WASHINGTON — A person in Northern California 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 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. The health agency left open the possibility “that the patient may have been exposed to a returned traveler who was infected.”

The state of California, however, called the case its first instance of community transmission.

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 vast majority, 42, picked up the virus while quarantined on the Diamond Princess cruise ship off Japan.

If the infection is confirmed to be a case of “community spread,” said Jennifer Nuzzo, epidemiologist and senior scholar at the Johns Hopkins Center for Health Security, “it would confirm what we have long suspected — that there is a good chance there already are people infected in this country and that the virus is circulating undetected. It points to the need for expanded surveillance so we know how many more are out there and how to respond.”

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.

Las autoridades creen que la propagación del coronavirus es probable. (Agencia de Protección de la Salud) 1585620 1585620
California coronavirus patient wasn't tested for days

The individual is a resident of Solano County, according to the California Department of Public Health. The patient is being treated at UC Davis Medical Center, according to a person familiar with the case who spoke on the condition of anonymity because the details are not public.

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Solano County is home to Travis Air Force Base, where hundreds of Americans repatriated from China, and others brought home from the Diamond Princess Cruise ship have been kept in quarantine. Many of them have been released.

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The health department said it has already begun tracing people who may have come in contact with the individual.

“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 Sonia Angell, director of the California Department of Public Health and State Public Health Officer.

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.