An air-powered, inflatable costume, worn by a staff member on Christmas to spread holiday cheer, may be to blame for a coronavirus outbreak that infected dozens of workers in a hospital in San Jose, Calif., a hospital spokeswoman said.

An employee wore the costume “briefly” in the emergency department at Kaiser Permanente San Jose Medical Center, the spokeswoman, Irene Chavez, said in a statement.

The hospital began an investigation after 44 staff members tested positive for the coronavirus between Dec. 27 and Friday, she said.

One staff member who was working in the emergency room on Christmas Day has died from Covid-19 complications, the hospital said in a statement on Monday. While the exact cause of the outbreak is under investigation, the costume is “a likely source,” it said.

Inflatable costumes are usually powered by a battery-operated fan that sucks air into the suit, helping it keep its shape. T. rex and sumo wrestler models are among the more popular.