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Levels of coronavirus continue to climb in waste water in Eastern Mass.

Waste water coming into the Deer Island treatment plant on Boston Harbor is tested for traces of the virus that causes COVID-19.David L. Ryan/Globe Staff

The levels of coronavirus in Eastern Massachusetts waste water continued to climb through the weekend, suggesting more COVID-19 case increases may be ahead.

The levels fell precipitously from heights reached early this year as the Omicron wave peaked. Then they bottomed out around the beginning of March. They have been rising gradually since, although they are still just a fraction of their peak, according to data from the Massachusetts Water Resources Authority.

Waste water from 43 communities, including Boston, converges at the MWRA’s Deer Island plant in Boston Harbor for treatment before being piped miles into the ocean. The water is tested for traces of the deadly virus. The MWRA reports numbers for both the southern and northern regions of its system.

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The testing determines the number of SARS-CoV-2 RNA copies per milliliter of waste water. Scientists say that tracking the levels can serve as advance warning several days ahead of case increases.

For the southern MWRA region, the seven-day average was 480 copies/mL as of Monday. That’s up from a low of 92 copies/mL on March 1. But it’s a far cry from the high of 11,446 RNA copies/mL reached on Jan. 3.

In the northern region, the seven-day average was 460 RNA copies/mL as of Monday, up from 101 on March 9. The levels peaked at 8,644 on Jan. 5.

COVID-19 case numbers in Massachusetts are also rising slowly while still below the last peak. The highly infectious BA.2 Omicron subvariant recently caused a surge of cases in Europe so officials are keeping a close eye on it as it spreads here.

A number of experts have said they expect increases in cases due to BA.2, but not a major surge.

The new White House COVID-19 response coordinator, Dr. Ashish K. Jha, said Monday that while there had been a recent uptick in coronavirus cases nationally, he was not overly concerned.

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“We were expecting this because we saw this in Europe a few weeks ago,” he said. “But the good news is we’re coming off of so very low infection numbers. Hospitalizations right now are the lowest they have been in the entire pandemic.”

“We’ve got to watch this very carefully — obviously, I never like to see infections rising — I think we’ve got to be careful,” Jha said on the “Today” show. “But I don’t think this is a moment where we have to be excessively concerned.”

The US Centers for Disease Control and Prevention estimated Tuesday that BA.2 accounts for more than 90 percent of the cases in New England and about 86 percent nationally.

Material from Globe wire services and previous Globe stories was used in this report.


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