The World Health Organization says insecurity and lack of access in conflict-ridden parts of the Democratic Republic of Congo remain major threats to ending the Ebola outbreak there.
The latest reports put the number of confirmed cases at 3,354, including 2,218 deaths.
Health officials are concerned progress made against the Ebola outbreak in the North Kivu and Ituri provinces could come undone because of ongoing fighting among dozens of armed groups.
The World Health Organization says the deadly virus has been cleared from 25 of the region's health zones. It says an average of four to 10 new cases a week have been recorded in four zones in recent weeks.
However, the executive director of the WHO's Health Emergencies Program, Michael Ryan, says there's been a big increase recently in the number of cases in North Kivu's Mabalako zone.
"Last week, four to 10 of December, the number of cases jumped to 27 in a single week,” Ryan said. “That is nearly a three-fold increase, more than a three-fold increase in one week, which is quite remarkable."
Ryan told VOA the new cases are linked to a single chain of transmission stemming from one infected individual.
"This case was a case, most likely of a lapsed infection or someone who relapsed from having been previously recovered,” Ryan said. “And, this has occurred in an area that is quite insecure and been very difficult to operate in … and it is most worrying because one of the contacts from that transmission chain ended up moving to (the city of) Butembo and died in Butembo."
Ryan recalls that six months ago, Ebola was raging in Butembo, which is also in North Kivu. He says there is real concern that continued transmission of the virus in Mabalako could potentially re-infect Butembo, which would be a major setback to Ebola containment efforts.