The first patient to be diagnosed with a confirmed case of Ebola in the United States was reported by health officials on Tuesday.

The patient had flown into Texas from Liberia on September 20. Six days after arrival, the unidentified man went to Texas Health Presbyterian Hospital where he was admitted. He has been in isolation since Sunday and is reported to be in critical condition.

Ebola symptoms can present themselves anytime between two to 21 days after infection occurs. A person is not contagious until the symptoms begin. The patient traveled without symptoms and did not develop them until four to five days after his arrival in the states.

Dr. Thomas Friedlander, director of the CDC, stated that those traveling with the man were not at risk of developing an infection because of his lack of symptoms while on the flight. Family and friends that the man came in contact with once he had arrived are being contacted for screening, however.

While this case is a stark reminder of how the Ebola outbreak ravaging West Africa could spread on a global scale, Friedlander reminds the American public that the possibility for an outbreak in the U.S. is unlikely. Already several patients with Ebola infections have been treated in the states, and the stringent use of isolation and other safety precautions by medical professionals has ensured the disease stay contained to those few people already infected.

Because of the often delayed onset of symptoms, the eventual certainty that someone would travel to the country unaware of their infection was something that hospitals around the country have been preparing for, Frieden said.

In a statement, Frieden said, “The bottom line here is that I have no doubt we will control this importation, or this case of Ebola, so that it does not spread widely in this country.”

So far, the outbreak in West Africa has claimed more than 3,000 lives.