More than 850 residents and staff in assisted-living facilities in California have tested positive for the coronavirus, according to data released late Monday by the state social services agency.

Among the most severe outbreaks were at Chateau III in Contra Costa County, which has 52 residents and staff with confirmed cases, and Silverado Beverly Place in the Fairfax district of Los Angeles, with 50 residents and staff testing positive for the virus.

This marks the first time that state officials have released data on outbreaks in assisted-living facilities — a broad category of congregate living homes for mostly elderly residents. With aging and frail residents in close quarters, assisted-living homes are particularly vulnerable to the spread of the coronavirus.

Nursing homes, which have residents with more advanced medical needs, have been a locus of outbreaks in the state, with more than 3,500 residents or staff testing positive.

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