"We understand that his situation has taken a turn for the worse," Frieden said at a news conference in Atlanta Sunday afternoon.

Updated — Oct. 5, 11:10 p.m. ET: The Ebola patient in a hospital is "fighting for his life," the director of the Centers for Disease Control and Prevention Dr. Thomas R. Frieden said Sunday

The Texas Health Presbyterian Hospital in Dallas where Duncan is being treated previously said that the Ebola patient was being kept in isolation, and that "his condition was serious but stable."

Dallas county prosecutor says they're looking into whether #ebola patient knowingly and intentionally exposed the public to a deadly virus

Dallas county prosecutor says they're looking into whether #ebola patient knowingly and intentionally exposed the public to a deadly virus

The Texas Department of State Health Services said on Friday they are monitoring 50 people who came into contact with Ebola patient Thomas Eric Duncan and that 10 of those peope are at high risk.

Dallas County officials said Thursday that 100 people came in direct or indirect contact with Duncan, 42, before he was isolated. These include 12 to 18 people who had direct contact with the patient, including his family and EMS crews.

Dr. David Lakey, Commissioner of Texas Department of State Health Services, said on Friday they have narrowed their scope down to 50 people who came in contact with the first U.S. Ebola patient and are monitoring them daily for symptoms. Of these, 10 individuals are at high risk. The rest are "low-concern" contacts, Lakey said in a press briefing.

A member of the public health team visits these 50 people daily, and their temperature is checked twice a day. Lakey said all these individuals are doing well and don't have any symptoms consistent with Ebola at this time.

Texas health officials on Wednesday ordered four of Duncan's family members who had contact with him to stay home and forbid visitors to prevent the spread of the disease, NBC News reported. The order requires them not to leave their homes until at least Oct. 19 when the incubation period passes.