COVID levels in waste water in Eastern Mass. climb — but at a slower pace

The levels of coronavirus in Eastern Massachusetts waste water, considered an early warning for future COVID-19 case increases, continued to climb through the weekend, but the pace of increase appeared to slow.

Virus levels were nearly flat Sunday through Tuesday in both the northern and southern regions of the Massachusetts Water Resources Authority, which released the data.

The levels have fallen precipitously from heights reached early this year as the Omicron wave peaked. They bottomed out around the beginning of March. They have been rising gradually since, though they are still just a fraction of their peak.

COVID-19 case numbers in Massachusetts have also been rising, though they’re still far below the last peak. A number of experts have said they expect increases in cases due to the BA.2 subvariant, but not a major surge. Experts are also keeping an eye on new versions of the virus such as BA.2.12.1.

Waste water from 43 communities, including Boston, converges at the MWRA’s Deer Island plant on 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.

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.

The authority released five days’ worth of test results on Wednesday.

For the southern MWRA region, the seven-day average was 675 copies/mL as of Tuesday. 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 also 675 RNA copies/mL as of Tuesday, up from 101 on March 9. The levels peaked at 8,644 on Jan. 5.

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