Steady COVID-19 case counts may be concealing growing concentrations of the virus around the Midcoast, according to municipal wastewater testing data.

After declining throughout the month of August, concentrations of virus fragments in samples of Cumberland County and Sagadahoc County wastewater spiked during the first weeks of September.

On Sept. 15, the most recent date with available data, Brunswick’s “effective virus concentration” was 2.57 million viral copies per liter of water, more than three times the current national average. On the same day, Bath’s sample showed an effective concentration of 1.41 million viral copies per liter, nearly double the national average.

Results from individual wastewater samples can fluctuate dramatically and should be taken with a grain of salt, according to Robert Long of the Maine Center for Disease Control. Yet longer trends, like those in Cumberland and Sagadahoc County, can signal that COVID-19 is on the rise.

Earlier this year, the Maine and U.S. Centers for Disease Control launched wastewater testing programs at 24 sites across the state. Twice each week, Bath and Brunswick send samples to Biobot Analytics, a Massachusetts lab that analyzes the wastewater and produces a public report detailing its viral concentration.

As mandatory testing programs have closed and home antigen tests have become more easily accessible, the number of COVID tests reported each day to the CDC has dwindled since the height of the Omicron surge last winter, according to department data.


That trend has made wastewater testing a vital tool in tracking the presence of the virus, said Robert Wheeler, a professor in the University of Maine’s molecular and biomedical studies department.

“It’s something that I look at every day,” said Wheeler, who coordinates the University of Maine’s own wastewater testing system. “It’s a really important surveillance tool.”

It’s impossible to translate the concentration of viral fragments in wastewater into a specific number of sick individuals because different people shed the virus at different rates, Wheeler said. Yet observing general trends can help people make informed decisions about current risk levels in their communities.

For example, Wheeler originally asked his students to wear masks at the beginning of the semester but removed the requirement after the university’s wastewater showed the concentration of the virus was declining.

While local wastewater data might inspire Midcoast residents to opt for more caution, it’s not a crystal ball, Wheeler warned. The likelihood of another surge in cases this winter could depend on the emergence of a new variant, a possibility Maine CDC Director Dr. Nirav Shah did not rule out at a panel discussion in Freeport last month.

Health professionals recommend Mainers sign up to receive their second booster shots in order to protect themselves from the virus.

“The COVID-19 vaccines, including boosters, continue to save countless lives and prevent the most serious outcomes (hospitalizations and death) of COVID-19,” FDA Commissioner Robert M. Califf said in an August 31 press release. “As we head into fall and begin to spend more time indoors, we strongly encourage anyone who is eligible to consider receiving a booster dose.”

For a list of vaccination sites visit the Office of the Governor’s website at

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