VACAVILLE, Calif. • Public health officials were retracing the steps of a Northern California woman on Thursday believed to be the first person in the U.S. to contract the highly contagious coronavirus without traveling internationally or in close contact with anyone who had.

The diagnosis, confirmed Wednesday, marks an escalation of the worldwide outbreak in the U.S. because it means the virus could now spread beyond the reach of quarantines and other preventative measures. But state health officials were quick to reassure the public Thursday that such a scenario was inevitable and the risk of widespread transmission remained low.

Doctors at the UC Davis Medical Center said they asked the U.S. Centers for Disease Control and Prevention to test the woman for the virus after she was admitted on Feb. 19. But they said the CDC did not approve the testing until Sunday “since the patient did not fit the existing CDC criteria” for the virus, according to a memo posted to the hospital’s website.

CDC spokesman Richard Quartarone said the agency is concerned about reports that the CDC delayed testing the woman. He said the agency is investigating, but a preliminary review of CDC records indicates the agency did not know about the woman until Sunday, the same day the woman was first tested.

The CDC can test about 400 specimens per day, Quartarone said.

California Gov. Gavin Newsom said the state was limited in how many people it could test because it only had 200 testing kits. But he said federal officials have promised to send many more testing kits in the coming days.

“Everybody in this country is rightfully anxious about this moment,” Newsom said. “I think they should know we are meeting this moment with the kind of urgency that is necessary, and I don’t want to over extend the anxiety.”

Investigators were focused Thursday on tracing the woman’s movements to figure out how she got the virus and who else she may have unwittingly infected. The woman first sought treatment at NorthBay VacaValley Hospital in Vacaville, a city of more than 100,000 people about 60 miles from San Francisco.

Ten experts from the CDC arrived Thursday morning and were heading to Vacaville to help with the search, said Dr. James Watt, interim state epidemiologist at the California Department of Public Health.

With the patient as ground zero, they are interviewing immediate family members.

Some of those people have been treated at Travis Air Force Base, in Solano County where the Northern California woman lives. But there is no evidence the woman has any connection to the base, said Sonia Angell, director of the California Department of Public Health.

Florida Gov. Ron DeSantis speaks Thursday as Deputy Secretary for Health Dr. Shamarial Roberson, left, Florida Surgeon General Dr. Scott Rivkees, second from left, and Lt. Gov. Jeanette Nuñez listen in Tallahassee, Fla. DeSantis attempted to reassure his state that health officials were prepared for any cases of a new virus.

the associated press