Voluntary quarantine protocols have been applied to about 700 people who returned to New York after traveling to areas affected by the coronavirus outbreak in China since Feb. 3, authorities said.

The vast majority of the travelers were deemed at medium risk for the new coronavirus, called COVID-19, because of recent travel to mainland China, New York State Health Department officials told the USA TODAY Network New York late Tuesday.

The newly reported tally reflected travelers reviewed for potential voluntary quarantine outside New York City.

None of the 700 people had symptoms, and the number of them being monitored by local health officials during a 14-day self-isolation period was changing almost daily, in part, due to ongoing travel from mainland China, state health officials said.

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The number of travelers being watched underscored the scope of the public-health response underway in New York and across the country as the virus spread across the globe.

A federal health official warned Tuesday that the deadly coronavirus could cause "severe" disruptions in the USA as global experts struggled to fend off the outbreak and avoid a pandemic.

The global death toll from coronavirus rose to 2,770 on Wednesday, with more than 81,000 confirmed cases, including 57 in the U.S. None of the confirmed cases have been in New York.

What to know about coronavirus voluntary quarantine

On a daily basis, the Centers for Disease Control and Prevention provides state health officials with names and contact information of travelers from China screened by U.S. Customs and Border Protection, according to Jill Montag, a state Health Department spokeswoman.

So far, local health departments have contacted about 700 of the travelers since early February to determine if they meet the criteria for self-isolation, Montag said. She would not provide details about the locations of the people on quarantine.

Westchester County, located just north of New York City, announced last week that it is monitoring 26 travelers on voluntary quarantine, mostly in their homes. Neighboring Rockland County disclosed it had two people on similar quarantine, and another three people who had completed the 14 day self-isolation. No information was available for Nassau and Suffolk Counties on Long Island.

Health officials upstate in Monroe County, which includes Rochester, were monitoring six people earlier this month.

At a press conference on Wednesday, New York City Mayor Bill de Blasio did not elaborate on the number of self-quarantine cases within the five boroughs of Manhattan, Brooklyn, Queens, Staten Island and the Bronx. However, he noted that there are no confirmed cases of coronavirus in the city and said the self-quarantine protocol has been successful because officials have been able to identify nexuses: cases where a person with symptoms had either been to a country with a spike in cases or was in close contact with someone who had.

"We did have a number of people who matched that definition and they consistently went and got health care quickly," he said. "They were therefore isolated from everyone else. The testing happened quickly and the testing came back negative."

De Blasio also called on the CDC to be more proactive in its screening so it can catch possible cases faster.

"Right now, it is too narrowly focused on travelers coming out of China," he said. "We think that needs to be expanded to any traveler coming from a country that's seen a major surge in cases. We think that needs to expanded to any country that now has a travel warning attached to it by the United States government. So I am urging the CDC and the federal government to add the testing protocol upon entry for visitors from Hong Kong, Iran, Italy, Japan, Singapore, South Korea, Taiwan and Thailand."

How self-quarantine works

Returning travelers are asked to voluntarily self-isolate for 14 days after their last potential exposure to novel coronavirus, per CDC guidelines that are based on the virus' incubation period.

During the quarantines, local health departments monitor the individuals for signs and symptoms each day, Montag said.

Common signs of the infection include fever, cough, shortness of breath and breathing difficulties. If it worsens, it can cause pneumonia, severe acute respiratory syndrome, kidney failure or even death.

Montag said the “voluntary self-isolation will help limit the potential for spread of this virus.”

Many of the 700 travelers were deemed medium risk based on CDC guidelines due to their travel from mainland China outside Hubei Province, which includes the epicenter of the outbreak in Wuhan, and not having any exposures that meet a high-risk definition, such as failing to take recommended precautions while living with or caring for a lab-confirmed case of COVID-19.

The voluntary self-isolation includes video monitoring via smartphones and food deliveries overseen by local health officials.

If any of the people on quarantine start showing signs of illness and require transport to a medical facility, the county public safety and emergency services agencies would oversee the transport.

Montag said the number of New Yorkers on voluntary quarantine is also changing because some people have also already completed the 14-day monitoring period.

What to know about cruise ship evacuation, quarantines

The voluntary quarantine protocols differed from the approach being taken to isolate the approximately 380 Americans who were evacuated from the Diamond Princess cruise ship in Japan and flown back to the U.S. on Feb. 17.

Most of the evacuees involved are now quarantined at military bases in Texas and California. A further 13 – 11 of which have since tested positive for coronavirus – are being treated at the University of Nebraska Medical Center in Omaha.

To date, 40 Americans from the Diamond Princess have tested positive, comprising amajority of the 57 cases in the United States.

On Sunday, Alabama state officials rejected a federal plan to house cruise ship passengers who tested positive for the coronavirus at the FEMA Center for Domestic Preparedness in Anniston.

USA TODAY contributed to this report