Health authorities Tuesday confirmed the first case of Ebola diagnosed in the United States and identified the patient as a man who traveled on a commercial airliner to Texas from Liberia, a major hot spot in the growing West African epidemic.

The unnamed patient -- the first to bring the infection into the United States -- is in isolation and under intensive care at Texas Health Presbyterian Hospital in Dallas, health officials said yesterday. He is listed in critical condition. Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention, said the man could not spread the disease while in flight because he was not symptomatic.

Frieden said the patient left Liberia Sept. 19, arrived in the United States the next day and first showed symptoms on Sept. 24. He sought treatment at a Texas medical facility two days later but was sent home because his symptoms weren't serious enough to require hospitalization.

Two days later he returned and was hospitalized with symptoms of infection. Ebola can take up to three weeks to incubate.

His case has been confirmed through polymerase chain reaction -- PCR -- a highly sophisticated test that can definitively spot viral genes, Frieden said.

"This is the first case of Ebola diagnosed outside of Africa with this particular strain of Ebola," Frieden said, emphasizing that through the use of strict infection control techniques and key public health measures, such as identifying all contacts the patient had in recent days, the infection will not spread in this country.

"There is no doubt in my mind that we will stop it here," Frieden said.

The patient's flight information was not disclosed by either federal or Texas state health officials. Passengers he encountered are not being interviewed, officials said.

"There is zero risk of transmission on the flight," said Frieden, who added that this patient -- like all passengers leaving West Africa -- was scanned for fever.

The protocol involving this patient differs, however, from one followed by the CDC last spring when a symptomatic traveler arrived at Kennedy Airport from West Africa. CDC documents describe an all-out effort to re-trace the movements of the Minnesota resident who was found to be sick with Lassa fever contracted while traveling in West Africa.

Lassa fever, like Ebola, is a hemorrhagic viral disease endemic in West Africa. Lassa carries a high death rate but not at the level of Ebola.

Disease detectives fanned out in airports in both states searching for people the passenger might have encountered. Fellow airline passengers were also contacted.

Texas Health Commissioner David Lakey underscored that Ebola cannot be transmitted through the air as is the case with the flu and other contagious conditions in which respiratory secretions are coughed or sneezed. People who've contracted it in West Africa have had direct skin-to-skin contact with a person exhibiting frank Ebola symptoms, experts say. "Ebola is a scary disease because of the severity of illness it causes," Frieden said.Still, there are unknowns. For example, authorities have yet to determine how or where in Liberia the man was infected.

The patient, according to Frieden, "was visiting family members who live in this country," when his symptoms emerged."We will contact anyone who has had any contact with the individual while infectious," Frieden said. "At the moment that doesn't include anyone who hadtraveled with him."

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