REDWOOD CITY (CBS SF) — San Mateo County health officials announced Monday their first case of coronavirus, raising the number of cases of COVID-19 in the Bay Area to a least 26.

San Mateo County Health Officer Dr. Scott Morrow said the patient was in isolation and being treated at a local hospital. The patient has had “no known exposure to the virus through travel or through contact with a confirmed case … the source of exposure is unknown at this time.”

The announcement came less than two hours after Santa Clara County announced two additional cases of the illness. There have been nine cases in Santa Clara County so far.

A new case was also reported in San Mateo County.

All four new cases were awaiting final confirmatory testing by the Centers for Disease Control and Prevention.

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“This new case of a positive case of novel coronavirus has happened in San Mateo County and we share the concerns of the Centers for Disease Control and Prevention that we all need to be prepared for COVID-19 to spread within the United States,” Morrow said. “To prevent any illness, follow CDC guidelines including washing your hands frequently, covering your sneeze, and staying home when sick. Also, please dust off your personal emergency plans to make sure you have proper provisions at your home including water, medications, and food.”

San Mateo officials said they were monitoring any close contact the patient has had with others and ensuring that proper evaluation and care is provided if they become ill.

“The current risk of local transmission remains relativity low but the landscape is likely to change rapidly in the coming days, weeks, and months,” the health department said in a release.

Symptoms of COVID-19 are like the flu, which include fever, cough, and shortness of breath. Symptoms may appear in as few as 2 days or up to 14 days after exposure.

If you are experiencing symptoms of COVID-19 and may have had contact with a person with COVID-19 or recently traveled to countries with apparent community spread, health officials said, call your doctor before seeking medical care so that appropriate precautions can be taken.