The Ebola outbreak erupting from the Ituri province of the Democratic Republic of the Congo continues to escalate wildly, with cases nearing 750, deaths reported at 177, and around 1,400 contacts now being traced, the World Health Organization reported in a press briefing Friday. The latest numbers already place the outbreak as the third largest on record, though it was only first reported a week ago, on May 15. And WHO Director-General Tedros Adhanom Ghebreyesus said the outbreak is still “spreading rapidly.”

A revised WHO assessment has moved the risk level from “high” to “very high” at the national level, while risk remains “high” at the regional level and “low” at the global level, Tedros added.

WHO officials have acknowledged that a delay in detecting and responding to the outbreak enabled it to balloon, and that they are now racing to get ahead of the virus.

WHO representative Dr. Anne Ancia spoke during today’s briefing from the DRC, saying that when officials got to the area, they found the virus was “already rampant and silently disseminating for a few weeks already.” In the outbreak investigation so far, the earliest known suspected case was in a health worker, who developed symptoms on April 24 in Bunia, the capital city of Ituri. WHO only got word of a potential outbreak on May 5, with news of a cluster of deadly, unidentified infections that led to the deaths of four health workers. By the time a WHO team arrived, there were already 80 cases.

“Now we are sprinting behind [the virus] so that we can really try to control this outbreak, and because it is still transmitting for the time being, yes, the number [of cases] will keep rising for some time until we are really able to put all the response operation in place,” she said.

Their work is made harder by various challenges. The virus behind the Ebola outbreak is the uncommon Bundibugyo virus, which doesn’t have established vaccines or therapeutics. That leaves active case finding, isolation, and contact tracing as the primary tools to halt the spread. Moreover, the virus is spreading in areas with armed conflict, intense population mobility, weak health systems, and where millions face acute hunger and need humanitarian assistance.