Laguna Honda Hospital, the city-owned facility that is a permanent home to hundreds of elderly patients, is placing two units under quarantine and locking down the entire facility for residents as of 5 p.m. Wednesday in order to contain a possible coronavirus outbreak.

The move comes as five staff members at the facility tested positive for COVID-19 — and before any of the campus's 750 residents have turned up positive. The Chronicle reports that only 15 residents have been tested so far, and all those tests have come back negative.

Nursing homes in the Bay Area and in Washington State have become vectors for the disease, leading to multiple deaths among closely quartered, elderly residents with underlying health conditions. Last week we learned of three residents at a Burlingame facility, Atria Senior Living, who had tested positive for COVID-19 after showing symptoms, and subsequently two more residents fell ill. Of the five, two have already died and the others remain hospitalized.

Per the Chronicle, Laguna Honda will fully quarantine two units, South Five and South Four, where the infected staff members worked. Meanwhile, after 5 p.m., residents at the entire facility will no longer be able to go in and out, but they will be able to use the outdoor spaces on the 62-acre campus. Visitors and other guests have been shut out of the facility since March 6.

The infected staff are described as four nurses and one worker in the Environmental Services unit. As of this morning, as KTVU reported, two staff members had tested positive.

It's not clear if there is a plan to test more Laguna Honda residents, like those who might have had contact with the infected nurses, but that may be underway.

Meanwhile, as the Chronicle reports, UCSF has opened its own mobile testing site for its 12,000 employees.