A Northern California resident may be the first case of “person-to-person transmission” of the novel coronavirus in someone with no known connection to travel abroad or another infected individual, the U.S. Centers for Disease Control and Prevention announced Wednesday.

The person lives in Solano County, northeast of San Francisco, and is getting medical care in Sacramento County, according to the California Department of Public Health. The agency said it’s begun the process of tracking down people who the patient has been in contact with.

The CDC reported the case Wednesday night.

The patient was brought to UC Davis Medical Center from another Northern California hospital on Feb. 19 but it was four days before the CDC heeded a request to test the patient for COVID-19, according to an email sent to employees Wednesday by the hospital’s interim CEO, Brad Simmons, and David Lubarsky, CEO of UC Davis Health.

The patient arrived on a ventilator and special protection orders were issued “because of an undiagnosed and suspected viral condition,” according to the email, which was sent to employees.

The hospital asked the CDC to test for the coronavirus but testing was delayed until Sunday “since the patient did not fit the existing CDC criteria for COVID-19,” the email said.

The hospital, which has treated other coronavirus patients, has been taking infection prevention precautions since the patient arrived. The email said officials believe there was only a small chance that others at the facility were exposed to the virus.

“Nevertheless, a small number of medical center employees have been asked to stay home and monitor their temperatures,” the email said.

Messages to the CDC seeking comment on the email were not immediately returned Wednesday night.

The patient had no known travel to a country where a virus outbreak has been taking place, or connection to a known patient. But it’s possible they were exposed to a returned traveler who was infected, the CDC said.

All of the 59 other cases in the U.S. had traveled from abroad or had been in close contact with those who traveled.

The risk to the general public is low, the state health department stressed, describing California’s health care system as strong.

Lawrence Gostin, director of the World Health Organization Collaborating Center on National and Global Health Law, said the new case is “the first signal that we could be having silent transmission in the community,” according to the Los Angeles Times.

“It probably means there are many more cases out there, and it probably means this individual has infected others, and now it’s a race to try to find out who that person has infected,” Gostin said.

The announcement came after President Donald Trump announced that Vice President Mike Pence would lead the White House’s efforts on the disease.

Trump said the country is “very, very ready” for the potential threat.

Earlier U.S. cases included 14 in people who traveled back from outbreak areas in China, or their spouses; three people who were evacuated from the central China city of Wuhan; and 42 American passengers on the Diamond Princess cruise ship who were evacuated by the federal government to the U.S. from where the ship was docked in Japan.

Some of those evacuated were taken to Travis Air Force Base, which is in Solano County. A number of the earlier cases have been in California, including among some of the people taken to Travis and one in which a traveler who returned to San Benito County spread it to a spouse.

California officials have been preparing for the possibility that community spread of the virus might first surface there.

“We have been anticipating the potential for such a case in the U.S., and given our close familial, social and business relationships with China, it is not unexpected that the first case in the U.S. would be in California,” said Dr. Sonia Angell, Director of the California Department of Public Health and State Public Health Officer, in a statement.

The outbreak, which began in China, has infected tends of thousands of people in more than three dozen countries, with the vast majority in mainland China.

The new virus is a member of the coronavirus family that can cause colds or more serious illnesses such as SARS and MERS.

The virus can cause fever, coughing, wheezing and pneumonia. Health officials think it spreads mainly from droplets when an infected person coughs or sneezes, similar to how the flu spreads.

Officials are advising people to take steps to avoid infection with coronavirus or other respiratory infections like a cold or the flu, including washing hands with soap and water and avoiding close contact with people who are sick.