Health officials said Wednesday that Dr. Richard Sacra -- who contracted Ebola while volunteering in West Africa -- is expected to make a full recovery.

Doctors at the Nebraska Medical Center in Omaha, where Sacra is being treated, based their optimistic assessment on blood tests that show the amount of virus in his system declined from the first to the fifth day of treatment. Sacra's doctors are still awaiting results from a second set of blood samples to confirm their prognosis.

Doctors said Sacra received an experimental drug, which they have not identified, for seven days but is no longer taking it.

"He looks great in person," Dr. Phil Smith, medical director of the Biocontainment Unit at the Nebraska Medical Center, said in a press statement. "We're hopeful the latest round of lab data reflects what we're seeing in his room."

Get Breaking News Delivered to Your Inbox

However, hospital officials said they aren't yet ready to release Sacra until they've confirmed the infection has cleared and that he hasn't suffered any serious complications.

Sacra, 51, arrived in the U.S. from Liberia on Sept. 5, sick but in stable condition. He was the first Ebola patient treated at the Nebraska Medical Center, the largest of four special isolation units in the U.S.

"We are still somewhat cautious because of the severity and unknown factors of this disease," Dr. Angela Hewlett, associate medical director of the Biocontainment Unit at The Nebraska Medical Center, said in a press statement. "We know from experience how other patients look as their condition improves, but since we have so little experience treating patients with Ebola, that tempers our optimism a little bit."

Two other American Ebola patients, Dr. Kent Brantly and Nancy Writebol, were treated at Emory University Hospital in Atlanta and released last month.