The firefighters from Engine Company 20 in Irvine were exposed to the patient on Saturday night after responding to a medical call, according to an Orange County Fire Authority spokeswoman.
The firefighters were told by dispatch that the patient showed signs of coronavirus.
The patient had a history of international travel and was transported to a local hospital.
The fire station was later disinfected and the firefighters were in isolation until test results come back Monday evening.
It's unclear how many firefighters were under isolation.
A spokesperson for OCFA said the isolation took place under an abundance of caution.
The decision to isolate the firefighters was not a directive from Orange County Healthcare Agency. The firefighters were involved in making the decision.
The isolation came amid the Orange County Board of Supervisors holding an emergency meeting Monday morning to ratify a local health emergency declaration in response to the novel coronavirus.
The declaration, which will remain in effect for 30 days, will allow the county to request mutual aid from local and federal government agencies should the county exhaust all of its resources, officials said.
Officials were expected to discuss a plan to train first responders and medical providers on how to recognize and treat COVID-19 patients in the event of a local outbreak.
Testing for the virus is currently underway across the county. Public health officials want anybody experiencing flu-like symptoms, who have come in contact with others who may be infected or who have traveled to affected areas across the globe, to get tested.
We’re now able to test individuals that meet @CDCgov criteria for #COVID19 testing at our Public Health Lab, including: (1) persons with fever or lower respiratory illness who had close contact with a COVID-19 patient within 14 days of symptom onset...— Health Care Agency (@ochealth) March 1, 2020
Costa Mesa and county officials had been geared for a hearing in federal court Monday for a temporary restraining order to block plans to house 30 to 50 infected coronavirus patients at Fairview Developmental Center despite the fact that federal authorities withdrew their request to use the site after receiving pushback from the county leaders and residents.
Federal government drops plans to use Costa Mesa facility as coronavirus quarantine site
"I think the fact that we succeeded in pushing back on Fairview being a repository of COVID-19 patients doesn't mean we're in the clear as a county," Orange County Supervisor Andrew Do said. "We have been given warning by the CDC and World Health Organization today that this pandemic may be severe, so it is time for us to look internally and make sure we have an adequate plan in place. ... We need a game plan and playbook in place so we don't make mistakes."
The scheduled hearing was canceled following the announcement that the site was no longer being considered as a possible quarantine site. And while it was hailed as a victory for the city it did not do much to satisfy officials.
"This is a victory for the citizens of Costa Mesa and Orange County," Mayor Katrina Foley said in a statement. "But the government has not promised not to place future infected persons there, so the battle is not over."
Orange County officials declare local health emergency amid coronavirus concerns
Though the county has only confirmed one case of COVID-19, a patient who officials say has since recovered, a local health emergency was declared last week.
MORE: From hand-washing to wearing masks, here's how to protect yourself from coronavirus
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City News Service contributed to the report.