The Centers for Disease Control and Prevention confirmed on Tuesday the first case of Ebola diagnosed in the United States.

“An individual traveling from Liberia has been diagnosed with Ebola in the United States,” Thomas Frieden, director of the CDC, said in a news conference Tuesday afternoon.

State and federal health officials announcing the confirmed case repeatedly stressed the difficulties of contracting Ebola, which can be spread through bodily fluids or infected animals but not through the air or by water.

This person who is infected left Liberia on Sept. 19 and arrived in the U.S. the following day to visit family in this country. The person, who was not identified, had no symptoms at the time and began showing symptoms about four days after arriving in the U.S.

“The bottom line here is that I have no doubt that we will control this importation, or this case of Ebola, so that it does not spread widely in this country,” he said. “It is certainly possible that someone who had contact with this individual could develop Ebola in the coming weeks. But there is no doubt in my mind that we will stop it here.”

This is the first time Ebola has been diagnosed in the U.S. and the first time someone was diagnosed with this particular strain outside of Africa, he said. Still, health officials expressed optimism going forward.

“We’re stopping it in its tracks in this country,” Frieden said.

The patient with Ebola is being treated in intensive care, according to Edward Goodman, the hospital epidemiologist at Texas Health Presbyterian Hospital Dallas

The man sought medical care on Sept. 26, but was sent home. He was admitted to the hospital two days later and placed into isolation.

Health officials are going to work to identify everyone who may have been exposed to this patient, Frieden said. This group, described as a “handful” of people by Frieden, will be watched for three weeks to see if any symptoms emerge.

People who traveled on the flight with this man are not in danger because the patient was not symptomatic at the time. Frieden said the man’s temperature was checked before departing on the plane.

“There is zero risk of transmission on the flight,” Frieden said.

Frieden declined to say if the person with Ebola is a U.S. citizen. This man was visiting and staying with family members, he said. He is not believed to have been involved in the Ebola response, Frieden said.

“Remember, Ebola does not spread from someone who’s not infectious,” said Frieden, who has visited the West African region ravaged by Ebola. “It does not spread from someone who does not have a fever or other symptoms.”

David Lakey, head of the Texas Department of Health Services, said the state’s laboratory in Austin, Tex., was certified last month to do Ebola testing. That laboratory received a blood sample from the patient on Tuesday morning and confirmed it was Ebola shortly after 1 p.m., he said.

The Texas Department of Health Services said that the patient is at Texas Health Presbyterian Hospital in Dallas.

The test, the Texas health department said, was conducted at the state public health laboratory in Austin and later confirmed by the CDC.

The CDC recommends that individuals protect themselves by avoiding contact with the blood and body fluids of people who are ill with Ebola. DSHS also encourages health care providers to ask patients about recent travel and consider Ebola in patients with fever and a history of travel to Sierra Leone, Guinea, Liberia, and some parts of Nigeria within 21 days of the onset of symptoms.

The deadliest Ebola outbreak in history is centered in the West African countries of Liberia, Sierra Leone and Guinea, where it has killed more than 3,000 people and infected thousands of others. There is a separate outbreak in Congo.