In this Dec. 28, 2021, file photo, a sign on a Portland shop window advises customers masks are required for entry. Credit: Troy R. Bennett / BDN

COVID-19 levels in wastewater across Maine have largely remained flat in recent weeks, although several sites in northern Maine continue to report the highest concentration of the virus, corresponding with a recent spike in cases there.

Levels of COVID-19 detected in wastewater across the state are much lower than a few months ago, according to the latest data reported by the Maine Center for Disease Control and Prevention and BioBot. But after a steady decline in late January and the first half of February, virus concentrations have remained flat in recent weeks. Several sites in Aroostook County continue to see elevated virus levels.

Health officials have touted wastewater testing as a useful tool for understanding levels of COVID-19 within communities as the increased use of at-home tests has rendered other measures, such as case counts and positivity rates, less reliable. An increase in virus concentration in wastewater could serve as an “early warning” for a spike in cases, Maine CDC Director Nirav Shah said Tuesday.

Wastewater testing continues to paint the most concerning picture in Aroostook County, where sites in Presque Isle, Houlton and Fort Kent have reported higher concentrations of the virus than the rest of the state in recent weeks. That has corresponded with higher infection rates as well — over the past week, Aroostook County has reported more than 300 virus cases per 100,000 people, nearly three times higher than the statewide rate.

Outside of The County, most Maine communities have seen a substantial decline in COVID-19 transmission since the rollout of wastewater testing was introduced in late January or early February. That has corresponded with a similar drop in reported cases and hospitalizations.

But the decline seems to have leveled off in recent weeks, with wastewater districts in Maine’s largest municipalities reporting neither massive spikes nor continued declines. In Bangor, which reported more than 2 million copies of the virus per liter of sewage earlier this winter, the concentration has fluctuated between 200,000 and 350,000 in the past two weeks.

In Portland’s East End water district, concentrations have ranged from between 75,000 and 150,000 copies per liter in the past three weeks. That is down significantly from earlier in the winter, but the past few weeks have not shown a continued decline.

Nationwide, a Bloomberg News analysis of wastewater testing data maintained by the U.S. Centers for Disease Control and Prevention found roughly the concentration of virus in the wastewater was increasing significantly in roughly a third of counties measured.