An individual who flew to the U.S. from Liberia earlier this month has been diagnosed with Ebola in Texas, the Centers for Disease Control and Prevention confirmed today. The case marks the first time the disease has been diagnosed in this country, although several infected health workers have been treated here after being diagnosed in Africa.

The patient was diagnosed at Texas Health Presbyterian Hospital in Dallas, and is being quarantined there, officials said in a press conference this afternoon. A team from the CDC is en route to Texas to help health officials there track anyone who might have had contact with the patient. Once those contacts are identified, they will be monitored for 21 days, the maximum time between exposure to the virus and the onset of symptoms. Anyone who develops a fever during that time will also be isolated. CDC director Thomas Frieden characterized the number of possible contacts as "a handful."

"I have no doubt we will stop this in its tracks in the U.S.," Frieden said. "But I also have no doubt that as long as the outbreak continues in Africa we will have to be on our guard."

There is little risk of the disease spreading widely in the U.S., Frieden said. Unlike highly contagious airborne pathogens like influenza, the Ebola virus requires contact with bodily fluids such as urine, saliva, feces, vomit, or semen to be transmitted. The risk is highest for people in direct contact with patients—typically healthcare workers and family members. In Africa, the lack of treatment centers and supplies has hampered efforts to contain the virus. But in the U.S., hospitals are better stocked and have better isolation facilities. In addition, public health officials have well-tested strategies to prevent the spread of infectious diseases. "This kind of contact tracing is core public health, it's what we do day in and day out," Frieden said.

A police car drives past the entrance to the Texas Health Presbyterian Hospital in Dallas, Tuesday, Sept. 30, 2014. A patient in the hospital is showing signs of the Ebola virus and is being kept in strict isolation with test results pending, hospital officials said Monday. LM Otero / AP

Due to privacy issues, no details about the gender, age, nationality, or condition of the individual were released, although several times officials referred to the patient as "he."

"I can say that he is ill, and he’s under intensive care," said David Goodman, hospital epidemiologist at Texas Health Presbyterian Hospital. Goodman declined to give any further details about the patient's treatment.

The patient came to the U.S. to visit family members who are citizens and was not known to be participating in any aid efforts for Ebola patients in Liberia before coming here, Frieden said. The patient left Liberia on a plane the 19th, arrived in the U.S. on the 20th, and became symptomatic on the 24th or 25th, Frieden said. The patient sought medical care on the 26th, but was not admitted to the hospital until the 28th. Asked about that discrepancy, Frieden noted that the symptoms of Ebola, which include fever, severe headache, and muscle pain overlap with symptoms of many other infections. He added that the CDC is urging physicians to ask patients with these symptoms about their travel history.

"It is certainly possible that someone who had contact with this individual, a family member or other individual, could develop Ebola in coming weeks, but there is no doubt in my mind we will stop it there," Frieden said.

Frieden downplayed the possibility of any danger to people who flew on the same flight. Ebola is only contagious in people who are symptomatic, and this individual was screened for fever before boarding the plane and did not become symptomatic until several days after the flight, Frieden said. "There is zero risk of transmission on the flight."

The current outbreak of Ebola in Africa is the worst in recorded history. As of yesterday it had infected a reported 6,574 people and killed 3,091, mostly in Guinea, Liberia, and Sierra Leone. A smaller outbreak in Nigeria appears to be contained, the CDC said earlier today.

There are no established treatments, although several experimental treatments are being rushed into production.