The Carnival cruise ship Carnival Magic is seen in port in Galveston, Texas on Sunday. The Carnival Magic arrived on Sunday after a week-long trip with a Dallas hospital lab worker on board who spent much of the cruise in isolation after possible exposure to Ebola.

Reuters/Galveston, Texas

A Dallas hospital lab worker who spent much of a cruise holiday in isolation after possible exposure to Ebola has tested negative for the disease, and in Texas some of the dozens of people still being monitored were expected to be cleared on Sunday and Monday.

The Carnival Magic docked in the port of Galveston, Texas after a week-long cruise that included being denied docking by Belize and Mexico because of the presence of the woman on board.

The precautions taken over the Texas lab worker reflected anxiety over the spread of Ebola.

Three cases of the disease have been diagnosed in the US, and dozens of people are being monitored having been exposed to the three patients.

The worst outbreak on record of the virus, which is spread by contact with bodily fluids of sick people, has killed more than 4,500 people, mostly in the West African countries of Liberia, Sierra Leone and Guinea.

Liberian President Ellen Johnson Sirleaf urged stronger international action to bring the epidemic under control on Sunday, saying the disease is unleashing an economic catastrophe that will leave a "lost generation" of young West Africans.

The lab worker who was being monitored aboard the cruise liner worked at the Texas Health Presbyterian Hospital where a Liberian man, Thomas Eric Duncan, was treated for Ebola.

The worker, who has not been named, did not have contact with Duncan but was being monitored as she might have come in contact with test samples from Duncan. Two nurses who treated Duncan, who died on October 8, have contracted the disease.

Texas state authorities said 14 people had been cleared from an Ebola watch list. On Sunday and Monday, more were expected to end 21 days of monitoring for fever and other symptoms. The incubation period for the virus is up to 21 days.

They could include Duncan's fiancee, Louise Troh, her 13-year-old son and two other people who have been in mandatory quarantine at an undisclosed location in Dallas.

In all, 145 people with "contacts and possible contacts" with the virus were being monitored, the Texas Department of State Health Services said in a statement on Saturday. The dates when the 145 people began monitoring varies.

US President Barack Obama sought to put the extent of the disease in the US in perspective in his weekly radio address on Saturday.

"What we're seeing now is not an 'outbreak' or an 'epidemic' of Ebola in America," he said. "This is a serious disease, but we can't give in to hysteria or fear."

A series of Ebola scares has hit the country since Duncan, who fell ill in September while visiting Texas, was diagnosed. Americans' faith in the medical system and in its disease prevention ability was jolted by early missteps in his case.

In a public letter on Saturday night, Texas Health Resources chief executive Barclay Berdan acknowledged that the Texas Health Presbyterian Hospital where Duncan first went, made mistakes, including initially not diagnosing Ebola.

Berdan said aggressive actions since then ensured that the hospital was a safe place, and that outside experts would be consulted to determine how two nurses became infected.

Nurse Amber Vinson is being treated at Atlanta's Emory University Hospital, while her colleague Nina Pham is being treated at the National Institutes of Health outside Washington.

Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said he had a long conversation Saturday night with Pham.

"She's in good spirits," Fauci told Fox News Sunday. Asked whether she would recover, Fauci said, "I'm feeling good about the fact that she's progressing very well."

People who had contact with the nurses or Duncan are being monitored, while some 800 passengers who flew with Vinson on a trip she made to Ohio before being diagnosed, as well as those on subsequent flights on the same planes, have been contacted by Frontier Airlines, it said on Saturday.