A mandatory quarantine for medics who treated victims of the disease in West Africa has been ordered in New York and New Jersey on Friday.
The new measures were ordered by state governors Andrew Cuomo and Chris Christie the day after an American doctor tested positive for Ebola one week after returning from working in hard-hit Guinea.
Craig Spencer, 33, was in stable condition in isolation at Bellevue Hospital Center on Friday as he underwent treatment for the illness, which has killed nearly 4,900 people -- most of them in West Africa.
The New York case revived fears about the possible spread of the virus in US cities, but a glimmer of hope came with the news that two Texas nurses infected while treating a Liberian man are now free of the virus.
In Manhattan, Cuomo and Christie announced additional screening protocols at JFK and Newark international airports at a joint press conference.
Steps include mandatory quarantine for up to 21 days of any individual who has had direct contact with an Ebola patient while in Guinea, Liberia or Sierra Leone, including medics who treated Ebola patients.
Additionally, anyone who has travelled to the affected regions but not had direct contact with an Ebola patient will be actively monitored by public health officials and quarantined if necessary.
Christie said that a health care worker who arrived at Newark with a recent history of treating patients with Ebola in West Africa, but who had no symptoms, had been placed in quarantine.
Spencer was rushed to the hospital with fever and gastrointestinal symptoms on Thursday, a week after returning from a stint in West Africa with the charity group Doctors Without Borders.
His live-in fiancee and two of his close friends are in quarantine but healthy, officials said.
- 'No cause for alarm' -
New York Mayor Bill de Blasio, Cuomo and other officials sought to allay fears that Spencer had put New Yorkers at risk by using the subway, going bowling and eating out before falling ill.
"There is no cause for alarm," de Blasio said. "New Yorkers need to understand the situation is being handled and handled well."
"We are fully prepared to handle Ebola. Our medical experts here in the city have been studying this disease intensively and working closely with our federal partners," de Blasio said.
New York, one of the largest points of entry to the United States, had been braced for months for a possible Ebola case.
The area's two largest international airports, JFK and Newark, this month introduced health checks for passengers travelling from West Africa, and four city hospitals are equipped to cope with Ebola patients.
Spencer, who returned home through JFK on October 17, is the first case diagnosed in the United States outside Texas.
In Dallas, two nurses contracted the virus after treating a Liberian patient who later died of Ebola.
-Obama hug for cured Ebola nurse-
The nurses were declared cured on Friday, and 26-year-old Nina Pham was healthy enough to leave hospital and meet President Barack Obama for a hug at the White House before returning home.
Obama has been vocal in calling on Americans not to give in to fear or hysteria, stressing that Ebola does not spread easily and that the United States is well-equipped to deal with any new cases.
Pham smiled and appeared healthy, wearing a turquoise shirt and dark business suit at a news conference outside the National Institutes of Health Clinical Center in Bethesda, Maryland.
"I feel fortunate and blessed to be standing here today," she said, expressing her gratitude for those who prayed for her and cared for her while she was sick.
Pham was the first US health care worker to be infected with Ebola while working inside the United States, catching the disease from Thomas Eric Duncan, who was admitted to Texas Health Presbyterian Hospital Dallas on September 28.
Her colleague, Amber Vinson, also become infected. She, too, is clear of the virus but has not yet been released from Emory University Hospital in Atlanta, Georgia.
"Tests no longer detect virus in her blood," the hospital said, adding that Vinson would stay in the serious communicable diseases unit for continued supportive care until further notice.
Pham and Vinson worked in the intensive care unit, though it remains unknown exactly how they were infected.
The US Centers for Disease Control and Prevention said a "breach of protocol" was to blame, and has since issued stricter guidelines for donning protective gear when caring for Ebola patients.