Updated 5:13 p.m.

Burlington officials are exploring how city sewage might help them find the next COVID-19 outbreak. Early results are promising, they say.

The city this week is wrapping up a pilot program it quietly undertook in August to look for viral markers in wastewater. But municipal leaders are already looking for ways to expand the program this fall.

"I'm excited about this as an early warning system," Mayor Miro Weinberger said. "I think this really has the potential to give us a sense of an outbreak starting to happen at the very early stages."

Wastewater monitoring has garnered interest around the country in recent weeks as a new way to track the virus' spread. A couple of weeks ago, the federal Centers for Disease Control and Prevention announced plans for a national wastewater surveillance database to glean insights from this developing field of public health.

Because people with COVID-19 often shed the virus' genetic information in their feces, evidence of infection flows through sewers every day. By testing sewage as it enters treatment plants or at other points in the system, health officials increasingly believe they can gauge the disease's prevalence within a community.

Megan Moir, division head of water resources, said the municipal waste stream can signal the health of city residents much like river water contains information about the ecosystem around it.

"You can tell a lot about what’s going on in the watershed — or in this case a sewershed — by sampling what’s coming out of it," she said.

Similar principles have guided earlier programs elsewhere to track opioids and polio. The hope is that any changes in the wastewater concentration of the coronavirus' genetic material can help inform decision makers and guide the city's public health response.

During the monthlong pilot, the city has sampled untreated sewage entering each of the three wastewater treatment plants once a week. Automated sampling equipment collects about a liter of fluid over a 24-hour period, which is then sent off to a laboratory for analysis.

Burlington has been using Biobot, a Cambridge, Mass., company that has contracted with hundreds of municipalities nationwide, said Carolyn Felix, an analyst for the city's innovation and technology department. The city has also sent samples to researchers at the University of Vermont and Dartmouth-Hitchcock Medical Center, which are also studying the technology.

Data from the pilot program has "really just confirmed the low prevalence of COVID-19 that we’re seeing in Burlington," Felix said.

Because each treatment plant covers a different section of the city, ongoing sampling might help identify outbreaks in a particular neighborhood. But the method appears to show the most promise when used in more targeted ways.

Campus officials in Arizona said last week that wastewater monitoring of individual buildings at the University of Arizona helped identify two undetected cases inside a particular dorm, the Arizona Republic reported. They were able to order follow-up testing of all residents to find the infected individuals — possibly preventing an outbreak.

City officials are talking to the Burlington School District and the University of Vermont and Champlain College about starting a similar program, they said.

"The way my mind is working, the more surgical interventions do seem potentially more powerful," Weinberger said.

Each sample in the pilot program costs about $1,000 and requires significant staff time, Felix and Moir said. More extensive monitoring might require employees to go into numerous manholes a couple of times per week to set and retrieve sampling equipment.

Felix and Moir emphasized that sewage monitoring is unlikely to replace other testing methods and prevention efforts. Rather, it would augment them.

Burlington isn't the first Vermont city to plumb its residents' poop for coronavirus clues. Rutland participated in an earlier, seven-week program through Biobot in April and May. At that time, the infection rate in the city was too low to be detected through the company's equipment, so officials eventually discontinued the weekly tests. Commissioner of Public Works Jeffrey Wennberg said Rutland would consider using the tests again if the region experienced a new surge of cases.

That was before the Vermont Department of Health announced an outbreak in Killington that was traced to an August 19 party at Summit Lodge.

As Burlington officials evaluate the program's potential, they must also think about how to act on this new kind of data. An early warning system only works if there's also a plan for intervention. In the University of Arizona case, Weinberger noted, officials tested everyone in the dorm using rapid antigen tests, which produce results more quickly than do the highly accurate PCR tests used in Vermont.

The city said it would coordinate any ongoing program with the Vermont Department of Health. Weinberger said he expects his staff will decide how to proceed within the next two weeks.