It’s spreading.

Over the course of several hours on Friday, officials in three states announced that residents with no known risk factors, such as travel to global hot spots, had tested positive for the new coronavirus.

In each case, health authorities believe the patient contracted the illness from someone locally—an anticipated but still alarming scenario that sets the stage for an explosion in diagnoses.

It began with a news conference in Santa Clara County, California, where officials said an older woman went to her doctor with symptoms of COVID-19, as the disease caused by the virus is officially known, and subsequently tested positive.

Hours later, Oregon officials called a press conference with even more concerning news: A school employee had tested positive and may have exposed an untold number of elementary school staff and students.

That briefing was barely over when authorities in Washington state assembled to reveal that a high-school student who had been on campus just that morning also had the virus.

Each announcement raised crucial questions: How did the patient contract the virus; did the person who infected them spread it to others who have not been identified yet; and did they also pass it on before they were diagnosed?

Health investigators in all three states are now scrambling to trace the movements of the patients and identify and inform their close contacts in a feverish attempt to stop the virus from spreading out of control like it has some places abroad.

In Oregon and in Washington, the schools linked to the patients were shut down as officials tried to forestall panic.

“We’ve been expecting this and we are prepared for it,” Patrick Allen, director of the Oregon Health Authority, told reporters.

Hundreds of Americans have been in quarantine after returning from coronavirus hot spots such as China or cruise ships in the Pacific, but because they are isolated, they represent little risk to the general population.

The real concern is those who have been moving freely in the community while infected, before they know they have COVID-19, potentially spreading the virus to anyone who has prolonged contact within 6 feet.

“Passing someone on the street or in the store isn’t going to put them at risk,” Dr. Jennifer Vines said at the Oregon news conference.

The Oregon school employee, who lives in Washington County and works in Clackamas County, fell ill on Feb. 19 and sought care at Kaiser Permanente Westside Medical Center.

On Friday afternoon, a public health lab in Hillsboro—which had just been certified to perform coronavirus testing—reported the worker was positive for COVID-19.

The diagnosis has been labeled presumptive, which means the results still have to be confirmed by the U.S. Centers for Disease Control, but local authorities are proceeding as if it’s a bona fide case.

The worker is still in the hospital, in isolation, though officials declined to provide their condition, citing privacy concerns. They also would not specify the patient’s age, their gender, or their job title.

They said only that the worker had spent time at Forest Hills Elementary School, and the Lake Oswego School District announced the school would be closed until March 4.

Health officials have been monitoring dozens of Oregon residents who have traveled in coronavirus-hit countries like China since the outbreak began. But the school worker doesn’t fall into that category.

“This is a case of community spread of the disease,” Allen said, adding, “We don’t know how this person became infected.”

A second Oregon resident with symptoms is being tested, but that person has no known connection to the school worker—which means there is at least one other person in the state who has the novel coronavirus but has not been identified.

“The case count may very well tick up,” Vines said.

The Washington student fell sick Monday with fever, body aches, and a headache, and was seen at two clinics in Snohomish County. The teen felt better by Friday morning and returned to Jackson High School—only to be notified soon after that they tested positive.

“The few students they were in contact with have been notified and will remain home for 14 days with symptom monitoring by the Snohomish Health District,” the school district said in a letter to parents.

“The student has a sibling at Gateway Middle School who is not symptomatic, but out of an abundance of caution, is being tested and will remain out of school in quarantine until tests results are back.”

The high school will be closed on Monday to give workers extra time to clean the premises. And the clinics the teen visited were notified so health workers and other patients there can be monitored.

The new California patient is a 65-year-old woman with pre-existing medical problems. She went to the doctor, who asked for coronavirus testing on Wednesday. It came back positive on Friday.

Like the Oregon and Washington patients—and like another California resident diagnosed on Wednesday in Solano County—the woman had not traveled and had no known contact with anyone known to have COVID-19.

While health officials in all three states stressed that most people who get coronavirus will have mild symptoms and an easy recovery, they also said that Friday’s developments are just the beginning.

As more state labs are approved to carry out testing, the number of people diagnosed is sure to climb.

“I understand this may be concerning to hear, but this is what we have been preparing for,” said Dr. Sara Cody, health officer for Santa Clara County. “Now we need to start taking additional actions to slow down the spread of the disease.”

COVID-19, which originated in an animal market in Wuhan, China, is now on every continent except Antarctica. The World Health Organization has not yet declared it a global pandemic but on Friday upgraded the risk of it spreading to the highest level.

President Donald Trump this week created a task force, headed by Vice President Mike Pence, to address the spread in the U.S., though he has also claimed that his political enemies are hyping up fears to damage him in an election year.