Electronic Disease Surveillance System (WEDSS).
You stop the spread
There is no way to ensure zero risk of getting COVID-19. However, you can do certain things to help protect yourself and others.