In a troubling turn in the nation’s fight against the new coronavirus, a second U.S. case of unknown origin was confirmed Friday in Santa Clara County.

The case — an adult woman with pre-existing health problems, reportedly receiving care at Mountain View’s El Camino Hospital — is the second this week in which the infected person had no known exposure to the coronavirus either through travel overseas or another infected person. The first case also arose in the Bay Area, in Solano County.

And Oregon health officials late Friday reported their own coronavirus case of unknown origin, which would be the country’s third. It involves a Lake Oswego elementary school employee, according to the Oregonian.

In the state of Washington, a person infected with the virus died, according to the Seattle and King County Department of Health. The fatality marks the first death associated with the virus in the United States.

The Santa Clara County woman had not traveled to Solano County, site of Travis Air Force Base’s quarantine of Diamond Princess passengers. That news is alarming because it suggests the coronavirus may be spreading undetected in the Bay Area, possibly in at least two different places and populations.

“This case represents some degree of community spread, some degree of circulation,” said Dr. Sara Cody, Health Officer for Santa Clara County and Director of the County of Santa Clara Public Health Department.

“But we don’t know to what extent,” she said. “It could be a little, it could be a lot.”

The news came on a day when the World Health Organization raised its risk assessment of the coronavirus to “very high,” citing its potential spread and impact. The assessment is the highest level short of declaring a global pandemic.

Also on Friday, the U.S. stock market fell for the seventh straight day, logging the worst weekly loss since the 2008 recession, amid fears of global economic damage from the coronavirus outbreak.

Dr. Cody urged local residents, businesses and schools to start planning for the prospect of a broader outbreak.

“We need to begin taking important additional measures to at least slow it down as much as possible,” she said.

These strategies range from the personal and simple, such as frequent hand washing, to the larger and more complex, such as implementing more flexible telecommuting policies at work, installing study-at-home plans for schools and creating more generous absentee policies at both work and school.

“Start thinking about family preparedness — what you would need to do to stay home for a week or two,” she said. “We understand it may feel overwhelming and difficult to think about possible disruptions to everyday life.”

The infected patient is an older adult woman with chronic health conditions who was hospitalized for a respiratory illness, county officials said. The Washington Post, citing an unnamed source, reported that the woman is 65 years old.

Suspicious of her symptoms, her infectious disease physician on Wednesday contacted the Public Health Department to discuss the case and request testing for the novel coronavirus.

The Santa Clara County Public Health Laboratory received the specimens Thursday and conducted the test on site, confirming the infection on Thursday evening. The county just gained the ability to do such rapid confirmation Wednesday; previous tests have had to be analyzed in a center in Atlanta, creating a time lag that had caused deep concerns.

Santa Clara County now is working to identify the woman’s contacts and understand the extent of exposure. Health care workers were exposed and are now quarantined, said Cody. According to a nurse who wished to remain unidentified, the patient is at El Camino Hospital in Mountain View.

Eight public health labs in California now have the ability to test for coronavirus. In addition to labs in Santa Clara County and Sacramento, there are tests available in the counties of Alameda, Tulare, Ventura, Los Angeles, Orange and San Diego. Federal officials said late Friday they are dispatching another 1,200 test kits to California.

On Wednesday, health officials confirmed that a woman in Solano County also had become infected with no known exposure to the disease through travel to China where the outbreak was first reported or other overseas hotspots, the first such U.S. case.

Late Friday, Solano County health officials announced an additional confirmed case involving a county resident who had been taken to Travis Air Force Base in Fairfield from the Diamond Princess cruise ship where an outbreak erupted while docked in Japan. A second county resident also at Travis who had tested positive in Japan is awaiting confirmation of results from U.S. testing.

That would bring the total confirmed cases in the U.S. to 64. Of those, 45 were people who had been aboard the Diamond Princess cruise ship and repatriated to the U.S., three were repatriated from Wuhan, 12 were people who had recently traveled in China and two caught it from a close family member. Then there are the two cases in Solano and Santa Clara counties involving people with no known exposure risk.

It is also the third case of the novel coronavirus disease, known as COVID-19, in Santa Clara County. County officials announced their first case, and the first in Northern California, on Jan. 31.

But the previous cases, unlike the new case, involved risk factors that were well known: They had traveled to China.

County officials said Friday that local schools should plan for absenteeism and explore options for tele-learning and enhance surface cleaning. Late Friday, Palo Alto Unified School District announced that a parent of two students may have been exposed and that the students have been sent home as a precaution until further notice.

Businesses, they said, should conduct meetings by video or telephone conference where possible, increase tele-working options and modify absenteeism policies and also enhance surface cleaning.

Dr. Christopher Braden, Deputy Director of the National Center for Emerging and Zoonotic Infectious Diseases at the U.S. Centers for Disease Control and Prevention, said the new coronavirus can survive on surfaces for days but can be killed by disinfectants. But Cody added that the likely mode of infection is person to person.

People should observe standard hygiene measures to avoid infection, health officials said, such as avoiding sick people and close contact with others, regularly washing hands and avoiding touching their eyes, nose and mouth.

The El Camino nurse, who did not want to be identified, said staff were frustrated and worried about the lack of available tests from the U.S. Centers for Disease Control and Prevention, as well as the lack of protective gear such as N95 respirator masks to protect health care workers treating the sick. The nurse said a doctor and several emergency room staff have been quarantined.

“We’re in Silicon Valley, the richest economy in the world and we don’t have enough N95 masks,” the nurse said. “It’s insanity. Everybody is worried about it. I’m just worried about containment. It’s so contagious.”