FILE - In this March 13, 2020, file photo, a nurse works in the room of a patient who has tested positive for the COVID-19 coronavirus at the Life Care Center in Kirkland, Wash., near Seattle. Nursing home outbreaks of COVID-19 have raised concern in the U.S. since the incident at Life Care Center. (AP Photo/Ted S. Warren, File)

SEATTLE (AP) — An investigation at a Seattle-area nursing home concluded that symptoms aren’t enough to identify who is infected once the coronavirus enters a long-term care facility.

People without symptoms could have the virus, so it won’t work to simply separate residents with symptoms from others. Investigators found that screening based on symptoms alone may be failing to identify half the people who are infected with COVID-19.

A report released Friday focused on a nursing home in King County, Washington, which health officials thought might become vulnerable after an outbreak at a nearby facility, the Life Care Center nursing home in Kirkland.

It concluded that as soon as there’s a confirmed case, all health care workers should don masks and other protective garments, and residents should be isolated as much as possible.

The report did not identify the nursing home. But if found that of 23 residents who tested positive, only 10 had symptoms on the day they were tested.

The report was by state and local investigators, and scientists at the Centers for Disease Control and Prevention in Atlanta.