The Sonoma County resident had traveled recently on a international cruise ship that departed from San Francisco to Mexico and has been in the county for 10 days since return, according to health officials.
The patient has shown symptoms of the virus and is currently in stable condition in an isolation room at a local hospital in an unknown location.
The Centers for Disease Control and Prevention (CDC) will conduct another test to confirm the diagnosis of the resident.
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This is the second case of COVID-19 in the Sonoma County, according to health officials.
Another person with the coronavirus was transferred to Sonoma County from a quarantine at Travis Air Force Base.
That individual is not a resident of Sonoma County, officials said.
In a press conference Monday afternoon, health and county officials reminded residents to be vigilant with personal hygiene and to wear a face mask only if you are ill.
Health officials ask that healthy people refrain from wearing face masks.
The news out of Sonoma County comes after two more cases were confirmed in Santa Clara County and one with a presumptive positive test in San Mateo County.
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Both of the new cases in Santa Clara County are males and had household contact with other patients confirmed to have coronavirus, county officials said. They are both now under home isolation. There are now nine confirmed novel coronavirus cases in the county.
San Mateo County's case is an adult who is currently in isolation at the hospital. The case is pending confirmatory testing by the Centers for Disease Control and Prevention. The patient has no known exposure to the virus through travel or through contact with a confirmed case of COVID-19. The source of exposure is unknown at this time.
With this new case, it brings the total positive COVID-19 cases in San Mateo County to two. The previous case is an individual who was returned to the U.S. by the CDC. The patient is currently in isolation and in good condition.
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