The ambulance which carried Thomas Eric Duncan, who suffered from Ebola.

DALLAS — 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 hospital cited the man’s privacy as the reason for not identifying him. However, Gee Melish, who said he was a family friend, identified the man in Texas infected with Ebola 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 after he traveled to the United States from Liberia in late September. The children had gone to school early this week but have since been sent home and are being monitored for symptoms.

The Dallas Ebola case 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 was 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.

The patient had initially sought treatment at Texas Health Presbyterian Hospital late on 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 the Sudan. Osmanovic is from Bosnia.

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.”

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.

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.

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