WASHINGTON (AFP) -- A Texas health care worker who treated a man who later died of Ebola has tested positive for the disease in a preliminary test, doctors said Sunday, the second person to be diagnosed with the illness on US soil.

"We knew a second case could be a reality, and we've been preparing for this possibility," said Dr David Lakey, commissioner of the Texas Department of State Health Services.

"We are broadening our team in Dallas and working with extreme diligence to prevent further spread."

The health care worker reported a low grade fever Friday night and was isolated and referred for testing, Texas health services said in a statement. It did not further identify the worker nor detail how exposure to the virus occurred.

The statement added: "Health officials have interviewed the patient and are identifying any contacts or potential exposures. People who had contact with the health care worker after symptoms emerged will be monitored based on the nature of their interactions and the potential they were exposed to the virus."

The health care worker was from Texas Health Presbyterian Hospital in Dallas, the hospital which treated Thomas Eric Duncan, the Liberian man who died on Wednesday.