Five U.S. healthcare workers who underwent monitoring at a Nebraska medical center after possible exposure to the Ebola virus in West Africa have completed their quarantine periods and were symptom-free, the hospital said on Tuesday.

The workers underwent monitoring for 21 days at the Nebraska Medical Center in Omaha after participating in a mission to Sierra Leone where a colleague tested positive for Ebola.

Four of the individuals have since left the area and the fifth, who had an unrelated cardiac issue while jogging near the facility over the weekend, has been discharged and would soon leave the city, the hospital said on its Twitter account.

More than 10,300 people have died in West Africa over the last year from the worst detected outbreak of Ebola, which has plagued Guinea, Liberia and Sierra Leone, World Health Organization figures show.