KINSHASA, Congo (AP) — A U.S. citizen working for a humanitarian organization in Congo has tested positive for the Ebola virus, the U.S. Centers for Disease Control and Prevention said on Friday, as the Central African country struggles to contain the swelling outbreak.

The CDC said it was working with the person’s employer, U.S. agencies, the public health authorities and Congolese partners to prevent further transmission and identify close contacts. It did not provide any further details.