The first person to be diagnosed with Ebola on U.S. soil is listed in critical condition, revealed the Texas Health Presbyterian Hospital Dallas, the hospital where the patient is currently being treated, on Saturday.

Thomas Eric Duncan was diagnosed with Ebola following a trip to the U.S. from Liberia, where he helped a pregnant woman who eventually died of the infectious disease. His diagnosis was confirmed by the U.S. Centers for Disease Control and Prevention on Sept. 30.

Duncan had already arrived in Dallas from Liberia on Sept. 20 before he started showing symptoms of the hemorrhagic fever, which has so far caused the death of about 3,400 people in West Africa in an unprecedented Ebola epidemic. He started to show symptoms on Sept. 24 but was mistakenly released from the hospital when he first sought treatment.  His was diagnosed after he was readmitted on Sept. 28.

Health officials said that they are monitoring about 50 individuals who may have come in contact with Duncan. Of these, nine are believed to have increased risk of contracting the virus, albeit none has so far exhibited symptoms of the disease. Included in this group are the patient's family members and some health care workers.

 CDC director Tom Frieden said that of particular concern are those who rode with Duncan in the ambulance that took him to the hospital. These individuals are currently being observed for signs of infection.

"Because we can't be certain they didn't have contact, we will be monitoring them as well," Frieden said.

Five public school children were also possibly exposed, but Dallas Independent School District superintendent Mike Miles said that as a precautionary measure, these children had been kept from attending their classes in the past days as they are being monitored.

Public health officials acknowledged the possibility that some of the people who had been in close contact with the patient will develop Ebola, which has an incubation period of up to 21 days. Officials are nonetheless confident that further spread of the fatal disease won't likely happen in the Dallas area because of the monitoring.

Duncan was staying at an apartment in Dallas when he started to exhibit symptoms. Health officials said that the people who lived in the apartment including Duncan's partner, identified as Louise Troh, her 13-year old son, and two adult nephews had moved to an isolated house in an identified gated community within the city.

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