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.
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."
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."
"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.
The U.S. embassy in Beijing on Sunday issued a notice saying the American consulate in Wuhan will evacuate its staff and some private citizens on a charter flight Tuesday to San Francisco, though seat numbers will be limited. The embassy said priority will be given to those "at greater risk" from the virus, which can progress to pneumonia and is a greater threat to the elderly and people already suffering from respiratory problems.
Chinese authorities have restricted travel for 17 cities in its central Hubei province, where Wuhan is located. It is an area encompassing more than 50 million people. Wuhan itself — where the virus first appeared, reportedly in a seafood market also selling wildlife including snakes and marmots — has a population of 11 million.
Hubei on Sunday shut down inter-city and inter-province buses in an effort to curb the outbreak.
On Saturday, Hong Kong leader Carrie Lam declared a virus emergency in the city of 7.3 million, halting all official trips to mainland China, extending school cancellations and scrapping official plans for the Lunar New Year, China's busiest travel week.
Australia confirmed its first four cases of the virus on Saturday and expects more, its health authorities said, as the country is a popular destination for Chinese tourists. While the majority of confirmed coronavirus cases and deaths are in mainland China, the virus has also been identified in Japan, South Korea, Taiwan, Thailand, Vietnam, Singapore, Nepal, France, Australia and the U.S.
The World Health Organization (WHO) has so far declined to declare the disease a global health emergency, and said it needs more data. The virus is currently spreading through human-to-human contact and in medical settings, the organization said.
Coronaviruses are a large family of viruses that tend to primarily affect animals, but can evolve and spread to humans. Symptoms for the strain currently moving around the globe include fever, coughing and shortness of breath, and it can progress to pneumonia. Little is currently known about this new strain of coronavirus, and the medical community has yet to develop a cure for it.
The coronavirus family also includes the SARS virus (severe acute respiratory syndrome), which infected more than 8,000 people and killed 775, mostly in China, during its nine-month outbreak which ended in 2003.
Former FDA Commissioner Scott Gottlieb told CNBC on Friday that coronavirus was likely more contagious, but less severe, than SARS.
"But the question is, has it achieved sort of that golden point where it's contagious enough to spread rapidly but still severe enough to cause a lot of harm?" he said during an interview on "Squawk Box."
"We don't know that yet," he said.
— Correction: This story has been updated to reflect the correct spelling for the name of Hong Kong's leader Carrie Lam.