Dr. Chikwe Ihekweazu, director of emergency operations at the World Health Organization, warned that the actual extent of the Ebola outbreak in the Democratic Republic of Congo may be two to four times larger than official data, stressing that four out of every five new infections are not linked to known cases.

Ihekweazu said in an interview with Reuters: "80% of newly confirmed patients are not on the lists of known contacts" in the epicenter of the outbreak in the city of Bunia, capital of Ituri province.

Government data showed that the outbreak, declared in mid-May, has infected some 1,792 people and killed 625 others, while WHO estimates are based on mathematical models and test positivity rates to reach these alarming figures.

About 90% of all reported cases are concentrated in Ituri province, but the virus has spread beyond the main hotspot to North Kivu and South Kivu provinces, and more recently to Tshopo province.

Ihekweazu noted that about half of the patients tested in Bunia, which has a population of about one million, tested positive, indicating widespread and ongoing transmission within the local community.

In contrast, the official expressed some optimism about areas with fewer cases, such as North Kivu province, where almost all new cases come from lists of known contacts, which he described as an indication of some progress in containment efforts.