Solano County, Calif., Health Officer Bela T. Matyas said Thursday that officials still did not know how a county woman — the first person in the United States to develop the new coronavirus with no travel or connection to individuals who visited affected countries — had acquired the illness.

The person was not connected to the repatriated evacuees at nearby Travis Air Force Base, he said.

“This individual has no connection whatsoever to that federal mission and to any of the personnel that have been involved in that evacuation process. This does appear to be a person who genuinely did acquire [the] illness in our community.”

Matyas said that because the patient was not a known coronavirus victim, she was not placed in isolation at the hospital upon their arrival, meaning dozens of workers could have potentially been exposed. Dozens of hospital workers, but fewer than 100, were being assessed, officials said.

“Some of them will be under isolation, some of them under quarantine,” Matyas said, adding that others were low-risk. “The hospitals are working aggressively to identify properly the individuals from those environments.”

Meanwhile, Matyas said, the community-acquired case meant the disease had arrived in the county, meaning officials would have to shift from a containment to “mitigation” approach — essentially minimizing the risk of transmission.

Containment, he said, is only possible when health-care personnel know the identity of everyone who is sick. He declined to disclose biographical details about the patient or where she worked.

He said the woman’s family would remain in quarantine for 14 days.