Blake Wiedenheft

Blake Wiedenheft is one of the researchers behind efforts to track COVID-19 in wastewater.

The answer to the question of how prevalent the coronavirus is in Gallatin County might come from an unlikely place — the sewer.

Researchers at Montana State University have been tracking the virus that causes COVID-19 through samples from Bozeman’s wastewater treatment plant on Springhill Road.

Between March 30, when the researchers began collecting samples, and April 6, they found the concentration of the virus in the wastewater generally declined, said Blake Wiedenheft, who is leading the research and is an associate professor in the MSU Department of Microbiology and Immunology in the College of Agriculture.

By April 8, the concentration of the virus was below detectable levels and has remained there since.

“This information is really important because it can serve as a sentinel,” Wiedenheft said. “Now that the virus is no longer detectable, the question is when is it coming back. I think wastewater can answer that question.”

Wiedenheft’s lab began collecting wastewater samples after the governor’s stay-at-home order went into effect on March 28, so his data can’t give a complete picture of whether the policy slowed the spread of the virus. However, because the concentration of the virus in Bozeman steadily declined while residents stayed home, it is likely the order was effective, Wiedenheft said.

“I think the aggressive and progressive actions by the governor have worked and allowed us to start opening up,” he said.

Wiedenheft has been sharing the results with the Gallatin City-County Health Department, which is using them as part of its broader effort to monitor the virus.

“Wastewater is a contemporary canary in the coal mine,” Wiedenheft said. “With a single sample, we can get a sense of the virus in the community.”

Seth Walk, also an associate professor in the Department of Microbiology and Immunology, is expanding on Wiedenheft’s work. His lab is planning to collect and analyze samples from wastewater plants in Big Sky and Belgrade beginning next week. Additional plants, such as those in Three Forks and West Yellowstone, might be added later.

“We hope to measure in different places in the county to see if cases go up with reopening or as visitors start coming in and tourism ramps up this summer,” said Walk, a member of the Gallatin City-County Board of Health. “We can see if the number of cases reported based on testing at the hospital is reflected in the wastewater. It’s a way to feel more confident about what’s happening.”

Wastewater data may also address some of the limitations of individual testing. People can be sick with COVID-19 before they have symptoms or they can be asymptomatic, but the virus still appears in their stool, Walk said. Testing has also been limited, so wastewater samples may be a more realistic way to track the virus’ spread.

One of the biggest questions remaining is whether researchers can correlate the concentration of the virus they find in wastewater to the number of infected people. The correlation involves several variables, including how much virus people shed in their stool, how long they shed the virus after they recover from the disease and how the flow rate of wastewater fluctuates over time. Wiedenheft’s lab is working to make this correlation.

“Some people are extrapolating the amount of virus to the number of cases, but right now, those numbers are just a guess because there are a lot of unknowns,” Walk said.

Wastewater monitoring has been used for years to track viruses. Many researchers — not just those in Bozeman — are now using it to track the virus that causes COVID-19.

Biobot Analytics, a Massachusetts-based company, is analyzing samples from more than 100 wastewater treatment plants in 30 states to inform cities’ and towns’ decisions on when to loosen social distancing requirements. In Montana, Livingston and Great Falls are working with the company.

Using the company is more expensive than having researchers at MSU do the work in Gallatin County, Walk said.

Wiedenheft has received money from MSU for the work he has done and said he is hoping to receive funding from the city of Bozeman to continue the wastewater monitoring. Walk said he plans to ask Gallatin County for money to monitor the towns outside Bozeman.

Perrin Stein can be reached at or at 582-2648.