Questions mounted Wednesday over why US doctors failed to immediately identify a patient who sought care for symptoms of Ebola, exposing others for four full days before he was isolated.
The first diagnosed case outside Africa has raised alarm about the spread of the deadly virus, which has killed more than 3,000 people and infected more than 6,500 in five countries since the start of the year.
The man, whose identity and nationality have not been released, had recently traveled from Liberia, a nation at the center of West Africa's deadly Ebola outbreak, to Texas in order to visit members of his family.
He left Liberia on September 19, arrived in Texas a day later and did not exhibit symptoms until September 24, Centers for Disease Control and Prevention chief Tom Frieden said Tuesday.
He sought medical care on the 26th, and was sent home. He was returned via ambulance to the Texas Health Presbyterian Hospital Dallas on September 28, and was placed in strict isolation.
Anthony Fauci, the head of the National Institute for Allergy and Infectious Disease, said the man should have been identified as a suspected Ebola case on the 26th.
"If the ER physician had asked for a travel history, (and said), 'Do you have any recent travel outside of the country?' And if the person said, 'Well, I just came back from Liberia,' that would have been an enormous red flag for anybody, given the publicity that we have," Fauci said on CNN.
"So that is really the issue, to make sure physicians are aware that we have a problem, that there is an outbreak in West Africa and people will be coming to the United States who will be without symptoms."
Early Wednesday, the hospital said in a brief statement that the man was "currently listed in serious condition."
Meanwhile, Zachary Thompson, the director of Dallas County Health and Human Services, told local media WFAA "there may be another case that is a close associate with this particular patient."
The incubation period for Ebola is between two and 21 days. Patients are not contagious until they start to show signs of fever, aches, vomiting and diarrhea.
Three crew members who worked in the ambulance that transported the patient have tested negative for Ebola, but they will be monitored for 21 days, the City Of Dallas said on Twitter.
The man is believed to have been infected in West Africa, where the world's largest outbreak of Ebola has taken more than 3,000 lives since the beginning of the year.
Frieden said there was "zero risk" that the man had infected others on the plane, but that a "handful" of people may have been exposed to him while he was sick in Texas.
Those contacts are being tracked and will be monitored for three weeks to see if they begin to exhibit symptoms of Ebola.
In announcing the United States' first diagnosed case of Ebola, Frieden stressed that the nation was prepared and would be able to stop the deadly virus from spreading.
"Most hospitals have been prepared for several weeks now," said Debra Spicehandler, infectious disease expert at Northern Westchester Hospital.
The high-profile cases of three American missionaries who were infected with Ebola while treating patients in Liberia and were evacuated to US hospitals, where they recovered, have helped raised awareness of proper protocols, she said.
However, Jesse Goodman, professor of medicine at Georgetown University Medical Center, said the early steps taken in Texas indicate some gaps in the US medical system's preparedness for Ebola's spillover from West Africa.
"While much of the response so far seems exemplary, we don't know why the disease was not recognized when he first sought care," Goodman said.
"We don't know if a travel history, one of our most basic but important diagnostic tools, was obtained and testing considered then."
While health experts say the public should not panic -- since Ebola is spread not through the air but only through close contact with the bodily fluids of an infected person -- medical personnel should be on the lookout for more cases of Ebola on US soil.
"It is critical for hospitals and health care workers everywhere to be sure they are alert, obtain travel histories," Goodman said.
"If there is any question at all it could be Ebola, contact CDC and, while sorting things out, act to isolate a sick patient returning from an epidemic area."