A United Nations employee in eastern Democratic Republic of the Congo has tested positive for Ebola, the first such incident during the current outbreak, according to the head of the UN peacekeeping mission.

“I am writing today to inform you that my leadership team and I have regretfully just received news that a UN colleague based in Beni has tested positive for Ebola and is now receiving the necessary medical treatment,” Leila Zerrougui wrote in the letter seen by Reuters.

Zerrougui said the employee had not been to work for several weeks and that tracing the person’s contacts had begun.

The news came after health officials warned that the rate of new Ebola cases had more than doubled since September after rebel violence in north-eastern DRC caused response efforts to be briefly suspended, health officials said on Thursday.

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The International Rescue Committee (IRC) said it was alarmed that there were 33 new cases between 1 and 9 October, compared with 41 cases during all of September.

Most of the new cases have been in Beni, where experts had to suspend Ebola containment efforts for days after a deadly rebel attack. With multiple armed groups active in the region, health officials have said they are effectively operating in a war zone.

“This is a sign not only that the outbreak is not under control, but that without full engagement from the community things could get a lot worse,” said Dr Michelle Gayer, the IRC’s senior director of emergency health.

Earlier this week, the World Health Organization said that 19 of the health workers who had caught Ebola in this epidemic had been infected outside of hospitals or clinics, meaning the virus is spreading in the community.

WHO warned that the risk of Ebola’s regional spread was very high, pointing out that DRC’s affected North Kivu and Ituri provinces share borders with Uganda and Rwanda. WHO said the risk for international spread remained low.

Ebola is a haemorrhagic fever that spreads through contact with the bodily fluids of its victims and typically kills about half of those it infects.