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 at a hospital in San Jose, California, 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.

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. Some costumes cover the wearer's face, while others leave it exposed.

Chavez declined to say what kind of air-powered costume the hospital employee wore, but she described it as "holiday themed." As part of its response to the outbreak, she said, the hospital was looking into "whether the costume, which did have a fan, was a contributing factor." Air-powered costumes have been banned, she said.

It was unclear how long the employee had worn the costume in the emergency department. The hospital declined to say whether any patients had been infected.

It was also unclear whether any of the infected staff members had received the first dose of a COVID-19 vaccine, but experts have said that it takes at least a couple of weeks for the vaccine's protective effects to kick in. According to the hospital, 40,000 Kaiser employees in Northern California have received the first dose of the vaccine.

"Any exposure, if it occurred, would have been completely innocent, and quite accidental, as the individual had no COVID symptoms and only sought to lift the spirits of those around them during what is a very stressful time," Chavez said of the costumed worker.

The emergency department will be deep-cleaned, Chavez said, and in addition to protocols that were already in place, employees will be offered free weekly testing.

According to the Centers for Disease Control and Prevention, the coronavirus is primarily spread through respiratory droplets and can "sometimes be spread by airborne transmission" of both larger droplets and smaller aerosols when people "cough, sneeze, sing, talk or breathe."

Dr. Jose-Luis Jimenez, an aerosol expert and a professor of chemistry at the University of Colorado Boulder, helped investigate the choir outbreak in Skagit County, in which at least 53 infections and two deaths were traced to a singing practice in Washington state. In an interview Sunday, he said the outbreak among the staff at Kaiser Permanente San Jose Medical Center was most likely the result of airborne transmission.

"It's kind of like the choir case," Jiminez said. "There is no way to infect 43 people when you're wearing a costume other than through airborne transmission, through aerosols, because you're inside a costume and cannot touch objects or get people infected through surfaces."

The hospital is in Santa Clara County, where there have been 73,493 confirmed coronavirus cases, according to a New York Times database. There have been 2,397,923 confirmed cases across California.

More than 21,000 people were hospitalized in California on Jan. 1, according to the Times database, a 26% increase from two weeks earlier.