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Three new confirmed or presumptive cases of the coronavirus illness COVID-19 contracted from an unknown source were reported Friday, bringing the total number of what could be "community spread" cases in the United States to four.

The patients from these four cases have no known travel history or exposure to someone who had traveled or been infected. Not all four have been confirmed by Centers for Disease Control and Prevention testing, but they tested positive locally.

New cases were reported in Washington state, Oregon and California on Friday. Earlier this week, a patient at a Sacramento hospital with no known source of infection was confirmed by CDC testing to have the illness.

The case in Washington state in Snohomish County involves a high school student, health officials said. The student is said to be doing well and did not attend classes after developing symptoms earlier this week. The student felt better and tried to go back to school Friday morning but the test came back positive and the student returned home before attending class.

"There was no travel history associated with this case. Our team is still in the midst of the contact investigation, so we do not yet know the possible source of infection," Snohomish Health District Health Officer Dr. Chris Spitters said.

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Spitters urged the public to remain calm and informed.

Oregon health officials said Friday that someone who had spent time in an elementary school tested positive for COVID-19 in a local test, and the source of that infection is not yet known. Contact tracing is being conducted and is a top priority, Oregon Health Authority Director Pat Allen said.

The CDC test to confirm is pending. It is the first presumptive case in Oregon. Health officials say they are prepared for cases of the coronavirus illness in the state.

On Friday, the Santa Clara, California, county health department said that a COVID-19 case confirmed there involved an adult woman who does not have a travel history nor any known contact with a traveler or infected person.

"This new case indicates that there is evidence of community transmission, but the extent is still not clear," Dr. Sara Cody, health officer for Santa Clara County and director of the County of Santa Clara Public Health Department, said in a statement. "I understand this may be concerning to hear, but this is what we have been preparing for. Now we need to start taking additional actions to slow down the spread of the disease."

"Community spread" is a term used when someone is infected but the source is unknown.

Previously much of the focus seemed to be on people who had visited such places as Wuhan, China, where the outbreak began, or who had been in close contact with people who were infected.

The CDC adjusted its testing guidance this week to include people with symptoms but with no identified source of exposure.

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The first case of COVID-19 in the United States which may involve community spread was confirmed by a CDC test on Wednesday. That patient is at UC Davis Medical Center in Sacramento, California, and involves a woman from Solano County, officials have said.

The CDC said in a statement Friday it is aware of the cases announced Friday, and that it is prepared.

"Unprecedented, aggressive efforts have been taken to contain the spread and mitigate the impact of this virus. CDC and federal partners have been preparing for the detection of additional instances of person-to-person spread of COVID-19 for weeks," the centers said in a statement.

Officials have stressed that the best defense against contracting the novel coronavirus that causes the COVID-19 illness is preventative measures including washing hands with soap and water; routinely cleaning frequently touched surfaces and objects; and covering coughs and sneezes, among other measures.