Health officials on Friday confirmed two new cases of coronavirus in the US believed to have been transmitted to people who had not traveled to other affected countries or come in close contact with anyone who had it.

The US Centers for Disease Control and Prevention (CDC) said on Friday that officials were “aware of a second possible instance of community spread of Covid-19 in California”, following an earlier such case this week in the state. Hours later, Oregon officials described that state’s first case, saying the patient “had neither a history of travel to a country where the virus was circulating, nor is believed to have had a close contact with another confirmed case”.

The CDC said in a statement that the California patient had tested positive for the virus and was considered a presumptive positive case.

Health officials in San Jose said the patient was an older adult woman with chronic health conditions who did not have a travel history or any known contact with a traveler or infected person. It comes a day after state officials said a woman hospitalized at UC Davis health center in Sacramento had contracted the illness after no known contact.

“This new case indicates that there is evidence of community transmission but the extent is still not clear,” said Dr Sara Cody, health officer for Santa Clara county and director of the county of Santa Clara public health department.

The infected person in Oregon worked at an elementary school in the Portland area, which will be temporarily closed while it is deep-cleaned, authorities said. Officials planned to spend the weekend scrambling to find everyone the unidentified person, who has been hospitalized, had been in contact with.

On Thursday, state health officials announced that a woman in Vacaville was believed to be the first in the US to be infected without traveling internationally or being in close contact with anyone who had it.

As infectious disease experts fanned out in Vacaville, some residents in the city of 100,000 stocked up on supplies amid fears things could get worse despite official reassurances, while others took the news in stride.

Vacaville lies between San Francisco and Sacramento in Solano County, in the agricultural Central Valley and near California’s famous wine region. It is about 10 miles (16km) from Travis air force base, which has been used as a virus quarantine location. Public health officials said they can find no connection between the infected woman and passengers on the Diamond Princess cruise ship who were evacuated to the base when the ship was docked in Japan.

The case of the infected woman marked an escalation of the worldwide outbreak in the US because it means the virus could spread beyond the reach of preventive measures like quarantines, though state health officials said that was inevitable and that the risk of widespread transmission remains low.

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The Solano county public health officer Dr Bela Matyas said public health officials had identified dozens of people, but less than 100, who had close contact with the woman. They are quarantined in their homes and a few who have shown symptoms are in isolation, Matyas said.

Officials are not too worried, for now, about casual contact, because federal officials think the coronavirus is spread only through “close contact, being within six feet of somebody for what they’re calling a prolonged period of time”, said Dr James Watt, interim state epidemiologist at the California department of public health.

The virus can cause fever, coughing, wheezing and pneumonia. Health officials think it spreads mainly from droplets when an infected person coughs or sneezes, similar to how the flu spreads.

The case in Vacaville also raised questions about how quickly public health officials are moving to diagnose and treat new cases. State and federal health officials disagreed about when doctors first requested the woman be tested.

Doctors at the UC Davis medical center in Sacramento said they asked the CDC to test the woman for the virus on 19 February. But they said the CDC did not approve the testing until Sunday “since the patient did not fit the existing CDC criteria” for the virus, according to a memo posted to the hospital’s website.

The woman first sought treatment at NorthBay VacaValley Hospital in Vacaville, before her condition worsened and she was transferred to the medical center.

A CDC spokesman, Richard Quartarone, said a preliminary review of agency records indicated the agency did not know about the woman until Sunday, the same day she was first tested.

National Nurses United, the union of registered nurses, warned on Friday that Vacaville case highlighted the vulnerability of the nation’s hospitals to this virus and the insufficiency of current CDC guidelines. “Lack of preparedness will create an unsustainable national healthcare staffing crisis,” the union said in a statement.

