Another person infected with Ebola virus is headed to the U.S. for treatment, Emory University Hospital confirmed Monday. This is the fourth person infected in West Africa to seek treatment in the United States, and the third to be treated at Emory’s special biocontainment unit. The staff there are experienced, after successfully treating the first two U.S. patients — medical missionaries Nancy Writebol and Dr. Kent Brantly.

“The patient is being transported by air ambulance from West Africa. The patient is expected to arrive tomorrow morning. We do not know exactly what time the patient will arrive,” Emory said in a statement. “We are bound by patient confidentiality and have no information regarding the status of the incoming patient.” The World Health Organization declined to say if the patient is a WHO doctor infected in Sierre Leone. A third patient, medical missionary Dr. Rick Sacra, is being treated at a different but similar biocontainment unit at the University of Nebraska Medical Center. Infectious disease experts say there is very little chance the virus will spread in such units, where extreme precautions are taken.

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— Maggie Fox