Contact tracing has always been one of the most demanding and resource-intensive tools in outbreak response. It requires identifying every person a sick individual has encountered, locating those people, monitoring them for signs of illness, and repeating the process across an entire epidemic curve. Now, an ongoing Ebola outbreak in the Democratic Republic of Congo is revealing just how much harder that already-daunting task becomes when the disease looks like almost everything else.
The current outbreak, first detected in mid-May 2026, has officially sickened more than 1,000 people and killed more than 250, according to the DRC’s health ministry. The World Health Organization and international partners are leading the response, concentrated in Ituri Province in eastern DRC. But the true scale of transmission is likely significantly larger — and a growing body of evidence suggests the outbreak may have been spreading undetected for months before it was recognized.
A Different Virus Strain, A Different Clinical Picture
The strain driving this outbreak is Bundibugyo, a species of Ebola virus distinct from the Zaire strain responsible for the devastating 2014 West Africa epidemic, which killed more than 11,000 people. Bundibugyo carries a lower fatality rate: roughly under 30 percent in the current outbreak, compared to case fatality rates that can exceed 80 percent with Zaire Ebola in the absence of vaccines and treatment.
Early assessments by the DRC’s Ministry of Health, reported by the WHO’s outbreak response lead Dr. Marie-Roseline Belizaire, suggest that approximately 90 percent of current patients are not developing the severe hemorrhagic symptoms — the extensive internal and external bleeding — that have historically made Ebola outbreaks so visually and clinically unmistakable. In previous Zaire outbreaks, roughly half of patients reached that stage.
What patients do experience in the earlier phases of illness — fever, body aches, fatigue, diarrhea, and vomiting — overlaps almost entirely with malaria, typhoid, dysentery, and a range of other endemic diseases common in the DRC. Without the dramatic clinical presentation that historically prompted urgent care-seeking and immediate alarm in communities, patients may remain ambulatory and socially active far longer than in previous outbreaks, unknowingly exposing others throughout the course of their illness.
Contact Tracing Numbers That Don’t Add Up
The implications for contact tracing are severe. Under normal outbreak conditions, a confirmed Ebola case might be expected to name between 15 and 40 contacts during an interview. In the current DRC Ebola response, patients are naming an average of only five to eight contacts — a fraction of the expected range. And of those named contacts, only about half have actually been located by health workers.
That gap represents a significant vulnerability. Untraced contacts can seed new transmission chains in communities where health workers have no visibility, each one a potential origin point for further spread.
The contact tracing gap also has a structural explanation. When symptoms are mild, patients may not connect their illness to a recent Ebola exposure. They may attribute what feels like a routine illness to malaria or seek care from traditional healers or small health clinics with no capacity to test for Ebola. Some patients are arriving at larger treatment centers only when near death. Fear also plays a role: concerns about organ harvesting and the stigma of isolation keep some patients from seeking formal care at all.
A Fragile System Under Growing Pressure
The outbreak is compounding existing weaknesses in Congo’s health infrastructure. Treatment centers in Ituri Province are now better equipped, but response coordinators from organizations including the International Medical Corps and Doctors Without Borders have raised urgent concerns about North Kivu Province — particularly the cities of Beni and Butembo — where testing capacity is severely limited and supplies are scarce.
Health workers have borne a disproportionate burden. At least 18 have died, and some are believed to have contracted the virus earlier in the outbreak before it was formally identified — a sign of how long transmission may have been occurring undetected.
For global health security professionals, the Congo outbreak illustrates a paradox that challenges outbreak response doctrine: a less lethal pathogen is not necessarily a more containable one. When a disease produces milder illness, it can circulate longer in communities before triggering the alert signals that activate a response. By the time detection occurs, the chain of transmission may already be far wider and more diffuse than official case counts suggest — making the work of tracing, isolating, and stopping spread exponentially more difficult.
Sources and further reading:
Ebola Symptoms in Current Outbreak May Be Milder Than in Previous Ones – The New York Times