(CNN) -- A nurse asked the U.S. Ebola patient for his travel history while he was in an emergency room, and the patient volunteered that he had traveled to Africa, said Dr. Mark Lester, executive vice president of Texas Health Resources. But that information was not "fully communicated" to the medical team, he says.
Some school-age children have been in contact with the Ebola patient being treated in Dallas, Texas Gov. Rick Perry said Wednesday. They have been identified and are being monitored for symptoms, he said.
[Original story published 12:54 p.m. ET]
It's a lapse that has Americans concerned and health officials asking how it could happen.
A man who had the deadly Ebola virus -- but didn't yet know it -- walked into a Dallas emergency room September 26. Although his symptoms could have indicated Ebola, among other diseases, no one at the hospital asked him if he had recently traveled to countries where the virus is present, a source close to the case told CNN.
The man, who had just flown from Liberia to the United States, didn't offer the information either, the source said, and he then left the hospital. A spokesman for Texas Health Presbyterian Hospital says it's investigating whether the patient was questioned about his travels.
Regardless, two days later, on September 28, the man returned to the facility, where it was determined he likely had Ebola and was isolated. He tested positive for the Tuesday, health officials said.
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The Centers for Disease Control and Prevention, which has helped lead the international response to Ebola, advises that all medical facilities should ask patients with symptoms consistent with Ebola for their travel history.
It's possible others were infected because of the lapse. People who have Ebola are contagious -- but only through contact with infected bodily fluids -- when they display active symptoms of the virus, such as a high fever, severe headache, diarrhea and vomiting, among others. It's not like a cold or the flu, which can be spread before symptoms show up, and it doesn't spread through the air.
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That the man had recently arrived in the United States from Liberia should have been a huge red flag, if he was asked about his travels. Liberia is one of the hotspots in a large outbreak of Ebola in West Africa, with 3,458 cases and 1,830 deaths as of September 23, according to the World Health Organization. Other countries affected include Guinea, Nigeria and Sierra Leone. In total, more than 3,000 people have died in those countries from Ebola, and more than 6,500 have contracted the disease.
This summer, two American missionaries who were working in Liberia contracted the virus and were brought back to the United States, where they were treated with the experimental drug ZMapp. Another American doctor working with the same charity was also infected in Liberia and brought home for treatement. They all have since recovered from the virus and were released from care.
The CDC has ramped up a national effort to stem the spread of Ebola, and in September President Barack Obama spoke at CDC headquarters in Atlanta. He called the virus a global health and security threat, and pledged U.S. assistance to the affected countries to try to stem the tide of the disease.
Ebola patient in serious condition
The patient in Dallas is now under intensive care and isolated at Texas Health Presbyterian Hospital, said CDC Director Dr. Thomas Frieden.
He is in serious condition, the hospital told CNN Wednesday.
The man flew from Liberia and arrived in Dallas to visit family on September 20, Frieden explained. He started feeling ill around September 24 and sought medical care on September 26, he added.
CNN Chief Medical Correspondent Dr. Sanjay Gupta asked Frieden Wednesday on "New Day" if the man should have been tested for Ebola on his first visit to the hospital, and if he should have been asked about his recent travel history.
"That's one of the things we'll be looking at," Frieden said. "But we're reiterating the message for every health worker in this country -- think about travel history. If someone's been in West Africa within 21 days and they've got a fever, immediately isolate them and get them tested for Ebola."
Gupta then asked Frieden to explain guidance the CDC has issued on that and again asked: "Should this person have been tested?"
"We weren't there so I can't tell you exactly what that person said..." Frieden responded.
Gupta interjected, "You're advising public health departments. Last time I was here (at the Centers for Disease Control and Prevention in Atlanta) there was a call with many primary care doctors to educate them on this exact issue. That was a couple of months ago. Should this person have been tested?"
Frieden answered, "We know that in busy emergency departments all over the country, people may not ask travel histories. I don't know if that was done here. But we need to make sure that it is done going forward."
Air travel testing
Every person who travels by air is screened before departure and at arrival in Liberia, Guinea and Sierra Leone, but because the man says he began feeling ill days after landing in the United States, a screening test in West Africa would likely have not turned up that he had Ebola.
However, it's unclear what kind of screening someone flying from West Africa might receive when they land in the United States, said CNN's Senior Medical Correspondent Elizabeth Cohen. She and her crew recently reported in and flew from West Africa, where she said they were screened numerous times for Ebola by having their temperatures taken at the airport.
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Should we worry?
But when they arrived back in the United States, and asked travel officials about whether their temperatures would be taken or if they'd be screened for Ebola, they were given unclear explanations about how the process worked and ultimately were not tested.
Regardless, the CDC maintains that passengers on the Texas man's plane were likely not at risk because the man was not displaying active symptoms on the flight.
Frieden explained that people who have Ebola are not able to spread the disease unless they are symptomatic.
Paramedics who transported the patient to the hospital have been isolated, Dallas Mayor Mike Rawlings' chief of staff said. They have not shown symptoms of the disease so far, Frieden said.
The ambulance used to carry the patient was still in use for two days after the transport, city of Dallas spokeswoman Sana Syed said.
But she emphasized that the paramedics decontaminated the ambulance, as they do after every transport, according to national standards.
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Finding the people the man came into contact with
During the time he was symptomatic, the man did have a handful of contacts with people, Frieden said.
A CDC team headed to Dallas to help investigate those contacts.
Once those people are identified, they will be monitored for 21 days -- taking their temperatures twice a day -- in cooperation with local and state health officials, Frieden said Wednesday.
But Gupta pointed out that the people identified as contacts aren't, as protocol, quarantined unless they are symptomatic.
"We don't want to isolate parts of the world, or people who aren't sick," Frieden said, "because that's going to drive people underground and make it harder to contain this outbreak."
CNN's AnneClaire Stapleton, Jason Morris, Chandler Friedman, Greg Botelho and Ed Payne contributed to this report.