GENEVA — 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 time frames in an outbreak as complicated as this with so many variables that are outside our control," WHO emergency response chief Peter Salama told reporters, "but certainly we’re planning on at least another six months before we can declare this outbreak over.”

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 presents perhaps the most difficult circumstances the WHO has ever encountered, due to a dense and mobile local population, insecurity caused by two armed groups, and its spread by transmission in health centers, Salama said.

One of the major drivers of the spread of the disease has been people visiting the several hundred health centers in the town of Beni, he said.

Health workers help an Ebola patient into her bed inside a Doctors Without Borders treatment center on Nov. 3. John Wessels / AFP — Getty Images file

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

The facilities are unregulated and informal, and vary from standalone structures to rooms in private house. They are not set up to spot Ebola, let alone tackle cases of the disease.

Many had no running water for hand washing, and patients — who generally opted for injectable medicine because they believed it was a stronger form — 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 health centers.