New York and New Jersey will automatically quarantine medical workers returning from Ebola-hit West African countries and the U.S. government is considering the same step after a doctor who treated patients in Guinea came back infected, officials said on Friday.

The steps announced by the two states, which go beyond the current restrictions being imposed by U.S. President Barack Obama's administration on travellers from Liberia, Sierra Leone or Guinea, came as medical detectives tried to retrace the steps in New York City of Craig Spencer, who tested positive for Ebola on Thursday.

Spencer, who returned from Guinea on Oct. 17, rode the subway, ate out, took a cab and went bowling in the Brooklyn borough since he got back

Craig Spencer doctor new york ebola

Dr. Craig Spencer, New York City's first Ebola patient, is a member of Doctors Without Borders. He is being treated in an isolation ward in Manhattan's Bellevue Hospital, a designated Ebola centre. (Craig Spencer/LinkedIn)

The new policy applies to medical workers returning from the region through John F. Kennedy International Airport in New York and Newark Liberty International Airport in New Jersey. In the first instance of the new move, a female health-care worker who had treated patients in West Africa and arrived at the Newark, New Jersey, airport was ordered into quarantine.

"Voluntary quarantine is almost an oxymoron," New York Gov. Andrew Cuomo said. "We've seen what happens ... You ride a subway. You ride a bus. You could infect hundreds and hundreds of people."

"It's too serious a situation to leave it to the honour system of compliance," Cuomo said.

Possible nation-wide policy

Cuomo, who appeared at a news conference with the governor of neighbouring New Jersey, Chris Christie, had earlier in the day sought to reassure New Yorkers that Ebola's threat was limited the day after Spencer tested positive for the virus.

Cuomo said the U.S. Centers for Disease Control and Prevention had agreed that individual states have the right to exceed federal requirements.

A federal quarantine of health-care workers returning to the U.S. from the three West African countries was one of a number of options being discussed by administration officials, Tom Skinner, a CDC spokesman, told Reuters.

Spencer, 33, who spent a month with the humanitarian group Doctors Without Borders in Guinea, was the fourth person diagnosed with the virus in the U.S. and the first in its largest city.

Dr. Mary Travis Bassett, New York's health commissioner, said Spencer was awake and talking to family and friends by cellphone and was listed in stable condition in Bellevue Hospital's isolation unit. Meanwhile, workers in biohazard gear began cleansing Spencer's apartment in upper Manhattan.

The virus is not airborne but is spread through direct contact with bodily fluids from an infected person who is showing symptoms.

No travel ban

The Obama administration has implemented a series of steps aimed at preventing the further spread of Ebola in the U.S. but has stopped short of a travel ban on people from Liberia, Sierra Leone or Guinea called for by some politicians.

The U.S. is funnelling travellers from those countries through five airports conducting special screening for signs of infection and is requiring them to report to health authorities for the 21-day Ebola virus incubation period.

Ebola virus outbreak Chris Christie Andrew Cuomo

Governors of N.J. Chris Christie (R) and of N.Y. Andrew Cuomo announced Friday that those states will implement a mandatory 21-day quarantine for all people who had contact with Ebola victims in West Africa. (Carlo Allegri/Reuters)

"We want to strike the right balance of doing what is best to protect the public's health while not impeding whatsoever our ability to combat the epidemic in West Africa. Our risk here will not be zero until we stop the epidemic there," Skinner said.

White House spokesman Josh Earnest declined to discuss the possibility of a nation-wide quarantine policy but said "these kinds of policy decisions are going to be driven by science" and the advice of medical experts.

Spencer finished his work in Guinea on Oct. 12 and arrived at John F. Kennedy International Airport in New York five days later. Six days later, he was quarantined with Ebola.

Three people who had close contact with Spencer were quarantined for observation. The doctor's fiancée was among them and was isolated at the same hospital, and all three were still healthy, officials said.

The worst Ebola outbreak since the disease was identified in 1976 has killed at least 4,877 people and perhaps as many as 15,000, predominantly in Liberia, Sierra Leone and Guinea, according to the World Health Organization. On Friday, health officials in Mali revealed that the first person to be diagnosed with the virus in that country, a 2-year-old girl, had died of the disease

With files from The Associated Press and CBC News