The CDC has confirmed the first Ebola case diagnosed in the United States.

CDC Director Tom Frieden said the patient had traveled from Liberia, where he contracted the virus, leaving the country on Sept. 19 and arriving in the U.S. on Sept. 20 by plane. He showed no signs of the disease while traveling, Frieden said. Symptoms began to show on Sept. 24, and he's now "critically ill" at the Texas Health Presbyterian Hospital in Dallas.

Frieden said several times that an asymptomatic patient is not contagious, making the risk to fellow airline passengers extremely low. "Ebola doesn't spread before a patient gets sick, and he didn't get sick until four days after he got off the plane," he said.

Texas Health Presbyterian Hospital in Dallas, Tuesday, Sept. 30, 2014, where a patient is showing signs of the Ebola virus and is being kept in strict isolation. Image: LM Otero/Associated Press

The CDC director said Tuesday afternoon that the next steps involve caring for the patient, providing "the most effective care possibly as safely as possible," keeping him isolated and identifying "all people who may have had contact w/ the patient while he could have been infectious."

"This is core public health work," Frieden said of isolating the patient and preventing transmission.

"The bottom-line here is that I have no doubt that we will control this case of Ebola so that it does not spread widely in this country," CDC Director Tom Frieden 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."

The Texas Department of State Health Services confirmed the news in a statement Tuesday afternoon.

"A Texas hospital patient has tested positive for Ebola, making the patient the first case diagnosed in the United States. The test was conducted at the state public health laboratory in Austin. The Centers for Disease Control and Prevention confirmed the positive result," the Texas Department of State Health Services said in the statement:

The patient is an adult with a recent history of travel to West Africa. The patient developed symptoms days after returning to Texas from West Africa and was admitted into isolation on Sunday at Texas Health Presbyterian Hospital in Dallas. The Texas Department of State Health Services is working with the CDC, the local health department and the hospital to investigate the case and work to prevent transmission of the disease. The hospital has implemented infection control measures to help ensure the safety of patients and staff.

Dallas County Health and Human Services director Zachary Thompson said the North Texas public should be aware about Ebola, stating, "With what we’ve seen in the media and how deadly the Ebola virus is, it is a concern."

This is the first patient diagnosed with this strain of Ebola anywhere outside of Africa, not just in the U.S., according to the CDC director. At least three previously known Ebola patients — all diagnosed in Africa — have been flown to and treated in U.S. hospitals this year.

The virus is not spread through the air, making it far less contagious than the flu and less of a danger to air travelers. Instead, it is spread by contact with bodily fluids.

Here's how the CDC explains its spread:

Ebola is spread through direct contact (through broken skin or mucous membranes) with blood or body fluids (including but not limited to urine, saliva, feces, vomit, and semen) of a person who is sick with Ebola objects (like needles and syringes) that have been contaminated with the virus infected animals. Ebola is not spread through the air or by water, or in general, food. However, in Africa, Ebola may be spread as a result of handling bushmeat (wild animals hunted for food) and contact with infected bats.

More than 6,500 cases of Ebola have been reported in three western Africa countries — Liberia, Guinea and Sierra Leone — since the beginning of this year's outbreak, the WHO said earlier on Tuesday. Over 3,000 people have died.

"Ebola is a scary disease because of the severity of the illness it causes," Frieden said Tuesday evening. "We're stopping it in its tracks in this country."

Megan Specia contributed to this report.