Former U.S ebola Doctor previously discharged has been re-admitted

(CNN) -- An American patient treated for Ebola in Nebraska then released is now in isolation in a hospital in Massachusetts. And an Ebola patient in Dallas has slipped into critical condition.

Dr. Richard Sacra had worked as a medical missionary in Liberia but not directly with Ebola patients. Nevertheless, he contracted the disease. He was treated in isolation at the Nebraska Medical Center in Omaha then released after testing negative for the virus.

Early Saturday, he went to an emergency room in Boston with a cough and fever, said missionary organization Serving in Mission. He was afraid he might have pneumonia.Because of his previous infection, he was transferred to the UMass Memorial Medical Center in Worcester, the center said in a statement.Doctors there don't believe it is a recurrence of Ebola, but are keeping Sacra in isolation, in accordance with guidelines from the Centers for Disease Control and Prevention, until they are sure what is causing his symptoms.

"We're waiting for final test results from the CDC, which we expect to receive late Monday," said lead physician Dr. Robert Finberg.