Neville Center is one of three nursing homes in Cambridge that have more than 30 residents with infections, according to the state. (Photo: Marc Levy)

One-third of Cambridge nursing home and assisted living residents tested positive for Covid-19 in a second round of testing that began Thursday and extended through the weekend, Chief Public Health Officer Claude Jacob said Tuesday. In the first round, a week ago, 28 percent were infected. The testing was part of a unique surveillance program that was intended to test every resident and worker at the city’s three nursing homes and four assisted living centers, regardless of whether they had symptoms.

The increase in the share of residents with positive tests showed up in Tuesday’s case count in Cambridge: a total of 230 residents in long-term care facilities tested positive, compared with 184 on Monday. Also, for the first time, the city Public Health Department gave a complete picture of deaths from the virus among nursing home and assisted living residents: 23 of the 28 deaths in Cambridge were of residents in long-term care, or 82 percent.

Total Covid-19 cases in the city increased to 608 on Tuesday from 544 on Monday. The number of deaths did not change. Jacob presented the figures on nursing home and assisted living cases to a special meeting of the City Council called to hear reports on the pandemic.

“Some of the trends we’ve seen at first pass are a very high rate of infection, particularly within the skilled nursing facilities,” Jacob said. The testing also showed “a great variation in the results depending on the facilities’ subculture or organizational structure,” he said. “We did notice a higher rate of asymptomatic Covid-positive cases than what was anticipated,” Jacob said, referring to people who were infected but exhibited no signs of illness.

All three nursing homes in Cambridge – the Cambridge Rehabilitation and Nursing Center, Sancta Maria Nursing Facility and Neville Center – have more than 30 residents with infections, the state reported Monday. The city has not identified the nursing homes or assisted living centers with infections. None of the facilities except two assisted living facilities that said they had no residents with infections – The Cambridge Homes and Neville Place – has disclosed how many residents have the virus.

The nursing homes are coping with staff shortages “due to positive [test results] or just fear of exposure,” Jacob said. They are also facing shortages of protective equipment, particularly gowns. “We’ve heard that as a theme with these facilities. But at the end of the day, we’re here to help.”

He said the city had assembled a task force to help nursing homes deal with the outbreaks, including people from Cambridge Health Alliance, fire and police departments, Pro EMS and the Public Health Department. If necessary, Cambridge will seek state help such as from the Medical Reserve Corps and National Guard, he said.

Jacob didn’t offer an explanation of why the proportion of infections among long-term care residents had increased over the week between the two rounds of testing. For employees, the percentage dropped: to 10 percent in the second round from 13 percent in the first round.

About 900 people were tested in the second round, which began Friday, compared with about 1,000 in the first round starting April 9, Jacob said. Approximately 500 people also volunteered to have a finger-stick blood test to identify whether they had antibodies to the virus, Jacob said.