The country has the largest coronavirus outbreak outside of China, with a total of 3,150 cases.

President Trump described Democrats’ concerns about the virus as “their new hoax.”

New cases in three U.S. states raise prospect of local, person-to-person spread.
Troubling new signs of how the coronavirus is spreading in the United States emerged on Friday, as cases not explained by overseas travel or contact with a person known to be infected were reported in California, Oregon and Washington State.

Officials from the three states announced that their testing had found new cases: a high school student from Washington State; an employee of a school in Oregon, near Portland; and a woman in Santa Clara County, Calif., in the heart of Silicon Valley.

Sixty-five cases of the virus have been reported in the United States, but until this week, all of them could be explained by overseas travel or contact with someone who had been ill. The three new cases on Friday, and a case earlier in the week, in California, were the first in the United States in which the cause was mysterious and unknown — a sign, experts warned, that the virus might now be spreading in this country.

“If we were worried yesterday, we are even more worried today,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center. “Now we have to ask: How widely, really widely, is this virus out there?”

As word emerged of the unexplained cases, local officials scrambled to trace everyone who had come in contact with those who were ill. California health officials said they were increasing testing. And in Washington State, officials suggested that people needed to prepare for the possibility of schools closing and businesses keeping workers home.

“We’re going to be increasingly recommending that people try and avoid crowds and close contact with other people,” Dr. Jeff Duchin, health officer for Public Health Seattle & King County, said. “We may get to a point where we want to recommend canceling large public gatherings — social events, sporting events, entertainment — until we get over a hump of what might be a large outbreak.”