The Ebola outbreak in the Democratic Republic of Congo may be significantly larger than official figures indicate, with most new infections occurring outside known chains of transmission, raising concerns that health authorities are struggling to keep pace with the spread of the virus.
According to the World Health Organization (WHO), around 80% of newly confirmed Ebola patients in the outbreak’s epicentre are not identified through existing contact-tracing networks, suggesting widespread undetected community transmission.
The outbreak, declared in mid-May, has officially infected 1,792 people and killed 625, according to Congolese government figures released on Thursday. However, WHO modelling indicates the true number of infections could be two to four times higher.
Most new infections are outside known contact networks
WHO Emergencies Director Chikwe Ihekweazu told Reuters that in Bunia, the centre of the outbreak in Ituri province, four out of every five newly confirmed cases are emerging outside the lists of people already being monitored after exposure to infected patients.
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Public health experts view contact tracing as one of the most effective tools for controlling Ebola. When large numbers of patients are not linked to known cases, it suggests the virus is circulating undetected in the community, making containment much more difficult.
In contrast, neighbouring North Kivu province has shown encouraging progress, with nearly all new infections occurring among previously identified contacts.
Transmission remains concentrated in eastern Congo
Around 90% of all confirmed cases remain concentrated in Ituri province, particularly in the health zones of Bunia, Rwampara, Mongbwalu and Nyakunde, where transmission remains intense.
The outbreak has nevertheless expanded beyond its original epicentre, reaching North Kivu, South Kivu and more recently Tshopo province.
In Bunia—a city of roughly one million people about half of all individuals tested for Ebola receive positive results, reflecting sustained community transmission.
Milder symptoms may be helping the virus spread
Health officials believe the Bundibugyo strain responsible for the outbreak may produce milder symptoms than other Ebola variants.
While this appears to improve survival prospects for patients who eventually reach treatment centres, it may also encourage infected individuals to remain at home longer or seek medical attention later, unknowingly spreading the virus to family members and the wider community.
According to WHO, prolonged delays before isolation increase opportunities for transmission.
Community deaths remain another major concern. An analysis of the first 400 Ebola fatalities found that roughly 70% occurred outside designated treatment centres, highlighting continued challenges in identifying patients early enough to provide care and prevent further spread.
Health authorities expand surveillance
To improve detection, Congolese authorities have begun training approximately 21,000 community health workers to conduct door-to-door visits, identify suspected infections and encourage symptomatic individuals to seek medical treatment.
Officials hope stronger community surveillance will help uncover hidden chains of transmission and improve contact tracing, which remains the cornerstone of Ebola control efforts.
Hidden transmission is the outbreak’s biggest threat
The most alarming aspect of Congo’s latest Ebola outbreak is not simply the number of confirmed cases but the large proportion of infections occurring outside established surveillance networks. When 80% of new patients are unknown to contact tracers, it indicates the virus is spreading faster than health authorities can detect it.
Although the Bundibugyo strain may cause comparatively milder illness, that characteristic presents a paradox: fewer severely ill patients can reduce public perception of risk, delaying diagnosis and allowing infected individuals to remain in the community longer. Combined with high rates of deaths occurring outside treatment facilities, these trends point to persistent gaps in surveillance rather than failures of medical treatment.
The rapid expansion of community health worker programmes reflects recognition that traditional outbreak response measures alone may not be sufficient. Unless surveillance improves and hidden transmission chains are identified quickly, the outbreak is likely to remain substantially larger than official figures suggest, complicating efforts to bring it under control.
With information from Reuters.
