A team of federal health officials was on Wednesday still tracking down anyone who had close contact with the Ebola patient after he fell ill on September 24.

The group of 12 to 18 people identified so far included three members of the ambulance crew that took the man - named as Thomas Eric Duncan - to the hospital, as well as a handful of schoolchildren. Those identified were to be isolated and monitored over three weeks.

"That's how we're going to break the chain of transmission, and that's where our focus has to be," Dr. Tom Frieden, Director of the Centers for Disease Control and Prevention, told the AP news agency on Wednesday. "If anyone develops fever, we'll immediately isolate them to stop the chain of transmission."

It was revealed on Wednesday that Duncan - the first patient diagnosed with Ebola in the US - had visited a Dallas emergency room, but was sent home - despite telling a nurse he had recently visited the disease-hit country of Liberia.

Vomited outside apartment

Two days after that, the man was seen vomiting on the ground outside an apartment complex and was bundled into an ambulance.

Details of Duncan's 28-hour trip from West Africa emerged on Wednesday, revealing that he flew on two airlines and took three flights involving long layovers. After leaving Monrovia, Liberia, Duncan flew to the Belgian capital Brussels and on to Dulles International Airport near Washington, before arriving in Dallas on September 20.

Dr Anthony Fauci, director of the National Institutes of Allergy and Infectious Disease at the National Institutes of Health said he believed it was "extraordinarily unlikely" that anyone else had been infected during the journey, given that the patient himself had not become ill - and therefore infectious - at the time.

The Ebola death toll in West Africa was said to have soared to 3,338 with the virus killing almost half of the more than 7,000 people it has infected, according to World Health Organization figures released Wednesday. The United Nations has been accused of an inadequate response to the outbreak of the disease in Liberia, Guinea and Sierra Leone.

rc/av (AFP AP, Reuters)