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Every day, roughly 170 million gallons of wastewater from dozens of communities pass through the St. Paul Metro Plant, the Twin Cities largest wastewater treatment plant.

Before the plant cleans the wastewater and discharges it into the Mississippi River, staff collect daily samples that provide a window into Minnesotans health.

Small plastic containers containing murky brown liquid are sent to a Minnesota Department of Health lab. There, researchers analyze them for COVID-19 and other viruses.

Scanning wastewater for pathogens that cause diseases isn’t a new idea. Researchers used it to look for the polio virus in the 1940s. But before the COVID pandemic, it wasn’t routinely done for public health purposes.

Scientists and public health officials saw the value of getting a sneak peek of where the virus was spreading, and where the next hot spot might be. The pandemic jump-started the development of wastewater surveillance methods that could help predict outbreaks of disease.

In spring of 2020, two professors at the University of Minnesota Medical School in Duluth, Richard Melvin and Glenn Simmons Jr., wanted to know whether they could 

 before it started showing up in positive tests at clinics. 

“At a state level, we’re able to get somewhere in the realm of like 15 days ahead of time – before whatever shows up in clinical cases, we’re able to see that in the wastewater,” Simmons told MPR News in 2021.

That lead time is valuable for hospitals, clinics and communities to prepare for surges of illness.

Steven Balogh and George Sprouse were among those intrigued by the concept. They worked for the Metropolitan Council, which operates nine treatment plants in the Twin Cities metro. 

Sprouse, a manager in the Met Council’s Environmental Services, said staff at the plants were already taking daily wastewater samples to make sure the plants were operating properly.

“But this idea of measuring genetic material to identify potential diseases — that was new,” he said.

Balogh, a principal research scientist who retired last year, said prior to the pandemic, some places in Europe were scanning wastewater for illicit drugs. Early in the pandemic, the focus pivoted to using the surveillance to track COVID, he said.

For a while, the Met Council sent samples to a Massachusetts company. But Balogh said they decided they could get data faster for less cost by doing their own analysis.

He reached out to Kenny Beckman, director of the University of Minnesota’s Genomics Center. They agreed to work together on a process.

Balogh developed a method to extract a nucleic acid called RNA from the wastewater. The Genomics Lab then used a technique called droplet digital PCR to detect the virus.

They started monitoring in November 2020, as COVID was surging. Balogh said they watched the wastewater data reflect a spike in positive cases, then a month later, a falling trend.

“By December, really, we were looking at it, saying, ‘Hey, I think this works,’” Balogh said.

Wastewater offered some advantages over other forms of monitoring. People can start shedding the virus before they know they’re sick or show any symptoms. 

And it allowed health officials to keep tracking COVID even after many people stopped going to clinics to get tested, Beckman said.

“The really critical advantage of wastewater is that once people start to do home testing and stop reporting their results, you lose that information,” he said.

Also, as the virus mutated, researchers were able to identify new strains in wastewater, such as Delta and Omicron, Beckman said.

During the height of the pandemic, people were hungry for the real-time information wastewater provided. Schools used the data to decide whether to meet in person. Families used it to gauge whether it was safe to gather for holidays.

Craig Helmstetter is managing partner of the 

 His team analyzed the wastewater data and found it correlated strongly with hospitalizations. They began regularly tracking the data and using it for reporting on COVID trends.

“It was a welcome addition to the variety of data that we were looking at to try to get a handle on what was going on with the pandemic,” he said.

Helmstetter said in the beginning, some people found the “ick” factor of wastewater humorous.

“I think even among us, it’s a novel source,” he said. “There were various emojis used in social media … But that aside, it did become an important and serious way to look at what was a very serious thing happening and still happening in our state.”

Graph of COVID-19 levels measured in Minnesota wastewater treatment plants

Today, the Minnesota Health Department and U of M Medical School collect and analyze wastewater from more than 40 plants across the state. The U.S. Centers for Disease Control and Prevention also launched a national surveillance system.

Scientists and public health officials say as a leading indicator, wastewater surveillance is one more tool they can use to get a clearer picture of what’s making people sick, and what new public health threats may be looming on the horizon.

But they caution there’s still a lot they don’t know about the relationship between wastewater and certain illnesses. 

For starters, not everything that ends up at wastewater plants comes from humans. They also receive industrial or animal waste, said Stephanie Meyer, a supervisor in the state health department’s infectious disease division. 

And it’s not always clear how long people continue to shed a virus even after they’re no longer transmitting it to others, she said.

“We never want to use it to say, ‘Wastewater is indicating this, therefore there must be a giant outbreak happening of this disease,’” Meyer said. “That may not be true and it may not be accurate.”

Rather, along with reports from hospitals, clinics, emergency rooms and other information, wastewater is “an important piece of the puzzle,” she said.

Researchers at the state health department and U of M Medical School still screen wastewater for COVID. But they’re also looking for emerging viruses, such as avian influenza and Mpox.

Mark Osborn is an associate professor at the medical school’s pediatrics department with a background in cell and gene therapy. He said they’re working on a broader scan for different pathogens, a sort of “trip wire” that could indicate a public health concern.

“That’s where I think the power will continue to be is rapid and early detection of new agents that might impact the community,” Osborn said.

Correction: (March 23, 2025) An earlier version of this story misspelled the name of Yabing Nollet in a caption.

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Kirsti Marohn

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Before the COVID-19 pandemic, wastewater sampling wasn't routinely done for public health purposes. But as the case number climbed scientists and public health officials saw the value of getting a sneak peek of where the virus was spreading, and where the next hot spot might be. 

Before the COVID pandemic, wastewater sampling wasn't routinely done for public health purposes. But as the case number climbed scientists and public health officials saw the value of getting a sneak peek of where the virus was spreading, and where the next hot spot might be.

COVID boosted efforts to track diseases in wastewater

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