ATLANTA -- In this age of modern air travel, it was just a matter of when, not if.
A man at a Dallas hospital is the first person diagnosed with Ebola in the United States. Now, health officials are searching for people who came in contact with the man.
Ebola is spread by direct contact with the bodily fluids of someone actively sick with the virus. 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.
But while health officials try to calm concerns about the disease spreading in the United States, they say they're leaving nothing to chance.
Isolating the patient and paramedics
The patient is now under intensive care and isolated at Texas Health Presbyterian Hospital, said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention.
The man flew from Liberia -- one of the Ebola hotspots in West Africa -- and arrived in Dallas to visit family on September 20, Frieden explained.
He started feeling ill about four days after arriving. 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 U.S., 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 arriving from West Africa might receive when they arrive in the United States, said 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.
But when they arrived back in the United States, and asked travel officials about whether their temperatures would be taken or they'd receive screening 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.
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 stressed that the paramedics decontaminated the ambulance, as they do after every transport, according to national standards.
Patient goes to hospital but wasn't tested for Ebola
The patient started feeling ill around September 24 and sought medical care on September 26, Frieden said. During that visit, the man did not say anything about his recent travel to West Africa and Texas Health Presbyterian Hospital did not ask about his travel history, an official familiar with the case said.
CNN has asked the hospital for comment but has not yet gotten a response.
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," Gupta continued. "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."
Finding the people the man came into contact with
Two days after he initially sought medical care and was sent home from the hospital, the man went back to Texas Health Presbyterian Hospital and was isolated, the CDC said.
During the time he was symptomatic, the man had 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.
Frieden explained that people who have Ebola are not able to spread the disease 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."