Cambridge City Hall, where on Monday the city manager praised cautious coronavirus policies as keeping the city in a positive “green” rating on new cases. (Photo: Marc Levy)

Top city officials boasted on Monday that their cautious policies and extensive testing meant that Cambridge had stayed in the low, “green” category for a minimal rate of new Covid-19 cases, while other large cities were yellow and red. Four days later the city has became a “yellow” community, reflecting a rise in new infections.

Cambridge reported an average of 4.1 new confirmed cases per 100,000 population over the previous two weeks, the state Department of Public Health said in a weekly report Thursday. That put the city just over the line for a moderate risk, or yellow, community, which starts at four new cases per 100,000. In the previous week, Cambridge’s rate was 3.3 new cases per 100,000.

Update on Oct. 29, 2020: A week later, the city was back in the green category, if barely: Its rate was 3.9 new cases per 100,000 population, the state reported.

The state may have taken some of the sting out of the yellow designation by noting that Cambridge is also a city where at least 30 percent of new cases in the past two weeks came from certain “high-risk settings” such as universities, nursing homes and group homes, the city said in its daily update Thursday.

City Manager Louis A. DePasquale told city councillors Monday that precautions such as canceling city-sponsored Halloween celebrations, while “a difficult decision for us to recommend,” had helped do the trick in controlling new cases. “This recommendation is in line with the conservative approach that we have been taking with our public health strategies, and I believe this approach has played a significant role in Cambridge rating still as a green community,” DePasquale said.

Chief Public Health Officer Claude Jacob said more than 60 cities and towns in Massachusetts are in the red category, at eight or more cases per 100,000, but “we’re still holding steady in the green level.”

Causes for concern

The rate of new cases in Cambridge has been rising steadily. It was 2.4 cases per 100,000 two weeks ago and two cases per 100,000 at the beginning of September. While city officials praised their policies at the council’s Monday meeting, two councillors said videos showed flagrant and open violations of orders mandating masks and recommending social distancing. One depicted a large crowd of college-age people with no masks outside a Harvard Square restaurant. The other showed a “party bus” picking up young people, also maskless, along with alcoholic beverages, at Cambridge Crossing.

DePasquale, who got copies of the videos from councillors Marc McGovern and E. Denise Simmons, vowed to step up enforcement of the requirements.

After hearing news of Cambridge entering the yellow category, two other councillors, vice mayor Alanna Mallon and Quinton Zondervan, tweeted advice to residents to wear masks, practice social distancing and wash their hands.

In another Covid-19 development Thursday, Cambridge Rehabilitation & Nursing Center, one of the city’s three nursing homes, reported that one to four workers had tested positive for the virus on Monday. The information was on a state website for self-reported data from long-term care facilities.