(Reuters) - U.S. health officials said on Tuesday the first patient infected with the deadly Ebola virus had been diagnosed in the country after flying from Liberia to Texas, in a new sign of how the outbreak ravaging West Africa can spread globally.

The patient sought treatment six days after arriving in Texas on Sept. 20, Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC), told reporters on Tuesday. He was admitted two days later to an isolation room at Texas Health Presbyterian Hospital in Dallas.

U.S. health officials and lawmakers have been bracing for the eventuality that a patient would arrive on U.S. shores undetected, testing the preparedness of the nation’s healthcare system.

Frieden said a handful of people, mostly family members, may have been exposed to the patient after he fell ill. He said there was likely no threat to any passengers who had traveled with the patient. Asked whether the patient was a U.S. citizen, Frieden described the person as a visitor to family in the country.

“It is certainly possible someone who had contact with this individual could develop Ebola in the coming weeks,” Frieden told a news conference. “I have no doubt we will stop this in its tracks in the United States.”

The Texas Department of State Health Services said it was working with the CDC, the local health department and the hospital “to investigate the case and help prevent transmission of the disease.”

“The hospital has implemented infection control measures to help ensure the safety of patients and staff,” the statement said.

U.S. hospitals have treated several patients who were diagnosed with Ebola in West Africa, the center of the worst known outbreak of the virus that has killed more than 3,000 people. The previous U.S. patients were all medical and other aid workers who were diagnosed while overseas and flown to the country in a specially outfitted airplane.

Frieden has said U.S. hospitals are well prepared to handle Ebola patients and has assured the public that the virus should not pose the same threat in the United States as it does in Africa.

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Ebola symptoms generally appear between two and 21 days after infection, meaning there is a significant window during which an infected person can escape detection, allowing them to travel. Frieden emphasized that Ebola cannot be spread through the air but only through contact with bodily fluids such as blood, diarrhea and tears.

He said that CDC and other health officials were discussing whether to treat the Ebola patient with an experimental drug for the virus, without specifying which one might be considered. Treatments from Mapp Biopharmaceutical and Tekmira Pharmaceuticals Corp have been used to treat a small number of patients so far in the outbreak.

Stocks in Tekmira and other small biotechnology companies working on Ebola therapies or vaccines rose on the news of the U.S. Ebola patient in after-hours trading.