A total of 100 people have recovered in the outbreak concentrated in the Ituri province since it was declared on May 15, Congo's Ministry of Health said.

The Ebola outbreak caused by the rare Bundibugyo virus, which has no vaccines or treatment, was the worst ever in its first month. Officials admit there could be far more cases they still don't know about and that the peak of the outbreak is still ahead.

Contact tracing remains a key issue for local authorities, who have only achieved a 55 per cent coverage rate, the ministry said.

Officials also are yet to identify the outbreak's patient zero and still need to trace more than 35,000 people who have come in contact with infected individuals as of last week, authorities said.