A northern California person has contracted the coronavirus without traveling outside the United States or coming in contact with another patient known to have the infection, the first sign that the disease may be spreading within a local community, the Centers for Disease Control and Prevention reported Wednesday night.

How the person acquired the respiratory disease is unknown.

"It's possible this could be an instance of community spread of covid-19, which would be the first time this has happened in the United States," the CDC said in a statement, referring to the disease caused by the coronavirus. The health agency left open the possibility, however, "that the patient may have been exposed to a returned traveler who was infected."

Community spread would represent a significant turn for the worse in the battle against the virus. To date, the United States has 60 known cases of the infection, with 59 among people who traveled to Asia or were spouses of people who went there. The majority, 42, picked up the virus while quarantined on the Diamond Princess cruise ship off Japan.

The CDC said the case "was detected through the U.S. public health system — picked up by astute clinicians." The agency said only that the person lived in California. The Washington Post confirmed that he or she is in the northern part of the state.

Little else was known about the patient — including gender.

The virus, which originated in Wuhan, China, has killed 2,772 people and sickened more than 81,000 as it has spread around the globe, reaching every continent except Antarctica. The CDC on Tuesday warned Americans that community spread is almost certain to occur, and to prepare for significant disruption in their daily lives.

President Donald Trump on Wednesday evening appointed Vice President Mike Pence as the new head of the task force coordinating the battle against the virus.