The Ebola virus Reuters

An unidentified man has contracted Ebola in the U.S. after visiting Liberia earlier this month. Until now, the only known cases of Ebola in the U.S. involved American doctors and aid workers who were infected while overseas and returned to the country for treatment.

The infected man left Liberia on Sept. 19 and came back home to Dallas, Texas, the following day to visit relatives. He became sick with symptoms days later, making this the first case of Ebola recorded in the U.S. There have been more than 6,500 reported cases of Ebola in Guinea, Liberia, and Sierra Leone as of Tuesday, and it has caused more than 3,000 deaths, according to the World Health Organization. Here's what you need to know Ebola in the U.S.:

When did the infected man seek treatment?

The infected man didn't develop symptoms until about four days after arriving in the U.S. He sought medical care on Friday but was sent home. He was admitted to the hospital two days later.

Did he infect people on the plane to Dallas?

Since the Ebola patient didn't show symptoms until days after arriving in Texas, the people he came into contact with on the flight and in the airport aren't at risk for the illness. One can only contract Ebola through direct contact with the bodily fluids of someone who's actively sick with with it.

Why wasn't he stopped at the airport?

Passengers on flights from hot zones in West Africa are screened once they land at a U.S. airport. Airport authorities look for symptoms of Ebola including vomiting, diarrhea, muscle pain, fever and unexplained bleeding. Since the Ebola patient didn't show symptoms until days after arriving in the U.S., authorities didn't stop him at the airport.

Did he affect others?

"It is certainly possible that someone who had contact with this individual ... could develop Ebola in the coming weeks,” Tom Frieden, director of the Centers for Disease Control and Prevention in Atlanta, said in at a news conference Tuesday, but added he that "there is no doubt in my mind that we will stop it here.”

Can he potentially infect others?

As the virus is only spread through direct contact, officials placed the infected man in quarantine quickly to prevent him from possibly infecting others, Thomas Geisbert, a professor of microbiology and immunology at the University of Texas Medical Branch at Galveston who studies viruses such as Ebola, said.

How many people did the patient encounter since falling ill?

It remains unclear who he came in contact with since he became contagious, Frieden said during the press conference. "We are just beginning the process; the investigation has just begun today. But the health department has already been very forward-leaning on that and already has locating information" for those contacts, Frieden continued. He stated it is just"a handful" of people, mostly family members.

How is the unidentified man being treated?

He's being treated in intensive care at Texas Health Presbyterian Hospital Dallas, according to Edward Goodman, the hospital’s epidemiologist. The ambulance he arrived in was later decontaminated, a Dallas official confirmed, and two paramedics and one paramedic intern are being monitored after transporting the patient to the hospital.