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ORINDA — In the largest outbreak so far among Bay Area nursing homes, at least 27 people have tested positive for coronavirus at a skilled nursing facility in Orinda, health officials confirmed Friday.

That’s more than half of the residents who live at the Orinda Care Center, a short-term rehabilitation and long-term care facility for older people with about 47 beds. After two staff members sought medical care for coronavirus symptoms early this week, Contra Costa County health officials began investigating Tuesday and found out late Wednesday that those workers and two residents of the facility had tested positive for the illness.

Further testing of all others in the facility found that 24 residents and three staff members were positive as of Friday, said Barbara Lillemon of ReNew Health, a management company that consults with the Orinda Care Center. Contra Costa County health officials are still awaiting a handful of test results but said 14 people at the facility have tested negative so far. Lillemon said Friday that two residents were taken to a hospital while the other 22 residents remained at the center in isolation. More than half of the people infected are older than age 80, said Contra Costa County health officer Dr. Chris Farnitano.

“It’s a virus without a vaccine. It’s a virus without a medical cure. Doctors are finding out more and more every day, but we’re not there yet,” Farnitano said. “So yes, we’re very concerned … especially for the elderly.”

But, he added, it did not come as a surprise; health officials have been preparing for outbreaks at nursing facilities. Besides those hospitalized, residents and staff are staying put at the Orinda center. Asymptomatic staff who tested positive are caring for the infected residents, and staff who tested negative are separately treating residents who also tested negative.

“So if we move people, we create an opportunity for the virus to spread from one family unit — one household to another,” said Dan Peddycord, Contra Costa’s public health director.

The facility had also taken steps to cancel group activities or meals and ban visitors except in extreme cases. From outside the Orinda Care Center on Friday afternoon, the turmoil inside was all but invisible. The large two-story facility offers views of the bucolic green hills of Orinda, across the street from a school district building and a park with softball and soccer fields where a few people were walking around. The only hint was a small sign taped to the front door, which read: “To safeguard the residents of this facility it is now closed to visitors until further notice.”

When a man passing by with two children asked a photographer what was happening and was told about the number of infected patients, the three ran across the street. Another man pulled up in a truck and said he was there to inspect the facility’s fire safety systems.

“Well I’m not going in there now,” he said when told about the outbreak.

It’s the largest known nursing home outbreak in the Bay Area, but far from the only one. Public health workers for the county are also now in the early stages of investigating and testing at two other senior care facilities in the county, Farnitano said.

At San Jose’s Canyon Springs Post-Acute Care center, 26 residents and staff are being monitored for COVID-19, including 11 people who had tested positive as of Friday. Seniors and people with underlying medical conditions, like many of those who receive care and treatment at senior centers and skilled nursing facilities, have had the highest mortality rate from the virus.

It was at a nursing home in Kirkland, Washington, that the first outbreak in the United States exploded. Eighty of its 120 residents tested positive, and more than 30 died from the virus. In the Bay Area, smaller outbreaks have spread across nursing and senior care homes, but none as large as that at a Yucaipa nursing home in San Bernardino County, where 51 residents and six staff tested positive for COVID-19 and two residents died, health officials said Tuesday.

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Coronavirus rates soar in college towns as students return to campus At a news conference Friday, Farnitano urged people to cover their faces with masks or coverings such as bandanas if they have to leave their homes and be around others.

“The situation is very serious, and we are deeply concerned about residents of our senior care facilities in Contra Costa County,” Farnitano said. “That is why we need everyone to follow the stay-at-home order, social distancing guidance and other measures in recent health orders — to protect the people in our community who are vulnerable to severe illness from COVID-19.”

Please help us shed light on senior care by emailing us at seniorcareinquiries@bayareanewsgroup.com. Your information will reach reporters who are covering the impact coronavirus is having on nursing homes and assisted living facilities. You can also leave a phone message at 510-208-6458. Thank you for your help.