A California hospital is investigating whether an employee might have unintentionally spread COVID-19 to dozens of their colleagues by wearing an inflatable Christmas costume.

A Kaiser Permanente employee died and dozens of workers were infected with the coronavirus after a staffer appeared at one of its Northern California medical centers wearing an inflatable holiday costume on Christmas Day, the hospital and health care company said Monday.

Kaiser Permanente San Jose Medical Center confirmed that 44 employees in its emergency department have tested positive since Dec. 27 and that one of those staffers has died of COVID-19 complications. Out of respect for the employee's privacy and family, the hospital did not identify them. 

The Oakland-based hospital chain is investigating the outbreak and says the source could be a blow-up, holiday costume worn by a staffer who “briefly” visited the department Dec. 25, according to its statement.

The brief appearance was not sanctioned by the hospital, officials said.

Hospital officials are reportedly investigating whether the inflatable nature of the costume might have caused greater spread of infectious particles. Such costumes use a battery-powered air-circulation machine, and COVID-19 is primarily spread through exposure to respiratory droplets carrying the virus, according to the Centers for Disease Control and Prevention.

Irene Chavez, senior vice president and area manager at Kaiser Permanente San Jose Medical Center, said in a statement: "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."

No patients are believed to have been infected in the department on Christmas Day, but officials say they’re continuing to conduct additional tests. Employees who have confirmed or suspected cases are isolating at home, and the hospital has performed deep cleanings, officials said.

The harrowing incident comes at a time when Santa Clara County, where San Jose is located, is plagued by a significant wave of coronavirus cases. As of Monday, the county had 691 people hospitalized with COVID-19 and 91% of its ICU beds filled, according to its Emergency Operations Center. 

Santa Clara has recorded more than 74,000 cases and 747 deaths since the start of the pandemic.

The Associated Press contributed to this report.