OMAHA, Neb. (AP) — Four American aid workers who were exposed to Ebola while working in Sierra Leone are being monitored at a Nebraska hospital.

Nebraska Medical Center spokesman Taylor Wilson says the four individuals arrived in Omaha around 5:30 p.m. Saturday.

Those four are part of a group of 10 clinicians who were evacuated after one of their colleagues contracted the deadly virus. They were all working with the Boston-based nonprofit Partners in Health.

Wilson said Sunday morning that none of the four people being monitored in Omaha were sick. If any of them do develop Ebola, they will be treated in the hospital’s specialized biocontainment unit.

The other clinicians exposed to Ebola will be monitored at U.S. hospitals with experience treating the disease in Atlanta and in Bethesda, Maryland.