The number of confirmed cases in the Ebola outbreak in the eastern Democratic Republic of the Congo (DRC) has surpassed 1,000, health officials say, as violence and mass displacement undermine efforts to contain the virus.

DRC’s Ministry of Health said on Sunday that 1,003 people had been infected and 254 had died since the outbreak, centred in the northeastern Ituri province, was declared on May 15. A total of 100 people have recovered, while at least 365 are in hospital or isolation.

The outbreak is caused by the rare Bundibugyo strain of Ebola, for which there is no approved vaccine or specific treatment, and it was the country’s worst on record in its first month. Officials acknowledge that many infections are likely going undetected and that the peak of the epidemic may still lie ahead.

Contact tracing has reached only about 55 percent of those who may have been exposed, the ministry said, leaving major gaps in the response.

“If you want to control an outbreak, especially an Ebola outbreak, you must know the index case. We don’t have confidence in when this outbreak started,” Dr Jean Kaseya, director general of the Africa Centres for Disease Control and Prevention, told The Associated Press news agency last week.

Violence is hampering access to affected communities. Attacks by the ISIL-linked Allied Democratic Forces in Ituri have cut off villages and forced thousands to flee into overcrowded camps.

At the Kigonze displacement camp near Bunia, where more than 20,000 people have sought shelter, officials reported 10 unexplained deaths last week and called for an urgent investigation, though no Ebola cases have been confirmed.

“If a disease or epidemic were to spread among the thousands of people living at this site, it would be a real catastrophe, given our already very precarious living conditions,” said Charite Banza, a civil society leader in Ituri.