Authorities have confirmed an Ebola case just 70 kilometers (43 miles) from Congo's border with South Sudan.
The development is troubling as South Sudan's health care system is less equipped to handle Ebola should cases develop there.
The report of the case near South Sudan came Tuesday from South Sudan's health ministry and was seen by The Associated Press.
Health officials say the confirmed case near South Sudan involved the contact of a known Ebola case in Congo's Beni town.
The person was supposed to stay in regular contact with Congolese health authorities during the 21-day incubation period.
Congo's Ebola outbreak has killed more than 1,500 and has spread to neighboring Uganda where two people died last month after a family that sickened in Congo returned home across the border.