An inflatable Christmas costume may have spread coronavirus particles at a California hospital, potentially infecting at least 51 employees

• At least 51 hospital employees at Kaiser Permanente San Jose Medical Center have tested positive for COVID-19 between December 27 to January 5.
• The outbreak occurred after an emergency room employee briefly wore an inflatable costume to work on Christmas.
• The costume's fan may have splayed infectious particles across the emergency department.

A well-meaning gesture at a California hospital may have backfired this Christmas: To celebrate the holiday, an emergency room employee at Kaiser Permanente San Jose briefly wore an inflatable costume to work on December 25. Hospital officials are now looking into whether the costume's fan may have splayed infectious particles across the emergency department.

Since December 25, no fewer than 51 hospital employees have now tested positive for COVID-19, The Mercury News reported on Tuesday, citing data from the Santa Clara County Public Health Department.

"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," Irene Chavez, the hospital's senior vice president, said in a statement to ABC7 News.

"If anything, this should serve as a very real reminder that the virus is widespread, and often without symptoms, and we must all be vigilant," she added.

In a statement on Tuesday, public health officials echoed that sentiment.

"This is a stark reminder that COVID-19 can be so easily transmitted through the air and that even letting your guard down for a moment can have consequences," the Santa Clara health department said.

The coronavirus spreads most commonly through respiratory droplets when a person breathes, speaks, sings, coughs, or sneezes - but research has also shown that tiny virus-laden particles called aerosols can linger in the air for minutes or hours in poorly-ventilated indoor areas.

In closed spaces, fans can blow these infectious particles in the direction of another person. That's why the World Health Organization recommends that table or pedestal fans should be avoided in homes when people outside the immediate family are visiting. The US Centers for Disease Control and Prevention also cautions people not to wear masks with built-in valves or vents, which can similarly expel infectious particles into the surrounding air.

Kaiser Permanente told Business Insider over the weekend that the hospital was undergoing a deep cleaning.

"We are also moving quickly to test all emergency department employees and physicians for COVID-19," Chavez said. "Employees confirmed to have COVID-19 or suspected of having COVID-19 due to symptoms will not come to work."

Some of the hospital's employees got their first dose of the coronavirus vaccine just before Christmas, NBC News reported - but it's too early for any of them to have received the full two-dose regimen. It can also take up to a few weeks after the first shot for the body to develop immunity in the form of antibodies against the virus.

That means there's still a chance of vaccinated employees getting sick. The hospital told ABC7 News that emergency staff "would not be expected to have reached immunity when this exposure occurred."

The outbreak arrived at a time when hospitals across the country are already flooded with COVID-19 patients. In the week leading up to Christmas, nearly one-fifth of US hospitals with intensive care units reported that at least 95% of their ICU beds were full, according to data from the Department of Health and Human Services.

Intensive care units in the San Francisco Bay Area, where the San Jose hospital is located, only had 5.1% capacity as of Saturday.

Chavez told ABC7 News that the hospital was "taking steps to reinforce safety precautions among staff, including physical distancing and no gathering in break rooms, no sharing of food or beverages, and masks at all times."

She added: "Obviously, we will no longer allow air-powered costumes at our facilities."

This article has been updated to include a statement from Kaiser Permanente and reflect the latest number of infected employees.