MONDAY, Feb. 3, 2020 (HealthDay News) -- While health experts fear that the coronavirus outbreak in China will become a pandemic as infections topped 17,000 worldwide, U.S. officials reported three more cases in California, bringing the total in this country to 11.

A pandemic, which is when there are epidemics occurring on two or more continents, is looking more likely by the day, as the World Health Organization (WHO) reports there are now 146 cases in at least 23 countries outside China.

On Sunday, three more U.S. cases of coronavirus were reported in California -- a couple in San Benito County and a woman in Santa Clara, Calif. The couple is believed to be the second instance of person-to-person transmission in the United States, according to the U.S. Centers for Disease Control and Prevention.

Also on Sunday, the United States began to bar entry to any foreigners who have recently traveled to China. The move was announced by U.S. Health and Human Services Secretary Alex Azar on Friday as he declared the coronavirus a "public health emergency."

Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said the American actions were being taken because there are "a lot of unknowns" surrounding the virus and its transmission path, The New York Times reported.

"The number of cases have steeply inclined with every day," Fauci noted.

The temporary entry ban applies to foreign nationals, with the exception of relatives of citizens and permanent residents, the Times reported.

U.S. citizens who have recently traveled to the Hubei province of China, where Wuhan is located, will be quarantined for up to 14 days, U.S. health officials said. U.S. citizens who have recently traveled to other parts of China will face health screenings and voluntary quarantines of up to 14 days.

"This is an aggressive action by the United States, but our goal is to slow this thing down," Dr. Nancy Messonnier, director of the U.S. National Center for Immunization and Respiratory Diseases, said during a Monday media briefing. "We have the opportunity to slow it down before it gets into the United States," she explained.

"We felt, scientifically, our recommendation was if we acted now we did have the opportunity to provide additional protection to the United States and Americans," she added. "So we made an aggressive decision in front of an unprecedented threat that action now would have the biggest potential to slow this thing down."

The WHO has already declared the coronavirus outbreak an international public health emergency.

On Friday, U.S. health officials also announced a mandatory quarantine for the 195 Americans who were evacuated last week from Wuhan, the epicenter of the outbreak.

Messonnier noted Monday that the U.S. State Department will be bringing more people home from Wuhan. Flights are expected this week.

"Over the weekend, CDC sent four additional teams to specific Department of Defense locations where those planes will arrive," she added.

"These passengers will be under federal quarantine for 14 days from when the planes left Wuhan, same as the 195 folks" who were evacuated last week.

"If we take strong measures now, we may be able to blunt the impact of the virus on the United States. While we recognize this is an unprecedented action, we are facing an unprecedented public health threat," Messonnier said Friday.

"We are preparing as if this were the next pandemic, but we are hopeful still that this is not and will not be the case," she added. "This is the first time in 50 years that CDC has issued a quarantine order. We would rather be remembered for overreacting than for underreacting."

Meanwhile, Chinese officials said Monday that the death toll in that country has hit 361, the Times reported. Chinese health officials have confirmed that the virus is spreading from person-to-person, and that it can be spread by a person who is not showing symptoms of infection.

Outside China, there have been more than 146 confirmed cases of coronavirus in at least 23 countries. The first death outside China, a man from Wuhan who was visiting the Philippines, was confirmed Sunday, the Times reported.

Cases recorded in Thailand, Taiwan, Germany, Vietnam, Japan, France and the United States have involved patients who had not been to China.

More information

The U.S. Centers for Disease Control and Prevention has more on the new coronavirus.