Thomas Eric Duncan was not diagnosed with Ebola until September 30 and he died on October 8.
"Unfortunately, in our initial treatment of Mr Duncan, despite our best intentions and a highly skilled medical team, we made mistakes," admitted Dr Daniel Varga, chief clinical officer of Texas Health Resources, which runs the hospital.
"We did not correctly diagnose his symptoms as those of Ebola. We are deeply sorry," he said, in written testimony to politicians on the House Energy and Commerce Committee, which is studying the public health response to the outbreak.
The CDC has identified 118 people who either had definite or possible contact with Duncan, more than half of whom are healthcare workers.
The first case of infection in the US was announced on Monday, in Nina Pham, a nurse who had cared for Duncan, followed by another female healthcare worker on Wednesday. She has been identified as nurse Amber Vinson.
The Centres for Disease Control and Prevention (CDC) chief Thomas Frieden described the situation as "very concerning".
"The investigation is identifying additional healthcare workers who will be very closely monitored and we are planning for the possibility of additional cases in the coming days," he said.
The CDC issued an alert for all 132 passengers who travelled on an October 13 flight from Cleveland, Ohio to Texas with the Ebola-infected nurse who had not yet become symptomatic.
Frieden warned that health workers who have been exposed to Ebola patients should not use public transport.
The woman was isolated at Texas Health Presbyterian hospital in Dallas on Wednesday with a fever, and the crew on the flight said she had not been symptomatic when she flew a day earlier.
National Nurses United said that their discussions with staff at the Texas Health Presbyterian Hospital Dallas revealed the facility was woefully unprepared to deal with an Ebola patient when Duncan arrived.
AFP