Ashoko Mukpo, 33, was hired to work with Dr. Nancy Snyderman, NBC's chief medical editor and correspondent, who said he had a "low amount" of the virus in him.
Mukpo had only been working for them for 72 hours but had been in Liberia for two weeks prior to that, she said on Friday's Today show.
"My suspicion is he was infected before we met him," Snyderman said, adding that she intends to quarantine herself for 21 days after she returns to the U.S.
Reaching Out to 90 PeopleMeanwhile, officials are closely monitoring five children and up to 13 others who had contact with the first Ebola patient diagnosed in the U.S. while he was symptomatic. They are also reaching out to another 90 or so that may have had direct contact with him or someone close to him, officials say.
The infected man, identified as Thomas Eric Duncan, remains in the hospital while his family is being quarantined and the apartment cleaned due to "hygiene" issues, Dallas County Judge Clay Jenkins said Thursday.
Law enforcement officers were stationed outside the northeast Dallas apartment where Duncan, who is in his mid-40s and a resident of Monrovia, Liberia, had been staying with relatives when he fell ill, according to the Dallas Morning News.
Among those also being monitored are three members of the ambulance crew who assisted Duncan and tested negative for the virus, but are restricted to their homes while their conditions are observed.
Children Being Kept from SchoolThe five children, who attend four separate schools, apparently had contact with the man over the weekend and then returned to classes this week. They are currently being told to stay home from school, the Dallas Independent School District said in a statement Wednesday.
"Since the students are not presenting any symptoms there is nothing to suggest that the disease was spread to others, including staff," the statement said.
Still, parents were worried, with some saying they planned to keep their children home, according to News.
In addition, The New York Times reported that Duncan had "direct contact" with a pregnant neighbor in Liberia who had Ebola shortly before he came to the U.S.
On Thursday, after the Associated Press obtained Duncan's pre-boarding questionnaire in which he said he'd had no contact with anyone with Ebola, Liberian officials told the Associated Press Duncan would be prosecuted for lying on this form.
Duncan initially went to a Dallas emergency room last week, but was sent home, despite telling a nurse that he had been in disease-ravaged West Africa, the hospital acknowledged Wednesday.
Duncan's answer "was not fully communicated" throughout the hospital's medical team, Dr. Mark Lester, who works for the hospital's parent company, told the Associated Press.
His nephew, Josephus Weeks, 42, of Kannapolis, North Carolina, told the Today show Thursday he's the one who had to call the CDC after the hospital sent his uncle home.
"I was concerned for his life," he said. "He wasn't getting the appropriate care and I feared others might get affected if he wasn't taken care of."
A day after Duncan's diagnosis was confirmed, a nine-member team of federal health officials was tracking anyone who had close contact with him.
The team from the Centers for Disease Control and Prevention was in Dallas to work with local and state health agencies to ensure that those people are watched every day for 21 days.
"If anyone develops fever, we'll immediately isolate them to stop the chain of transmission," Dr. Tom Frieden, director of the Atlanta-based Centers for Disease Control and Prevention, said.
Duncan has been kept in isolation at the hospital since Sunday. He was listed in serious but stable condition.
Ebola is believed to have sickened more than 7,100 people in West Africa, and more than 3,300 deaths have been linked to the disease, according to the World Health Organization.
Officials said there are no other suspected cases in Texas, but the diagnosis sent anxiety through the area's West African community, whose leaders urged caution to prevent spreading the virus.
Below are answers to questions about Ebola and the Texas case from the CDC and an expert from UCLA:
Will there be an epidemic here in the United States?
"I think there is no cause for concern," Anne Rimoin, an associate professor in epidemiology at UCLA's School of Public Health. "We know how the Ebola virus is transmitted and it is not easily transmitted from person to person, in particular people who are not symptomatic."
How does Ebola spread?
"You really only get through it direct contact with bodily fluids," says Rimoin. "The reality of it is is that until someone is showing symptoms they can't transmit the virus to anyone else and when they do start to show symptoms it comes on very hard and very fast. They're not likely to be wandering around and interacting with lots of people."
So who's at risk?
Texas health officials already have begun tracking down those who had close and peripheral contact with Duncan.
Could Ebola have spread on the airplane?
No, Frieden said, because the man wasn't sick then. The CDC said there is no need to monitor anyone else on those flights.
How will this patient be treated?
Good hydration and IV nutrition have proven to be key for those other patients. Frieden said the hospital was discussing experimental treatments. A Tekmira Pharmaceuticals drug called TKM-Ebola and blood transfusions from an Ebola survivor were given to one of the recently infected U.S. aid workers.
Could there be more travelers with Ebola?
No one's ruling it out. People boarding planes in the outbreak zone are checked for fever, but that does not guarantee that an infected person won't get through.
For more information on Ebola, go to www.cdc.gov/vhf/ebola/.
With reporting by ASSOCIATED PRESS and CAITLIN KEATING