FREETOWN, Sierra Leone: Ten clinicians with a Boston-based nonprofit organization responding to Sierra Leone’s Ebola outbreak are to be evacuated to the United States after one of their colleagues was infected with the deadly disease.

Partners in Health said in a statement Saturday that the medical workers, who will together form the largest group to be evacuated to the United States over possible Ebola exposure, would travel on non-commercial aircraft and be isolated in Ebola treatment facilities.

On March 11, a Partners in Health clinician in Sierra Leone tested positive for Ebola, and the 10 fellow workers “came to the aid of their ailing colleague,” the group’s statement said. The 10 have not shown signs of Ebola and Partners in Health said the evacuations were ordered “out of an abundance of caution.”

“They will remain in isolation near designated US Ebola treatment facilities to ensure access to rapid testing and treatment,” the group’s statement said.

The clinician who became infected has already been evacuated and is receiving treatment at the National Institutes of Health in Bethesda, Maryland.

Partners in Health did not specify a timeline for the new evacuations and a representative of the US Embassy in Freetown, Sierra Leone’s capital, was not authorized to comment Sunday morning.

On Saturday, the Centers for Disease Control and Prevention said several Americans who may have been exposed to Ebola in Sierra Leone would be monitored. The CDC did not state how many Americans are coming back, but University of Nebraska Medical Center officials said they will be monitoring four Americans.

“Because we have individuals to monitor simultaneously, the safest and most efficient way to do that is in a group setting,” Phil Smith, director of the center’s Biocontainment Unit, said on Saturday. Smith’s unit would evaluate and treat any patients who develop symptoms. He said that patients would be quarantined and kept away from other patients, students and staff.

Partners in Health began treating Ebola patients in Liberia and Sierra Leone last November, and the clinician who tested positive for Ebola on March 11 is the first staff member to fall ill “as a result of a confirmed occupational exposure,” the group said. It has more than 2,000 employees working in West Africa, including foreigners and locasl and 600 Ebola survivors.

The World Health Organization estimated last week that the ongoing Ebola outbreak has killed more than 10,000 people, mostly in the West African nations of Guinea, Liberia and Sierra Leone. The outbreak is the largest ever for the disease. The rate of deaths has slowed dramatically in recent months but the virus appears stubbornly entrenched in parts of Guinea and Sierra Leone.