The Ebola outbreak tearing through northeastern Congo is spreading far more widely than official figures show, a senior World Health Organization official warned on Thursday, as four out of every five new Ebola cases surface with no traceable link to a known patient.
Chikwe Ihekweazu, the WHO’s emergencies director, told reporters that roughly 80% of new confirmed Ebola patients in Bunia, the epicenter of the crisis in Ituri province, are turning up outside established contact-tracing lists. That gap, he said, points to a chain of Ebola transmission that health workers are struggling to see, let alone contain.
The outbreak, declared in mid-May, has officially infected 1,792 people and killed 625, according to government data released Thursday. However, WHO modeling based on test positivity rates suggests the true Ebola toll could be two to four times higher than those numbers indicate, Ihekweazu said. This is a gap that underscores how much of the epidemic is unfolding beneath the surface.
“Eighty percent of the new patients confirmed are coming outside of known contact lists,” Ihekweazu said of the situation in Bunia, a city of roughly one million people where about one in every two people tested for Ebola comes back positive — a sign, he said, of intense and ongoing transmission within the community.
The picture is not uniform across the country. In North Kivu province, where case counts are lower, Ihekweazu said almost all new infections are still being identified through known contacts, a sign that surveillance efforts there are functioning better than in Ituri. About 90% of all reported cases remain concentrated in Ituri, particularly in the health zones of Bunia, Rwampara, Mongbwalu and Nyakunde, though the virus has also pushed into North Kivu, South Kivu and, more recently, Tshopo province.
Part of what is complicating the response, Ihekweazu said, is the specific strain driving this outbreak. Preliminary evidence suggests the Bundibugyo strain of Ebola may cause milder symptoms than other forms of the virus, which appears to be lulling some communities into underestimating the danger. Families in affected areas have in some cases opted to care for sick relatives at home rather than seek treatment immediately, he said.
That pattern cuts both ways. While patients who eventually reach treatment centers appear to be surviving at higher rates, the delay also means infectious individuals often remain within their communities far longer than health officials would like, extending the window in which the disease can spread.
“Patients are out there much longer than we would like,” Ihekweazu said. “The longer patients are outside of care, the more likely they are to transmit this illness.”
Deaths outside formal medical settings remain a significant concern for Ebola responders. An analysis of the first 400 fatalities in the outbreak found that roughly 70% occurred outside treatment centers, according to Ihekweazu, complicating efforts to track how and where the virus is moving.
Improving surveillance is now the central challenge facing the Ebola response, he said. Authorities this week launched an effort to train 21,000 community health workers who will conduct house-to-house visits, identify suspected cases and encourage symptomatic residents to seek medical care rather than remain at home.
The World Health Organization has previously flagged the Congo Ebola outbreak as a growing international concern, and the U.S. Centers for Disease Control and Prevention raised its own response posture to the highest level last month, though it said the risk of the virus spreading within the United States remained low.
For now, officials in Ituri say halting the Ebola outbreak will depend on closing the gap between the cases they can see and the ones still moving undetected through affected communities.
