An Ebola patient is being checked by two medical workers after being admitted into a Biosecure Emergency care Unite (CUBE) on August 15, 2018 in Beni, Democratic Republic of the Congo.

The Ebola outbreak in northeastern Democratic Republic of Congo, which has already killed more than 200 people, is expected to last until mid-2019, a senior World Health Organization official said on Tuesday.

"It's very hard to predict timeframes in an outbreak as complicated as this with so many variables that are outside our control, but certainly we're planning on at least another six months before we can declare this outbreak over," WHO emergency response chief Peter Salama told reporters.

The outbreak in Congo's North Kivu province has caused 333 confirmed and probable cases of the deadly virus, and is now the worst in Congo's history.

The location of the disease is perhaps the most difficult the WHO has ever enountered, due to a dense and mobile local population, insecurity caused by two armed groups, and its spread by transmission in health centres, Salama said.

One of the major drivers of the spread of the disease was due to people visiting the several hundred "tradi-modern" health centres in the town of Beni, he said.

"Those facilities, we believe, are one of the major drivers of transmission," he said.

The tradi-modern facilities were unregulated, informal, and varied from being a standalone structure to a room in someone's house, and were not set up to spot Ebola, let alone tackle cases of the disease.

Many had no running water for handwashing, and patients - who generally opted for injectable medicine because they felt it gave them a stronger form of medicine - would reuse needles.

"With the injections come the risks," Salama said.

There had been an epidemiological breakthrough around late October, when a change in the age distribution of Ebola patients revealed that many of them were children being treated for malaria in the tradi-modern health centres.