Two days after he was sent home from a Dallas hospital, the man who is the first person to be diagnosed with Ebola in the United States was seen vomiting on the ground outside an apartment complex as he was bundled into an ambulance.

The Dallas Ebola case, involving a man who flew back to the United States last month from Liberia, has prompted national concern over the potential for a wider spread of the deadly virus from West Africa, where at least 3,338 people have died in the worst outbreak on record.

U.S. health officials have said the country's healthcare system is well prepared to contain any spread of Ebola through careful tracking of people who had contact with the patient and appropriate care for those admitted to hospital.

"His whole family was screaming. He got outside and he was throwing up all over the place," resident Mesud Osmanovic, 21, said on Wednesday, describing the chaotic scene before the man was admitted to Texas Health Presbyterian Hospital on Sunday where he is in serious condition.

The hospital cited the stricken man's privacy as the reason for not identifying him. However, Gee Melish, who said he was a family friend, identified the man as Thomas Eric Duncan.

The New York Times said that Duncan, in his mid-40s, helped transport a pregnant woman suffering from Ebola to a hospital in Liberia, where she was turned away for lack of space. Duncan helped bring the woman back to her family's home and carried her into the house, where she later died, the newspaper reported.

Four days later Duncan left for the United States, the Times said, citing the woman's parents and neighbors.

Texas health officials said that up to 18 people, including five children, had contact with the Ebola patient since he returned to the United States in late September. The children had gone to school early this week but have since been sent home and are being monitored for symptoms.

Ebola spreads through contact with bodily fluids such as blood or saliva, which health experts say limits its potential to infect others, unlike airborne diseases.

Still, the long window of time before patients exhibit signs of infection, such as fever, vomiting and diarrhea, means an infected person can travel without detection.

Airline and hotel company shares dropped sharply on U.S. markets on Wednesday over concerns that Ebola's spread outside Africa might curtail travel.

Drugmakers with experimental Ebola treatments in the pipeline saw their shares rise.

SENT HOME

The Dallas patient had initially sought treatment at Texas Health Presbyterian Hospital late last Thursday and was sent home with antibiotics rather than being observed further, even though he told a nurse he had recently returned from West Africa. By Sunday, he needed an ambulance to return to the same hospital, where he was admitted.

A nurse asked about the travel as part of a triage checklist and was told about it. “Regretfully, that information was not fully communicated throughout the full teams. As a result, the full import of that information wasn’t factored into the full decision making,” Texas hospital official Mark Lester said.

Infectious disease experts said that time gap represented a critical missed opportunity that may have led others to be exposed to the virus.

At the apartment complex, Osmanovic said he met the man three times over the years when he was visiting his family. Most of the neighborhood is from Liberia, Somalia or Sudan. Osmanovic is from Bosnia.

The only sign on Wednesday of the family's presence was someone occasionally pulling back the white blinds to peek out into the parking lot. A security officer blocked the entrance to the complex, with instructions only to let residents in and out.

Dr. Christopher Perkins, Dallas County Health and Human Services Medical Director, said that of the 18 people who had been in contact, many were "close family members".

The children among them "did not have any symptoms and so the odds of them passing on any sort of virus is very low", said Mike Miles, Dallas Independent School District superintendent.

Miles said the four different schools they attended would be staffed with additional health professionals and classes would remain in session.

Texas officials said health workers who took care of the patient had so far tested negative for the virus and there were no other suspected cases in the state. Texas Governor Rick Perry told a news conference he was confident the virus would be contained, as did other officials.

While past outbreaks of Ebola killed as many as 90 percent of victims, the current epidemic's fatality rate has averaged about 50 percent in West Africa.

The patient arrived in Texas on Sept. 20, and first sought treatment six days later, according to the U.S. Centers for Disease Control. The Liberian government said that the man showed no signs of fever or other symptoms of Ebola when he left the country on Sept. 19.

A Liberian official said the man traveled through Brussels to the United States. United Airlines said in a statement that the man took one of its flights from Brussels to Washington Dulles Airport, where he changed planes to travel to Dallas-Fort Worth.

A spokesman for Brussels Airlines, the only airline to fly direct scheduled services between Brussels and Monrovia, said he could not confirm that the passenger had flown with the company.

"We also have not been contacted by anyone to tell us to take measures or contact passengers because of an infected passenger traveling with us," spokesman Geert Sciot said.

Separately on Wednesday, citing a "heightened sense of awareness of Ebola", the Queens Medical Center in Honolulu, Hawaii, said it was treating a patient in isolation.

"At this time the patient's history and clinical presentation do not appear to be consistent with Ebola and the patient may be diagnosed with a number of conditions other than Ebola," the statement said.