Frequently Asked Questions

Illinois has established a monitoring network to track COVID-19 and other illnesses by measuring the amount of viral RNA in wastewater for several pathogens of public health importance. The initiative is a collaboration between the Illinois Department of Public Health (IDPH) and the University of Illinois System’s Discovery Partners Institute (DPI). Additional partners include the University of Illinois-Chicago, Northwestern University and Argonne National Laboratory. DPI has contracted with GT Molecular to manage sample collection logistics. The program aims to deliver actionable information to public health decision makers to identify trends in COVID-19, influenza, and respiratory syncytial virus (RSV) infection levels and SARS-CoV-2 variants of concern. It also supports IDPH efforts related to pandemic preparedness. This system is complementary to wastewater surveillance that DPI and its partners conduct for the Chicago Department of Public Health.

People infected with influenza, RSV, or COVID-19 may be contagious before symptoms appear and/or an individual obtains a clinical diagnostic test, which means the virus could be present and moving undetected through the community. Genetic material from the SARS-CoV-2 virus that causes COVID-19 is excreted in the feces and urine of infected people even if they have no symptoms. More research is needed to understand the exact nature of how people shed influenza and RSV viral particles in the wastewater. Wastewater treatment systems collect this sewage throughout the state, providing an efficient and anonymous way to monitor for the presence of respiratory viruses in the community.

Wastewater data are analyzed as trends over time and some wastewater samples are also analyzed by genome sequencing to detect variants circulating in a community. This provides useful information for communities where timely COVID-19 clinical testing is underutilized or unavailable. In addition, SARS-CoV-2 can be detected in wastewater before infections lead to increases in hospitalizations, providing additional evidence of COVID-19 increase in a community. Community and public health leaders can use this information to make decisions about protective actions to help limit further spread of the disease.

It is anticipated that wastewater monitoring will become more important with the increased use of at-home testing, the results of which are often not shared with public health agencies. It also provides important data during a downturn in the pandemic when clinical testing may become less frequent.

Please reach out to iwss-admin@uillinois.edu with any questions you may have.

Wastewater sampling occurs at a treatment plant or sewer that provides a sample representative of an entire community. This method ensures individual privacy and anonymity. Samples cannot be traced back to any individual or household.

The program is currently prioritizing wastewater treatment plants serving the largest population center in each Illinois county. Participation in the program is voluntary and some counties do not have wastewater treatment plants. There is no cost to the plant or local taxpayers to participate.

In accordance with guidelines from the Centers for Disease Control and Prevention (CDC), twice-weekly samples are analyzed every week to determine two- and four-week trends (up, down, or no change). The results of this analysis are discussed each week with IDPH, which in turn incorporates the trend information into its planning processes.

IDPH and local health department administrators determine how to respond to data collected from each site. Wastewater sampling will not be used alone to make policy and will complement clinical data, such as results from nasal or saliva swabs.

A non-detect means that the amount of viral RNA in the wastewater sample is below the level that can be reliably detected by the quantification methods used in a given laboratory. But a determination of non-detect does not necessarily mean that no viral RNA is present in the sample or in the system. In some cases, other components of wastewater may interfere with individual measurements, leading to an incorrect non-detection similar to false negatives that can occur from at-home and clinical testing. A non-detect does not necessarily mean that there are no infected individuals within the associated community.

No. Wastewater data alone will not drive public health interventions such as masking orders or shutdowns. Rather, we hope this is a tool for communities to use along with other resources to help protect their citizens.

When public health officials determine that COVID-19 risks are very low, it is anticipated that samples will still be useful, if only to spot new coronavirus variants that could pose new threats to our health. As the program has expanded to include other respiratory viruses besides SARS-CoV-2, wastewater sampling continues to provide a public health benefit to communities.

The Illinois Wastewater Surveillance System provides information on the levels of pathogens in wastewater that can help local communities intervene with protective measures to slow disease spread. As each of us weighs the risks of respiratory illnesses in our daily lives, we look to public health guidelines and many of us also track public data such as the case rate or hospitalizations in our communities. Wastewater trends are useful to provide information at the community level.

The Illinois Wastewater Surveillance System submits wastewater data that are published to the Centers for Disease Control and Prevention (CDC) COVID Data Tracker, where it is presented as a 15-day percent change among other metrics: CDC COVID Data Tracker.

The program occasionally experiences logistical difficulties in sample collection related to local conditions at the plant, issues with transit logistics, or observed holidays. Every effort is made to support the timely collection and shipping of samples for analysis.

While the virus that causes COVID-19 has been found in untreated wastewater, there is no evidence that anyone has contracted COVID-19 by this exposure and the risk of transmission from properly designed and maintained sewerage systems is thought to be low. For sample collectors, both CDC and the Environmental Protection Agency (EPA) recommend standard protective equipment and procedures associated with working with wastewater.

Yes! In April 2023 we began posting data for influenza A and B. We have also begun analyzing samples for RSV A/B and plan to post data soon. Additional pathogens are carefully reviewed on a case-by-case basis by the Illinois Department of Public Health.

Because each pathogen is distinct, it is not appropriate to compare their viral gene copy numbers, even at the same site. Instead, increasing or decreasing trends in SARS-CoV-2, influenza, or RSV concentrations can be used to understand if cases or hospitalizations for each pathogen are likely to increase or decrease in the community.

  1. We’ve gotten better at treating COVID-19, resulting in lower mortality and lower hospitalization rates. Additionally, most folks have some immunity (either through vaccinations, or previous infection, or both), resulting in lower hospitalization rates.
  2. Testing often occurs using at-home tests, and those are not usually reported to the CDC or local public health departments and thus are not reflected in case counts.
  3. SARS-CoV-2 viral remnants show up longer in wastewater. People can shed virus that is detectable in wastewater for several weeks, even after a clinical test result would no longer be positive. Clinical case counts only reflect test positivity on one day. A person testing positive will only show up once in clinical case data but would show up over several days to weeks in wastewater data.
  4. Shedding rates change with variants, and this can impact wastewater results.

We are working on enhancing our search function. Until then, we recommend looking for the dot on the main page closest to your home. On many individual plant pages, you can see a shaded area on the map that refers to the plant’s service area (determined by an information format shared with us by the plant called a “shapefile”).

If you live in Cook County, most of the population is served by an organization called the Metropolitan Water Reclamation District of Greater Chicago (MWRD). You can zoom in on the coverage areas for each MWRD plant to understand which plant serves your community. For example, if you live in Blue Island, you can click through the MWRD plants and zoom in to see what areas each covers. If you click on Calumet Water Reclamation Plant (WRP) you will see Blue Island in the shaded coverage area. This means that wastewater flowing from your house in Blue Island goes to the Calumet WRP for treatment. The data points you see on the dashboard for Calumet WRP are from samples taken from raw influent collected as wastewater enters the facility.

Another way to determine your plant is to search for the name of your wastewater treatment plant for your community.

Many towns and cities across Illinois are still not covered by the program. IWSS prioritizes the largest plant in each county and also recruits plants by population size to provide coverage for the most Illinoisans possible. Please reach out to us at iwss-admin@uillinois.edu with additional questions on why your community may not yet be represented.