Levels of coronavirus detected in Eastern Massachusetts waste water have risen sharply in recent days, according to data from the Massachusetts Water Resources Authority.
Virus levels detected in both the northern and southern sections of the MWRA system rose to their highest point in months, with numbers nearly doubling since the end of November.
In the MWRA northern section, the seven-day average count of the virus reached 1,943 copies/mL on Tuesday. The number has been as high as 8,644 in January, during the Omicron surge, and as low as around 100 in March.
In the southern MWRA section, the seven-day average count of the virus was 1,867 copies/mL on Tuesday. That number had been as high as 11,446 in January and fell below 100 in March.
The last time coronavirus waste water levels were this high was at the end of January. But the numbers are far lower than they were during the Omicron surge this time last year.
Over the past 60 days, coronavirus levels in both the northern MWRA section — which includes Boston, Waltham, Bedford, Stoneham, and Chelsea — and the southern MWRA section — which includes Framingham, Hingham, Stoughton, Needham, and Quincy — have increased from the counts in the upper hundreds to almost 2,000, according to the data.
On Friday, Boston Public Schools announced a temporary post-holiday masking period because of the spread of COVID, along with the flu and other respiratory illnesses, according to a letter to parents from Superintendent Mary Skipper.
Students and staff will be asked and expected to wear a mask to school from Jan. 4 through Jan. 13 as children return to classrooms, Skipper said. The policy is not a mandate, and no one will be disciplined or sent home if they refuse to wear a mask.
Students have also been provided with rapid Antigen test kits and are asked to take a COVID test on the evening of Jan. 3 or the morning of Jan. 4 before the start of the school day, Skipper said. Staff members are asked to take a test before returning to work on Jan. 3.
“While COVID-19 numbers have been less disruptive so far this year, the combination of flu and other respiratory viral illnesses have already resulted in significant staff and student absences, and remain a cause of concern … ,” Skipper said in the letter.
Officials say waste water data from the MWRA can be an early warning signal, detecting COVID-19 infections before people get tested and the tests are officially reported.
The numbers have become even more crucial as more people are using rapid, at-home tests that don’t get reported to the state and reflected in official case counts.
Waste water from 43 communities, including Boston, converges at the MWRA’s plant on Deer Island in Boston Harbor for treatment before being piped miles into the ocean. The sewage is tested for traces of the deadly virus. The MWRA reports numbers for both the northern and southern sections of its system. The testing determines the number of SARS-CoV-2 RNA copies per milliliter of waste water.
Officials and experts have urged people to get vaccinated and to get updated boosters to protect themselves and others in the coming months. The US Centers for Disease Control and Prevention also recommends a variety of other precautions, such as increasing ventilation, avoiding people who have COVID-19, and isolating if you have a suspected or confirmed case.
The number of positive COVID-19 tests in Boston is currently higher than officials would like, according to data from the city’s Public Health Commission, which continues to urge residents to get vaccinated as a protective measure.
Data posted Tuesday to the commission’s website show the seven-day positive test average through Sunday was 100.7 per day, or 14.8 per 100,000 residents.
“Our goal is to be at 67.9 positive tests or less per day (10 cases per 100K residents),” the site says. “Our threshold for concern is 339.7 positive tests per day (50 cases per 100K residents).”
The waste water data comes as a new coronavirus variant named XBB has swiftly become the dominant form of COVID-19 spreading in the Northeast, jumping from about 35 percent of cases during the week ending Dec. 17 to just over half last week, according to CDC data.
Previous Globe material was used in this report.