A laboratory technician works with a pipette at the Institute of Virology at the Charité Berlin Mitte, where investigations on coronavirus are underway.

The fifth U.S. case of coronavirus was confirmed on Sunday in Maricopa County, Arizona, by the Centers for Disease Control and Prevention, the health agency said during a call with reporters.

The announcement came after health officials in California announced that two cases had been confirmed earlier in the day in Los Angeles and Orange counties.

All five cases involve individuals who were described as recent travelers from Wuhan, China — the epicenter of the disease's outbreak and where the majority of cases have been reported. The CDC said that all five patients remain hospitalized. There are about 100 patients who the CDC is investigating for possibly having the virus, the agency said.

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On Monday, Chinese health authorities said there were 2,744 confirmed cases of pneumonia caused by the virus, with 461 in critical condition, according to a state media report. The report also said 80 people have died.

According to the CDC's guidance, people who have "casual contact with a case" — for instance, those in the same grocery store or movie theater — "are at minimal risk of developing infection."

The CDC said it was currently monitoring individuals who may have come into close contact with the patients with the virus.

Authorities in Orange County, which borders Los Angeles County to the south, said in a statement earlier in the day that the Orange County patient is in isolation in a hospital and is in "good condition."

Authorities in Los Angeles did not disclose how the Los Angeles patient was faring but said the person was "currently receiving appropriate care."

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Los Angeles officials said they were working to identify individuals who may have come into contact with the Los Angeles patient but that here was "no immediate threat to the general public."

Orange County health officials said they will be monitoring any close contacts, but that there is "no evidence that person-to-person transmission has occurred in Orange County."

This map shows the latest spread of the coronavirus

"The current risk of local transmission remains low," the Orange County health officials said, echoing the CDC's prior statements that the U.S. public is not at high risk of transmission. But it said the situation "continues to evolve rapidly."

The first two U.S. cases of the virus were a Washington state man in his 30s and later, an Illinois woman in her 60s. Both had traveled to Wuhan, and are currently reported to be in a stable condition at area hospitals.