Nearly 100 residents had to be removed from a nursing home facility in Southern California on Wednesday after a large portion of its staff stopped showing up for work.

The Magnolia Rehabilitation and Nursing Center in Riverside has 39 confirmed cases of coronavirus, according to county officials, and for two days in a row, 13 of its employees were no-shows. It’s unclear why, exactly, they went AWOL, but with a deficit of nursing assistants, 40 ambulances had to move patients to other facilities — a process that took several hours.

These kinds of nursing facilities have been hit hard by COVID-19, with the age and health conditions of their residents making them more susceptible to the virus. Across the country, nursing homes have been locked down to visitors, and in many different states, they’ve become hot spots for coronavirus.

“The congregate living facilities do pose a greater risk for COVID-19,” Riverside County public information officer Brooke Federico said to the Los Angeles Times, “because they are groups of people [living] together, and also, unfortunately, people who are at skilled nursing facilities are in a more vulnerable population because they are older and have underlying health conditions.”