There have been 69 cases in all including nine confirmed by a lab, the World Health Organization said, and five of the deaths have been confirmed by lab work.
The Ebola virus has no cure and is deadly in 40 per cent to 90 per cent of cases. The disease causes severe internal bleeding.
"The situation is serious," Fadela Chaib, a spokeswoman for the Geneva-based agency, told reporters.
She said it was unusual that the first person to be infected was a health worker. Normally someone working outside would have been the first, as has mostly been the case in the eight previous Ebola epidemics in Congo since the first discovery of it in 1976. This is the first outbreak in the Haut-Uele territory, in northeastern Congo.
Authorities had said last week that 15 people had died in northeastern Congo, where the tradition of washing and displaying of corpses before funerals spreads the epidemic. The tradition is intended to show love and respect for the deceased, but the practice also brings people into close contact with victims of the deadly virus.
Aid group Doctors Without Borders, along with WHO and Congo's health ministry, have been conducting education campaigns in the area to warn people of the risks linked to this practice.
Doctors without Borders also is managing two quarantine centres in Isiro and Viadana and the U.N. has called for the creation of a $2 million fund to fight the epidemic.