SAN FRANCISCO — Even as President Donald Trump sought to reassure the public that the risk of coronavirus in the U.S. remains low, ominous news emerged that could heighten the level of concern.

The Centers for Disease Control and Prevention on Wednesday confirmed an infection in California that would represent the first U.S. person to contract the virus despite not visiting a foreign country recently or coming in contact with an infected patient.

"At this time, the patient’s exposure is unknown,'' the CDC said in a statement. "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. Community spread means spread of an illness for which the source of infection is unknown. It’s also possible, however, that the patient may have been exposed to a returned traveler who was infected.''

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This brings the number of coronavirus cases detected in the U.S. to 15, with 12 of them related to travel and the other two to direct contact with a patient. There are another 42 Americans who tested positive on the Diamond Princess cruise ship that was quarantined in Japan, and three detected in Wuhan, the Chinese city at the epicenter of the global outbreak.

In an evening news conference in which he named Vice President Mike Pence as the point man in the administration's response to the coronavirus, Trump pointed out the relatively small number of U.S. cases of an infection that has sickened more than 82,000 people throughout the world, the vast majority in China.

The global death toll hit 2,801 on Wednesday night.

"Because of all we've done, the risk to the American people remains very low,'' Trump said. "We're ready to adapt and we're ready to do whatever we have to as the disease spreads, if it spreads.''

CDC officials have already said it would. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, warned Tuesday of possible “severe” disruptions to everyday life.

"It's not so much a question of if this will happen anymore but rather a question of exactly when this will happen and how many people in this country will have severe illness," she said.

The new case in California may validate that assessment.

Even before that news broke, officials in two of the state's jurisdictions took action in response to the coronavirus' threat.

San Francisco Mayor London Breed on Tuesday issued an emergency declaration aimed at preparing the city for an outbreak – even though no cases of the virus have been confirmed in the city.

And, on Wednesday, Orange County – which has had one case – declared a local health emergency, though the rationale was different.

“Although there are still zero confirmed cases in San Francisco residents, the global picture is changing rapidly, and we need to step up preparedness,” Breed said. “We see the virus spreading in new parts of the world every day, and we are taking the necessary steps to protect San Franciscans from harm.”

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The declaration raises awareness, mobilizes city resources, accelerates emergency planning and coordinates agencies across the city, Breed said. She said it also allows for future reimbursement by the state and federal governments.

Santa Clara and San Diego counties have issued similar declarations to bolster their preparedness.

Breed emphasized the emergency declaration is aimed at getting services ready in the eventuality the virus reaches the city, whose population is more than 20% Chinese or Chinese American.

“Given the high volume of travel between San Francisco and mainland China, there is a growing likelihood that we will see cases of COVID-19 eventually,” San Francisco Health Officer Tomas Aragon said.

Several hundred miles south, Orange County Supervisors Michelle Steel and Andrew Do said the emergency declaration was a response to the proposal to quarantine coronavirus patients in a local city, which has sparked an uproar.

“The county of Orange continues to support Costa Mesa in opposition of state and federal government’s decision to move COVID-19 patients to the Fairview Center,” Do said.

In New York, Mayor Bill de Blasio had a different issue, saying the CDC has underutilized 1,200 hospital beds in the city that could be provided immediately to anyone who is being tested for coronavirus or who has tested positive.

De Blasio called on the CDC to launch a broad expansion of airport testing that he said was “too narrowly focused” on travelers to the U.S. from China.

“We think that has to be expanded to any traveler coming from a country that has seen a major surge in cases,” de Blasio said, naming Hong Kong, Iran, Italy, Japan, Singapore, South Korea, Taiwan and Thailand.

Jeffrey Goad, a former president of the California Immunization Coalition, notes that the precautions to avoid coronavirus are similar to those for the flu – frequent hand washing, avoiding close contact with the sick and staying home if you are ill.

Fewer than 60 cases of coronavirus have been confirmed in the U.S., most of them repatriated passengers who were on board the Diamond Princess cruise ship that was quarantined in Japan. By contrast, more than 30 million Americans already have suffered from the flu this season. Maybe we should be paying more attention to that, Goad said.

“It’s important to remember that influenza kills thousands of people in the U.S. every year,” said Goad, chair of the department of pharmacy at Chapman University. “We have an effective vaccine for influenza, and there’s still time to get it if you haven’t been vaccinated this season.”

Trump has repeatedly downplayed the coronavirus threat, saying it was "under control.''

"The people are getting better. They're all getting better," Trump said Tuesday. "I think that whole situation will start working out. A lot of talent, a lot of brainpower is being put behind it."

On Wednesday, Trump noted the flu has had much more impact than the coronavirus, saying he was amazed to find out influenza kills more than 25,000 Americans every year. There have been no reported fatalities in the U.S. because of the new virus.

"That was shocking to me,'' Trump said of the annual flu toll. "So far, if you look at what we have with the 15 people, and they're recovering.''

Contributing: Kevin McCoy, USA TODAY