At least two American charity workers infected with the Ebola virus in western Africa will be transferred to the United States for treatment, CNN reports.

Dr. Kent Brantly and Nancy Writebol are both in “stable but grave condition,” according to a statement from Samaritan’s Purse, the charitable organization for whom they work in Liberia.

The group is also evacuating all but “the most essential personnel” from areas affected by the outbreak.

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One of the patients will be treated at Atlanta’s Emory University Hospital, one of four medical facilities in the United States with a special isolation unit used to safely contain and treat Ebola.

So far the outbreak has killed 729 people, according to the World Health Organization.