New data shed more light on source of coronavirus clusters around Mass.

A testing site set up by Harvard Street Neighborhood Health Center at Prince Hall Grand Lodge in Boston this summer.Jessica Rinaldi/Globe Staff

Amid a surge of coronavirus cases in Massachusetts, new state data indicate that dozens of clusters in the past month have been identified in child care settings, nursing homes, senior living centers, restaurants and food courts, and from organized athletic activities.

Yet many of these clusters — identified as two or more confirmed cases with a common exposure — resulted in a relatively small percentage of the roughly 20,000 new confirmed cases for that period. By far the largest number of clusters counted by Massachusetts are from households, defined as a shared residence of people who are not identified with another cluster. And contact tracers were not necessarily able to learn whether those infections were linked to workplaces, social gatherings or other activities.

Of the 28 COVID-19 clusters linked to child care from Sept. 27 through Oct. 24, just 70 confirmed infections were identified, along with 253 close contacts that required additional tracing and testing.

Similarly, just 70 confirmed cases were identified from 19 clusters in restaurants and food courts, the data show.

In posting the new data, Massachusetts joins a handful of other states that are sharing such information.

Health departments in some states, including Louisiana, post reports from their contact-tracing programs that specify the businesses, schools, or other facilities where outbreaks are occurring. Others, such as Vermont and Colorado, post the occupations, industries, or settings — such as bars, casinos, or food processing plants — with the highest number or percentages of infections in their states.

Massachusetts’ new data show 2,707 clusters involving 6,830 new cases linked to households. That accounts for about a third of all the new infections in the past month.

“A large amount of transmission is occurring in households, a place where people let their guard down and feel safe,'' said Tory Mazzola, a spokesman for the state’s coronavirus command center. ''It’s critical that residents are aware of this and — especially those living in multi-generational homes or with family members who have underlying conditions — take precautions even in their home, such as wearing a mask, washing hands and not sharing utensils, as a few examples.”

Carlene Pavlos, executive director of the Massachusetts Public Health Association, said the household data leaves too many unanswered questions.

“What we really want to understand is how is the spread getting into the community," she said. “Residents living in the same household, we know they are likely to spread it to each other."

Earlier this week, Governor Charlie Baker said workplace infections are not driving the state’s surge in cases, but the new data suggests that’s an open question.

The data do not identify whether the cases and clusters identified in nursing homes, hospitals, and other health care settings are among workers or patients. But it does show that about 16 percent of the confirmed cases linked to clusters in the past month are from various sites, including health care, restaurants, retail stores, and other settings.

As the holidays approach, Baker has urged residents to be cautious about social gatherings, but the new data suggest those gatherings are not necessarily fueling the latest surge in coronavirus infections.

The new numbers show 11 new clusters traced to social gatherings in the last month. Yet those clusters accounted for just 67 new confirmed cases, along with 50 other people considered close contacts who may have been infected.

“Clearly that is not what is driving this latest spike of over 1,000 new cases a day,” Pavlos said.