The first Ebola case has been diagnosed in the United States, the Centers for Disease Control and Prevention announced today.

The person who first tested positive for Ebola is a patient at Texas Health Presbyterian Hospital in Dallas, hospital spokesman Stephen O’Brien said Tuesday.

The unnamed person left Liberia on September 19 and arrived in the United States on September 20, Dr. Thomas Frieden, director of the CDC, told reporters Tuesday. At that time, the person did not have symptoms.

“But four or five days later” that person began to show symptoms, Frieden said. The patient was admitted into isolation on Sunday until the CDC could confirm the diagnosis.

CDC: People in contact with patient "could develop Ebola in coming weeks, but no doubt in my mind we will stop it…" pic.twitter.com/RqDZWSzXvL

— BuzzFeed News (@BuzzFeedNews) September 30, 2014

Frieden said the patient was not sick on departure from Liberia or upon arrival in the U.S., adding that the disease can only be contracted by someone exhibiting symptoms of the disease.

Frieden said he was confident there would not be an Ebola outbreak in the U.S.

“There is no doubt in my mind we will stop it here,” he said.

Several other Americans, including Dr. Kent Brantly and Nancy Writebol, were diagnosed in West Africa and then brought back to the United States for treatment. They have since recovered from the disease.

#Ebola transmits via contact with fluid from an infected victim – What you need to know: http://t.co/5oEz299hSf pic.twitter.com/liuRJKTJTf

— ABC News (@ABC) September 30, 2014

The Ebola outbreak has been centered in the West African countries of Guinea, Sierra Leone and Liberia, though there have been concerns about international air travel and other factors may contribute to its spread. Another concern is that symptoms do not appear until two to 21 days after being infected.

NOW LIVE: CDC news conference on first U.S. Ebola case http://t.co/KOcTNPTqLr pic.twitter.com/FbAgdzBd95

— NBC News (@NBCNews) September 30, 2014

According to last week’s World Health Organization report, more than 3,000 people in West Africa have died after being infected with Ebola and there have been 6,553 cases of the virus overall, though that number is likely higher due to difficulties in tracking and reporting the disease.

COMING UP: The CDC discusses first confirmed case of Ebola in the U.S. Watch live here: http://t.co/2KOIkgo4Vg pic.twitter.com/eF99pVmsng

— NBC News (@NBCNews) September 30, 2014

According to the CDC, Ebola causes viral hemorrhagic fever. Early symptoms may include sudden onset of fever, weakness, muscle pain, headaches and a sore throat.