Four people close to the first person diagnosed with Ebola in the US have been quarantined in a Dallas apartment as health officials widen their search for people who had direct or indirect contact with him.

US health officials said on Thursday that 12 to 18 people had direct contact with the patient, who flew to Texas from Liberia via Brussels and Washington DC two weeks ago, and they in turn had contact with scores of others.

Up to 100 people have been contacted and a handful are being monitored, according to Dr Thomas Frieden, director of the US Centres for Disease Control and Prevention (CDC).

None of those thought to have had contact with the patient were showing symptoms of Ebola, Dallas County officials said.

The man had been staying in a Dallas apartment, where quarantine is being implemented.

He stayed there for about a week before going to a Dallas hospital, according to health authorities.

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"The sheets were placed in a sealed plastic bag and have been in the bag, as well as the belongings of [the patient], those were also in a bag," Clay Jenkins, Dallas county's top political official, said.

In Liberia, Binyah Kesselly, the head of the country's airport authority, said the government could prosecute the man for denying he had contact with someone who was eventually diagnosed with Ebola.

The government said he had failed to declare that he helped a neighbour after she fell critically ill on September 15 and died in days after that.

The Texas hospital, where the man is being treated, had announced a day earlier that the patient's symptoms and recent travel indicated a case of Ebola, the virus that has killed more than 3,000 people across West Africa and infected a handful of Americans who have travelled to that region.

"The infected person came from Liberia on September 19 and began to develop symptoms on September 24. He first sought care on the 26th of September and on the 28th was admitted in Texas," Frieden said.

Isolation facilities

The CDC has said 12 other people in the US have been tested for Ebola since July 27. Those tests came back negative.

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.

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.

US health officials have been preparing since summer in case an individual traveller arrived here 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.

Ebola is not contagious until symptoms begin, and it takes close contact with bodily fluids to spread.

Source: Agencies