Three Liberia-based missionaries, including the husband of a missionary being treated for Ebola in Atlanta, have returned to the United States and will be quarantined to ensure they did not contract the deadly virus, their Christian group said on Monday.

SIM USA worker David Writebol and two doctors who have been treating Ebola patients in Monrovia amid the current outbreak arrived in Charlotte, North Carolina, by private charter Sunday night, the mission organization said in a statement.

Writebol's wife, Nancy, is one of two American relief workers with Ebola getting treated at Emory University Hospital.

SIM USA said none of the other missionaries it brought back had shown signs of being infected with the disease, which has killed nearly 1,000 people in West Africa and is the worst outbreak on record.

Health officials in Charlotte said they would require, as a preventative measure, the three to remain under a 21-day quarantine that began in Liberia. Three weeks is the longest incubation period between someone getting exposed to Ebola and the onset of the infection.

The missionaries will spend that time in a private area on SIM USA's campus in Charlotte, the organization said, adding that Writebol will visit his wife once the quarantine ends.

"We are excited to have these three missionaries safely back in the U.S.," SIM USA President Bruce Johnson said in a statement. "They are all healthy and in good spirits."