A patient being treated at a Dallas hospital tested positive for Ebola, the first case of the disease to be diagnosed in the United States, federal health officials announced Tuesday.

Officials at Texas Health Presbyterian Hospital said the unidentified patient is being kept in isolation and that the hospital is following Centers for Disease Control and Prevention recommendations to keep doctors, staff and patients safe.

The hospital had announced a day earlier that the patient's symptoms and recent travel indicated a case of Ebola, the virus that has killed more than 3,000 people across West Africa and infected a handful of Americans who have traveled to that region.

The CDC has said 12 other people in the U.S. have been tested for Ebola since July 27. Those tests came back negative.

The National Institutes of Health recently admitted an American doctor exposed to the virus while volunteering in Sierra Leone. Four other patients have been treated at hospitals in Georgia and Nebraska.

According to the CDC, Ebola symptoms can include fever, muscle pain, vomiting and bleeding, and can appear as long as 21 days after exposure to the virus.