THE NUMBER of communities at high risk for COVID-19 nearly doubled on Thursday even with a new set of metrics sharply raising the threshold for attaining that designation.

The new metrics were implemented last week and caused the number of high-risk, or red, communities to drop from 121 to 16. But the number rebounded this week to 30 as rising case counts began to overwhelm some communities.

Norfolk, which reported 48 cases per 100,000 people last week, saw the number increase to 145.8 this week, largely because of an outbreak at a state prison there. Its positive test rate (positive tests divided by total tests) rose to 11.6 percent.

Lawrence appears unable to contain the virus. Cases continued their steady rise, jumping from 62.4 cases per 100,000 people last week to 82.6 cases this week. Lawrence’s positive test rate was 11.78 percent.

Other communities with the highest rates were Marion (66.8 cases per 100,000 people), Fall River (62.5 cases per 100,000), Chelsea (57.8), Tisbury (51.3), Fitchburg (48.5), Everett (47.7), Revere (47.7), and Somerset (47.1).

The statewide rate continued to rise, going from 15.3 cases per 100,000 people last week to 20.7 cases this week. The state also hit a grim milestone on Thursday, as 21 new deaths from COVID-19 raised the total so far to 10,015. There were 2,485 new positive cases reported Thursday.

The new metrics the Baker administration began using last week break communities into three groups based on population size and measure risks based on different metrics – the number of overall cases in smaller communities and a combination of cases per 100,000 people and the positive test rate in larger ones.

The previous metric was a one-size-fits-all approach that used cases per 100,000 people over the previous two weeks. Under the new metrics, the new starting point for designation as a red community was raised from 8 to 10.

The Baker administration’s color-coded COVID-19 map – red for high-risk communities, yellow for moderate-risk communities, and green and gray for low-risk communities – has become a yardstick for municipalities to see how they are doing, whether they should slow down the reopening process, and whether schools should use some form of in-person learning.

When Gov. Charlie Baker unveiled the new metrics last week, he said school districts should shift to in-person learning even if they are designated red as long as there is no sign of spread at the community’s schools.

The Department of Elementary and Secondary Education released data Thursday showing the number of COVID-19 cases at K-12 schools hit 191 for the period from November 5 through November 11, up from 154 the previous week. Staff cases during that time period rose from 98 to 157.

There are approximately 450,000 students in the state’s schools and 75,000 staff. The case numbers are from schools with students learning in-person or using a hybrid model, which was about 77 percent of districts as of last Friday.

For the first time, one district had student cases in the double digits – Woburn with 12. Students tested positive in 82 school districts.