Wojciech Cwik, an operator at the Waste Water Treatment Plant on Lincoln Street in Lewiston, takes a sample Feb. 11 of wastewater he collected and puts it into a container in the plant’s lab. Each morning the plant takes a sample from both Lewiston and Auburn’s wastewater and sends it to the Maine Center for Disease Control & Prevention for analysis. Russ Dillingham/Sun Journal file

Ten months since Maine began monitoring municipal wastewater sites for signs of COVID-19, wastewater surveillance remains a novel, yet important, tool for public health, experts say.

“It really is one piece of the puzzle,” Michael Abbott, associate director of the Maine Center for Disease Control and Prevention’s Division of Environmental and Community Health, said Tuesday.

Twice a week since January, public works employees at 24 municipal wastewater treatment sites across Maine have collected wastewater samples. Those samples are analyzed by Biobot Analytics, which is the federal CDC’s contractor for wastewater testing.

When the wastewater surveillance program in Maine got up and running back in January, an omicron-driven surge in infections put a record number of people in the hospital and buried the state under a backlog of some 46,000 positive tests.

“At this point in the pandemic, case counts are not the metric of the moment,” Maine CDC director Nirav Shah said in mid-January.

“We were starting to look at, rather than, you know, tracking the number of cases every day — which we are still doing that — but rather than using that as the only indicator of where we stand with the pandemic, we’re using other measures, like hospitalizations, and look at wastewater as a supplemental,” said Abbott, who runs the agency’s wastewater program.

But this is really the first time wastewater surveillance has been used to track disease at such a massive and sustained scale, both in Maine and nationwide, Abbott said. It’s not the first time it’s ever been used, but its applications were more limited before.

“But now … it’s really caught on as a huge public health tool,” he said. “But I really feel like we’re still learning how to interpret this data.”

And in Maine, especially, where wastewater from only 24 sites is tested across the state, which Abbott said were chosen for their variability in population and location, “every wastewater system is sort of its own animal.”

Everything from how much industrial versus storm water runoff goes into the system, to the number of people hooked up to the system — Abbott said about half of Maine households are hooked up to their own private septic system — can change the data. And no two people “shed” the virus in the same way after they’ve been infected, he said.

For the sites located in smaller, rural communities — which are basically all sites except the two that serve Portland — the population size can create huge fluctuations in the data from week-to-week. More populous areas, Portland or Boston, for example, “isn’t going to make a big difference,” Abbott said.

“Whereas if you’re in a place like East Millinocket,” where Abbott estimated the public wastewater system serves “no more than a few hundred,” a few cases can make a huge difference in the data.

“If you have, say, a group coming into town on a snowmobiling weekend and they all have COVID … that can actually create a significant change in that COVID concentration in the wastewater stream, enough so it looks like a big change,” he said.

“But then the next week those few cases might be out of town or recovered or whatever. And suddenly, the concentration is back to what it was the week before.”

While those fluctuations can be “a little frustrating,” in Abbott’s words, wastewater surveillance is still a useful tool for gauging the changes in COVID in a community over time.

This is especially true considering at-home rapid antigen tests are more accessible than ever, high vaccination rates means that some people are asymptomatic and may not even be aware that they are infected and some people just aren’t getting tested.

“As a result, clinical testing data has become less dependable, but wastewater monitoring remains a reliable indicator of viral spread,” Becca Malizia, a science communications manager with Biobot, said in an email earlier this month.

“This is why wastewater monitoring will play an even more important role in continuing the spread of the virus as life ‘returns to normal,’” she said.

To get the most out of the wastewater data, Abbott says he takes the individual reports from each testing site, or looks at the county data on Biobot’s website, and looks at the trends over time, compares that with the case and hospitalization rates and how those trends stack up against regional data.

The effective virus concentration in Androscoggin County, for example, was at a relatively stable level for much of the summer and into the fall. However, recently, in the weeks following when most students returned to school, the concentration increased significantly.

Other counties in Maine have seen a similar trend. Hospitalizations have also increased, hitting 200 at the start of this month for the first time since May.

“In many places in the U.S., including in the Lewiston-Auburn area, COVID-19 transmission is substantial and sustained, likely more so than case and hospitalization data suggest,” Malizia, from Biobot, said.

But, as Abbott pointed out, effective virus concentration levels in other counties, such as Piscataquis and Oxford, have already declined. New hospitalizations have slowed as well.

That could be an indication that Androscoggin County’s is “reaching the peak of that increase and perhaps looking at a decrease,” in infections, he said.

“And that’s one of the reasons why we decided to continue with another year of doing this, … we feel like we’re starting to understand what it means,” and how to use this data, Abbott said.

Maine’s wastewater screening program is funded through June 2023, Maine CDC spokesperson Robert Long said.