The flush of a toilet is usually paid little mind once its contents disappear into the maze of pipes that converge at a municipal facility to be processed. But that wastewater may prove to be a valuable resource in combatting the COVID-19 pandemic, according to researchers at Montana State University.

A team lead by MSU scientist Blake Wiedenheft was able to detect the novel coronavirus in samples taken at Bozeman's Water Reclamation Facility, which handles millions of gallons of wastewater produced each day by the city's roughly 50,000 residents.

Seven sewage samples, taken during a 17-day period in March and April, revealed levels of the virus that tracked with a rise in the number of COVID-19 cases reported in the Bozeman area and then declined after state-mandated social distancing. That suggests that the wastewater measurements are a reliable indicator of the local prevalence of the disease, Wiedenheft said.

"This may be one of the most important indicators to follow," said Wiedenheft, associate professor in the Department of Microbiology and Immunology in MSU's College of Agriculture. "Our hope is that this approach will become more common and that communities can use wastewater monitoring as an early warning sign of coronavirus infections."

Because it's thought that individuals can be sick with COVID-19 and spread the disease for up to two weeks before showing symptoms, being able to detect increased levels of the virus in wastewater could help health officials make decisions about social distancing and other containment measures before a tide of sickened patients arrive at hospitals seeking testing and medical treatment, Wiedenheft noted.

At the end of April, Gallatin County — including Bozeman — had reported a total of 146 COVID-19 cases, suggesting that the MSU team's tests detected virus molecules from a relatively small number of infected individuals.

"One of the biggest questions right now is whether we can translate the prevalence of the virus in wastewater into an estimate of the actual number of people who are infected," Wiedenheft said, adding that his lab is currently working with other researchers at MSU on experiments that could help provide answers.

The idea for the study came from MSU researchers in assistant professor of microbiology and immunology Raina Plowright's lab who gather feces and urine from bats to study how the animals transmit viruses such as Henipavirus to humans. Plowright was aware of earlier studies indicating that people infected with COVID-19 similarly shed the coronavirus. Collaborating as part of a team of MSU scientists responding to the pandemic, the bat researchers suggested that Wiedenheft try a wastewater study in his lab, which normally studies how viruses infect bacteria.

Wiedenheft said he was skeptical. "As I was driving down to wastewater plant to collect a liter of wastewater from the millions of gallons processed by this facility in a single day, it seemed unlikely that we'd have the required sensitivity," he said.

Although preparing the wastewater samples involved a labor-intensive filtration process, the rest of the procedure was essentially the same as testing a nasal swab from a sick patient, said Wiedenheft, who was part of an MSU team that recently repurposed some of MSU's genome-analyzing research equipment to expand patient testing capabilities at Bozeman Health Deaconess Hospital.

According to an article published in early April in the journal Nature, more than a dozen research groups around the world are studying the coronavirus in wastewater. Wiedenheft's study, described in a paper co-authored with six others in his lab and published in preliminary form on April 20, is among the first to document coronavirus levels in wastewater in relation to infection rates.

Additionally, several students in the Wiedenheft lab mapped portions of the genome of the coronavirus found in Bozeman's wastewater and found that the genetic sequences matched strains that are currently circulating in New York City and originally came from Europe, Wiedenheft said.

Documenting the different strains could provide additional useful information to health officials and could help with estimating the total number of COVID-19 cases in a community, according to Alex Washburne, a research scientist in Plowright's lab. He co-authored a preliminary paper in April with researchers at Penn State University and Cornell University that correlated a rise in COVID-19 cases nationwide with the number of flu tests that reported negative results.

"We think that wastewater can be particularly useful as an estimate of overall change in COVID-19 cases in a community," Washburne said. "If we see that number starting to go up, we can turn on other monitoring systems," such as more widespread individual testing, he said.

Jason Carter, MSU vice president for research, economic development and graduate education, said that the study "is yet another example of the rapid innovation that our faculty are applying to the COVID-19 pandemic. This research has real potential to inform public health officials and help our community."

Wiedenheft said there are likely to be technical challenges that come with scaling up the approach. Still, he said community leaders and officials from around the state and world have been contacting his team to learn more. "These people want what’s best for their communities, and if wastewater can be used as one of the metrics for monitoring the outbreak, then this has important impacts for health of our citizens and health of our economy," he said.

Members of the Wiedenheft lab who contributed to the study are Murat Buyukyoruk, graduate student; Anna Nemudraia, postdoctoral fellow; Artem Nemudryi, postdoctoral fellow; Kevin Surya, graduate student; Tanner Wiegand, graduate student; Royce Wilkinson, research assistant professor of microbiology and immunology.