First Ebola Case in US, But CDC Vows 'We Will Stop It Here' Patient left Liberia on Sept. 19 and became sick on Sept. 17.

 -- The first Ebola case has been diagnosed in the United States, but a top health official said today there is "no doubt... we will stop it here."

Dr. Tom Frieden, the director of the Centers for Disease Control and Prevention, said the patient left Liberia on Sept 19 and arrived in the U.S. on Sept. 20. The patient sought medical help on Sept. 27 and was put in isolation on Sept. 28, Frieden said.

Tests confirming the Ebola diagnosis came back today. The White House said President Obama was briefed about the patient by Frieden.

Frieden stressed that the patient was not sick on departure from Liberia or upon arrival in the U.S. and 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.

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He later added that Ebola is a "scary disease," but vowed, "We are stopping it in its tracks in this country."

Although American Ebola patients have been treated in the United States prior to this diagnosis, they all contracted Ebola in West Africa. Ebola has killed 2,917 people and infected 3,346 others since the outbreak began in March.

Frieden declined to identify the patient other than to say, "The individual was here to visit family who live in this country." Frieden later indicated the patient was male when he modified the comment to say, "He was visiting family members and staying with family members who live in this country."

Health officials are tracking down the patient's close contacts to determine whether they contracted the virus, Frieden said.

The Dallas Fire Rescue EMS crew that transported the patient have been quarantined according to CDC and Dallas County Health guidelines, city officials announced Tuesday evening.

The city activated its Emergency Operations Center and is on Level 2: High Readiness.

Dr. Edward Goodman, head epidemiologist at the Texas Health Presbyterian Hospital Dallas, said he could not reveal information about the patient's symptoms or treatment, but said that "he is ill and he is under intensive care."

Frieden said possible experimental therapies are being discussed with the family and may be announced later.

Ebola is spread via contact with bodily fluids, such as blood and urine, but it is not contagious unless Ebola symptoms are present, the state health department said. Symptoms can take between two and 21 days to appear after exposure to the virus, according to the CDC.

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This has been the worst Ebola outbreak since the virus was discovered in 1976. More people have died from Ebola since March than in every other Ebola outbreak to date combined, according to data from the World Health Organization.

Last week, the CDC released a report saying that without the proper intervention, the Ebola outbreak could reach 1.4 million cases by the end of January. But if 70 percent of Ebola patients are placed in Ebola treatment centers or home settings that reduce transmission by December, the outbreak could be nearly over by the end of January, according to the CDC. Every month intervention is delayed means more cases and a slower stop to the outbreak.

Editor's Note: An earlier version of this story said the patient left Liberia on Sept. 10. The patient left on Sept. 19.