WASHINGTON (AFP) - The Texas hospital that cared for the first patient to be diagnosed with Ebola in the United States apologised on Sunday over its handling of the case.

The Texas Health Presbyterian Hospital in Dallas treated a Liberian man, Thomas Eric Duncan, who died of Ebola on October 8. Two nurses who cared for him subsequently contracted the disease and are now being treated in specialist facilities.

"As an institution, we made mistakes in handling this very difficult challenge," the hospital said in a "letter to our community" that was published in Sunday's Dallas Morning News.

The apology came as a lab worker from the hospital who had been on a cruise returned to Texas. Because of fears she may have had contact with Duncan's fluids, she had voluntarily remained in isolation in her cabin.

Carnival Cruise Lines said in a statement that a blood test confirmed she was not infected, and she got off the boat after it returned to Galveston. The liner had been refused entry to Belize and Mexico over fears of the disease.

Duncan had flown from Liberia to Texas to visit family, arriving in Dallas on September 20. He began feeling sick four days later, but was not hospitalised until September 28.

He was sent home after an initial visit to the emergency room, even after he reported Ebola-like symptoms and said he had recently travelled from Liberia, the hardest-hit nation in the current outbreak.

"The fact that Mr Duncan had travelled to Africa was not communicated effectively among the care team, though it was in his medical chart," the hospital said in its letter, which was signed by Texas Health CEO Barclay Berdan. "We did not correctly diagnose his symptoms as those of Ebola. For this, we are deeply sorry."

The letter added that the facility "did not live up to the high standards that are the heart of our hospital's history, mission and commitment".

Two nurses, Nina Pham and Amber Vinson, who cared for Duncan are now fighting the disease. The hospital said it was looking into how they became infected, despite their compliance with equipment and safety procedures.

The women are currently hospitalised in Atlanta, Georgia and Bethesda, Maryland.

Speaking on ABC's Sunday morning news show, the head of the National Institute for Allergy and Infectious Diseases, Anthony Fauci, said US health authorities were implementing new procedures for health care workers treating Ebola patients, including ensuring that no skin is exposed at all.

Ebola has killed more than 4,500 people in an outbreak centred in West Africa.