This undated electron microscope image made available by the U.S. National Institutes of Health in February 2020 shows the Novel Coronavirus SARS-CoV-2, the virus causes COVID-19. Credit: NIAID-RML via AP

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Scientists visiting Portland’s East End water treatment plant say that the best place to determine exactly how far coronavirus has infiltrated the city is in its wastewater, WGME reported.

Infected people shed some of the virus when they go to the bathroom. Saint Joseph’s College Assistant Professor Dr. Yolanda Brooks said that testing wastewater allows a more accurate estimate of how many people are infected in large, populated areas like Portland, WGME reported.

The testing comes with Maine carrying one of the lowest infection rates in the nation. As of mid-month, Maine was one of only two states where the number of infections was declining. New Hampshire was the other. A handful of states are seeing case numbers stay roughly constant, while most are seeing cases increase.

On Wednesday, another 29 cases were reported, bringing the state’s total coronavirus cases to 3,866. Of those, 3,457 have been confirmed positive, while 409 were classified as “probable cases,” according to the Maine Center for Disease Control and Prevention reports.

But the present testing model, “The confirmed case concept that we have now, will only show the symptomatic people and those who seek healthcare. It doesn’t show those who may be asymptomatic, pre-symptomatic,” Brooks said.

The sample is slowly collected throughout the day, and then is sent to Saint Joseph’s campus in Standish for testing, WGME reported.