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A closely watched indicator of coronavirus trends had been falling, but is it about to turn upward again?

Wastewater at the Deer Island plant is being studied to see how much coronavirus is present.
Wastewater at the Deer Island plant is being studied to see how much coronavirus is present.Lane Turner/Globe Staff

The amount of coronavirus detected in wastewater at the Massachusetts Water Resources Authority’s Deer Island treatment plant had been falling, but in the most recent tests it ticked up slightly.

The new results come as the state is climbing down off its second surge, but there are concerns that new coronavirus variants arriving from overseas could push cases back up. Officials say that underscores the need to get the state’s residents vaccinated.

The pilot program looks for SARS-CoV-2 RNA copies per milliliter of wastewater. Officials are hoping the tests can serve as an early warning system for virus surges. Cambridge-based Biobot Analytics, which conducts the testing, says it has found that the amount of virus in the wastewater is correlated with newly diagnosed coronavirus cases four to 10 days later.

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The company says its tests will detect both the current version of the virus and new variants.

Like other coronavirus metrics, the wastewater data have shown two major surges, one in the spring and one in the fall, which had been on the decline for about two weeks, except for the latest uptick. The latest results cover tests conducted through Saturday.

The MWRA releases results for both the northern section of the system, which includes Boston, and the southern section.

A model from the University of Massachusetts suggested Tuesday that daily case counts will decline in the next several weeks, while death counts will decline more gradually. Still, the deaths will take a steady toll. The ensemble, or combination, model from the lab of Nicholas Reich predicts the total number of confirmed and probable coronavirus deaths in Massachusetts could rise to about 16,000 by Feb. 20, though researchers noted the number could range from 15,530 to 16,397.

Michael T. Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, warned Tuesday on MSNBC that the “very worst of the pandemic is yet before us.” He said the variants pose a “huge challenge.” He said he was “not at all optimistic.”

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The current national improvement in coronavirus statistics could be “a dip that’s going to occur before the huge surge,” he said.



Martin Finucane can be reached at martin.finucane@globe.com.