The cities of Boston and Springfield entered the "Red Zone" on Massachusetts coronavirus tracking map as of Wednesday night, as COVID-19 case rates are starting to rise around the commonwealth.

Those cities are now among the about two dozen communities in Massachusetts to have more than eight cases per 100,000 residents. The state's map, which is updated on Wednesday nights, rates each community on the risk of infection with COVID-19 based on the 2 week average daily case rate.

A number of cities and towns in northeastern Massachusetts have now formed a cluster of red, with with Lowell, Dracut, Methuen, North Andover, Middleton and Haverhill joining Lawrence in the "Red Zone."

Most other zones on the state’s map outside that area haven’t changed very much, says Dr. Christopher Gill, an infectious disease specialist and clinical epidemiologist at Boston University's School of Public Health.

‘That whole area has gone red, or has gone from green to yellow; so that that seems to be a very concerning cluster,” Gill said.

“Maybe more reassuring is that when you look at the overall health impact of the COVID- 19 transmission in Massachusetts in terms of hospitalizations and deaths, that has really not changed in the last week," Gill added. "In fact, it's been pretty stable for a while.”

Last week’s figures showed a total of 98 hospitalizations and 184 deaths over the previous two weeks, and Wednesday’s figures showed 124 hospitalizations and 202 deaths.

Gill said caution is still warranted since there is always a delay between a change in case rates and the numbers of people who become hospitalized or die.

Another notable change in Wednesday’s weekly report was the increase in case rates among the youngest residents. That two-week rate for those 19 and under rose more than for any other age group, increasing by about 16 cases per 100,000. The lowest increase was among people between the ages of 60 and 69, which went up by six cases per 100,000.

Gill said that could suggest that the resumption of public school and higher education in the state has been a major contributor to the uptick in cases.

“These data would suggest that's possibly true,” Gill said. “We don't know whether it's concentrated in the older age group of kids who might be in college or the slightly younger age groups who might be in primary or secondary school. You can't tell that from these data, but they are consistent with the concern that this [increase in cases] may be driven by education and or higher education.”

Gill said the uptick in average case rate overall in Massachusetts, from 4.9 cases per 100,000 to 5.7 per 100,000, bears watching.

“It's an increase — but it went from a relatively low number to a slightly higher, but still rather low number,” Gill said. “So this is not the equivalent of a four alarm fire, but it is certainly reason to be concerned, and it's certainly reason to take action. This is the kind of early warning that we hope for when we have data of this kind, that would allow us to concentrate our resources and try to do some transmission prevention interventions now, before it becomes a crisis down the road.”