The condition of the lone Ebola patient to be diagnosed in the US has worsened and is now deemed critical, according to the Dallas hospital that has been treating him.

Texas Health Presbyterian Hospital Dallas, where Thomas Eric Duncan is being treated, did not provide any further details on Saturday about his condition, and Candace White, a hospital spokeswoman, did not immediately respond to emails and phone calls.

The hospital previously said Duncan was being kept in isolation and that his condition was serious but stable.

Duncan travelled from Ebola-hit Liberia to Dallas on September 20 before he began showing symptoms of the disease.

After an initial visit to the emergency room at Texas Health Presbyterian Hospital, he was sent home, even though he told a nurse he had been in West Africa.

He returned to the hospital two days later, last Sunday, and has been kept in isolation since then.

Flaw in health records

Texas Health Presbyterian Hospital Dallas issued a news release late on Friday saying that the doctor who initially treated Duncan did have access to his travel history, after all.

It had said on Thursday that a flaw in the electronic health-records systems led to separate physician and nursing workflows, and that the doctor had not had access to Duncan's travel history.

Wendell Watson, the hospital spokesman, said on Saturday he could provide no further details, adding: "We're still looking into the entire chain of events."

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US health officials say they are monitoring about 50 people who may have had contact with Duncan for signs of the deadly disease.

Among those are nine people who are believed to be at a higher risk. Thus far, none have shown symptoms.

Included in the group are those people who later rode in the ambulance that took Duncan to the hospital last Sunday, according to Dr Tom Frieden, director of the Centres for Disease Control and Prevention (CDC).

A hazardous-materials crew decontaminated on Friday the Dallas apartment where Duncan was staying when he got sick during his visit.

The materials were sealed in industrial barrels that were to be stored in lorries until they can be hauled away for permanent disposal.

The family who lived there was moved to a private home in a gated community, where they are being carefully monitored.

The city had been having trouble finding a place that would take in Louise Troh, originally from Liberia, her 13-year-old son and two nephews.

Isolation facilities

Four American aid workers who have become infected while volunteering in West Africa have been treated in special isolation facilities in hospitals in Atlanta and Nebraska, and a US doctor exposed to the virus in Sierra Leone is under observation in a similar facility at the National Institutes of Health.

Ebola is not contagious until symptoms begin, and according to the CDC, Ebola symptoms can include fever, muscle pain, vomiting and bleeding, and can appear as long as 21 days after exposure to the virus.

The virus that causes Ebola is not airborne and can only be spread through direct contact with the bodily fluids - blood, sweat, vomit, faeces, urine, saliva or semen - of an infected person who is showing symptoms.

US health officials have been preparing since summer in case an individual traveller arrived there unknowingly infected, telling hospitals what infection-control steps to take to prevent the virus from spreading in health facilities.

People boarding planes in the outbreak zone are checked for fever, but may not yet have shown symptoms.

The first Ebola diagnosis in the US has raised concerns about whether the disease that has killed about 3,400 people in West Africa could spread in the US.

Federal health officials say they are confident they can keep it in check.

Source: Agencies