FREETOWN, Sierra Leone — Ten health care workers 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 10, the largest group to be evacuated to the United States over possible Ebola exposure, would travel on noncommercial aircraft and be isolated in Ebola treatment facilities.

Four of the 10 health care workers arrived at Nebraska Medical Center in Omaha around 5:30 p.m. Saturday, spokesman Taylor Wilson said Sunday. None of them was sick, but if they do develop Ebola they will be treated in the hospital’s specialized biocontainment unit.

The others will be monitored at U.S. hospitals with experience treating the disease, in Atlanta and in Bethesda, Maryland.

On March 11, a Partners in Health medical worker in Sierra Leone tested positive for Ebola, and the 10 fellow workers “came to the aid of their ailing colleague,” the organization’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 U.S. Ebola treatment facilities to ensure access to rapid testing and treatment in the unlikely instance that any become symptomatic,” the group’s statement said.

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

Partners in Health did not specify a time for the remaining evacuations and a representative of the U.S. Embassy in Freetown, Sierra Leone’s capital, referred questions to Partners in Health and the U.S. Department of Health and Human Services.

The World Health Organization says the outbreak has killed more than 10,000 people.