Many cities are now testing their sewage for signs of the coronavirus, to track and hopefully stop outbreaks of COVID-19 before they get out of control. A UNC professor is working to ensure these techniques can reach all communities.
Rachel Noble is a professor at the University of North Carolina’s Institute of Marine Sciences in Morehead City, where she studies microbes and water quality, in the ocean and in human infrastructure. Noble’s background makes her well-suited to track the coronavirus through all the different systems used to manage wastewater.
Noble is leading a team of researchers analyzing sewage in communities across the state to eventually track and predict outbreaks of the coronavirus by looking for its genetic material. The North Carolina Policy Collaboratory awarded this group a $1.7 million grant for its work. Her colleagues at NC State are also working on a national study tracking COVID-19 in larger cities.
This work is still in the early stages. Noble’s laboratory led development of the techniques other scientists can use to consistently take, process, and verify the quality of the samples they test for coronavirus. This ensures teams across the country can standardize their experiments.
While researchers can track the amount of coronavirus in wastewater, it’s not straightforward to relate that to case counts. More work is needed to understand how much virus infected people typically shed in bodily fluids and how the sewage system can affect the concentration of virus.
“Do I have the fully digested story for you of what exactly that means? No, but we have all the pieces of the story that we need to put together to figure out what that means. That’s what doing research is all about,” Noble said.
Smaller towns pose unique challenges for the germ hunters, even in centralized sewage systems. Water use changes more with the seasons in small systems, especially in tourist areas, as well as due to weather. The greater amount of water that ultimately goes down the drain in the summer dilutes the concentration of virus in sewage.
“Some of our coastal towns can have five, 10, 20, even 50 times greater water usage from summer compared to non-tourist months,” Noble said. If researchers don’t take these changes into account, they might assume infections have gone down.
Another issue is that almost half of all homes in North Carolina aren’t connected to central sewage systems. Methods that just test for coronavirus at treatment plants would exclude them.
“That’s a huge issue. I have not cracked that nut yet,” Noble said. This is one of the top goals in her future work, especially as North Carolina has a higher proportion of residents living in rural counties than almost every other state.
It was easier to design tests for wastewater treatment plants, because most of the solid material is removed before the point where samples are taken. But these techniques aren’t simply applied to septic tanks. Septic sludge is difficult to work with because it’s much more solid and concentrated with waste.
Noble described the problem as “showers, and the laundry, and whatever you scrubbed off your vegetables – everything that goes on in a household” ends up in a septic tank. A septic sample would need to be processed before researchers could try to extract genetic material from the coronavirus.
First, the sample needs to be homogenized, so everything is evenly mixed together. Then, the solid material needs to be dissolved or removed. Noble’s lab is studying how to do this without also destroying or removing too much coronavirus.
This work could also apply to package treatment plants, which are essentially giant septic tanks. They are commonly used for facilities like nursing homes, hospitals, highway rest areas, and even small neighborhoods that can’t be connected to a central sewer system.
Facilities like nursing homes could potentially save testing resources by regularly testing their package treatment plants instead of constantly testing their whole population. Once the coronavirus appears in the plant, that would be a sign to start testing individual residents and employees.
Historically, Noble said, septic systems and package treatment plants have been black boxes. Residents don’t think of them until something goes wrong. Getting samples from tanks is disruptive.
Noble is hopeful that developing useful tests for these systems would encourage people to consider the public good regular sampling could provide and manufacturers could add features to make sampling easier.
“This could serve as a screening tool for a portion of the population that’s not really on the infrastructure grid,” Noble said.
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Matthew Diasio is a 2020 AAAS Mass Media Fellow sponsored by the Heising-Simons Foundation.