Dozens of health workers in Solano County, Calif., are under isolation and some will be quarantined after being exposed to a patient who recently tested positive for the coronavirus, officials said Thursday.

The patient, who has not been publicly identified, is the first known person to contract the illness without traveling abroad or coming into close contact with an infected individual. She visited health centers, potentially exposing a number of workers at two hospitals -- NorthBay VacaValley Hospital in Vacaville and the UC Davis Medical Center in Sacramento, according to officials.

They didn't say how many workers were impacted but said it was under 100 people.

“There were multiple health care personnel who were exposed to the individual," Dr. Bela Matyas, the county public health officer, said at a news conference Thursday. “At both hospitals we are at present aggressively evaluating everyone who may have had contact with this patient. They are being identified and their risk for exposure is being assessed.”

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Efforts are being made to identify all the workers who may have been exposed. A spokesman for NorthBay Health Care said the number of health care workers impacted was "a moving target."

The announcement comes hours after county health officials declared a local emergency and activated its Department Operations Center to identify and screen those potentially exposed to the coronavirus, known as COVID-19.

Officials called the virus a public health threat but cautioned that the risk to the public in Solano County remains low.

"The ability for us to address this exists," Matyas said. "I think that we can weather this just as we have weathered other similar events in the past."

The patient was brought to the NorthBay VacaValley Hospital earlier this month with flu-like symptoms and stayed for three days. She didn't fit the federal health criteria to be tested for the virus, officials said Thursday.

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She was later transferred to UC Davis Medical Center where she was administered a test at the request of the U.S. Centers for Disease Control and Prevention (CDC) and was found to have contracted the coronavirus.

Doctors at the hospital asked the CDC to test the woman on Feb. 19 but were not given approval until Sunday.

Meanwhile, at the University of California campus in Davis, three students who live together in a dormitory hall are being monitored for potential infection, the university said. One student showed signs of the virus and was removed from the campus.

"As an additional precautionary measure, daily disinfection practices are being implemented within all Student Housing and Dining Services properties," the school said in a statement.

Additionally, students seeking care at the school's wellness center are being asked about recent travel and contact with anyone possibly infected.

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California Gov. Gavin Newsom said Thursday that more than 8,000 California residents were being monitored for the virus.

Some 82,000 people have been sicked by the coronavirus worldwide and more than 2,700 have died. Most of the cases are in China where the virus was first reported and has prompted tough measures to keep it from spreading.

The Associated Press contributed to this report.