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SAN JOSE — Four San Jose firefighters have tested positive for the coronavirus, and the impact of the disease on the fire department could grow in the coming days with more awaiting tests and the revelation that family members of the ill firefighters have also been infected, officials said.

As it stood Thursday afternoon, city officials reported that 80 firefighters may have been exposed to COVID-19, meaning that more than 10 percent of the city’s 750-member firefighting staff was affected. The city said 16 are back on duty, and that 52 remain on leave and in quarantine. The firefighters union said that of those in quarantine, two firefighters are showing symptoms of the virus and were awaiting test results.

The Santa Clara County Health Department announced late Thursday afternoon that the number of people who have tested positive for the potentially fatal disease had increased from 48 to 66.

The head of the firefighters union said some – he didn’t specify how many – family members of firefighters have also tested positive for the virus.

“As firefighters, we commit our careers and lives to serving the public in their time of need. Responding to the COVID-19 pandemic as it grows among our residents is an unprecedented challenge, and we are up to that challenge,” Sean Kaldor, union president of the San Jose Fire Fighters IAFF Local 230 said in a statement. “But it is also taking a tremendous toll on us as we fall ill and support our ill family members.”

Assistant Chief Reginald Williams said Thursday it was unclear how the infected firefighters were exposed the virus, and a news release from the firefighters union did not specify whether the firefighters contracted it from each other, from relatives, or from the community.

The city has deep-cleaned Fire Station 9, at 3410 Ross Ave., and

Fire Station 31, at 3100 Ruby Ave., as well as the fire training center at 255 South Montgomery St., according to Rosario Neaves, a spokeswoman for the mayor’s office. That’s where the firefighters were either assigned or came into contact with others, she said.

“Because our firefighters work in teams and they train together, and they eat together and they sleep in the same areas, they are at risk for possible exposure,” Williams said at a Thursday morning news conference.

Kaldor said the department is trying to address the fact firefighters work and live close to one another, making it difficult to achieve the “social distancing” experts recommend to try to avoid contracting the disease.

In the field, Kaldor said that includes new protocols including initially sending just one firefighter into a home or dwelling to assess a medical call and assess a patient’s stability, to avoid unnecessary exposure.

“Even though we’re being asked to respond to someone who twisted their ankle, because now we realize we get there, and 10 minutes into being on scene, they say, ‘Well actually, I’ve kind of had a fever and have been weak the past two days,’ and you’ve been exposed,” Kaldor said.

Thursday morning, when the fire department announced that the first firefighter had tested positive for COVID-19, Williams said that firefighter was “in a hospital in another city where he resides, being treated by medical professionals.”

Hours later, the city announced three more firefighters had tested positive for COVID-19.

Identities and cities of residence for the firefighters have not been publicly released in accordance with medical privacy laws.

Mayor Sam Liccardo said that the firefighter exposures happened several days ago, so he “expects we’ll be seeing many people move off of self-quarantine soon” who test negative and don’t exhibit any symptoms.

“What we want to do first is to notify those individuals who were treated by a firefighter who tested positive and we’re currently doing that in concert with the county,” Liccardo said. “I would not be surprised if the number of firefighters who test positive grew, but the good news is those people are already on quarantine and not in a station. City staff have been very proactive of identifying those people who might be potentially infected.”

Williams said fire stations in the city will be fully staffed despite having about a tenth of its workforce under quarantine, with those vacant shifts being filled primarily in the form of overtime by summoning off-duty personnel to work.

He added that fire station visits by the public, as well as educational and fire-safety outreach programs have been suspended until further notice.

Kaldor said firefighters, as medical first-responders, “encounter infectious diseases on a daily basis,” and are well-versed in decontamination practices.

“COVID-19 is the latest in a series of threats to the public and our firefighters. We are working closely with the department, county EMS,and county Public Health to ensure best practices are followed to minimize transmission of this

virus as the pandemic crosses San Jose,” he said. “As firefighters, we are also have a close bond to each other, supporting those of us who have become ill, and their families, in this time of heightened need.”

Staff writers Maggie Angst and Jason Green contributed to this report.