Impact of Detection-Isolation-Leakage on the 2026 DRC Bundibugyo Ebolavirus Outbreak

Abstract

Abstract The 17th Ebola outbreak in the Democratic Republic of the Congo, announced on 15 May 2026, was attributed to Bundibugyo ebolavirus (BDBV). Although case isolation is the main control strategy, its effectiveness is compromised when patients escape isolation facilities before recovery. Between 14 May and 17 June 2026, 175 individuals reportedly left isolation facilities without formal discharge across Ituri Province. We assessed how this “isolation leakage” affects community transmission. We refined the SEIHFR framework to distinguish undetected community infections, detected but not-yet-isolated cases, isolated individuals, leakage, funeral-associated transmission, and removals. Using Bayesian inference, we fitted the model to daily Ituri surveillance data, escapee counts, and isolation census records. We estimated the leakage rate, reporting and detection probabilities, and the transmission rate, while fixing other parameters based on the BDBV literature. The model reproduced confirmed cases, deaths, discharges, and escapees. We estimated R 0 = 3.67 (95% HDI: 2.0–5.7), a leakage rate of ρ ≈ 0.034 day − 1 (0.022–0.051), and high contact-tracing-driven detection ( p d ≈ 0.91–0.99). Leakage increased the detection-dependent reproduction number R ( p d ) from approximately 3.2 to above 5. Eliminating leakage reduced cumulative infections by about one-third, from 1,120 to 764, while the minimum detection level required for control increased from p d ≥ 0.73 without leakage to p d ≥ 0.87 at the fitted leakage rate. Shortening time to isolation prevented the most infections (73.4%; 59–84), followed by reducing leakage (29.7%; 14–52) and re-isolating escapees (12.6%; 6–24). Delaying leakage reduction until week 4 reduced its benefit from about 27% to below 2%. Isolation leakage represents a major transmission pathway that has until now gone largely unmeasured. While rapid initiation of isolation is highly beneficial, it cannot compensate for permeable isolation; therefore, early, community-driven efforts to control leakage, embedded within a multilayered response, are critical. Author Summary In 2026, an Ebola outbreak caused by the Bundibugyo virus emerged in the northeastern Democratic Republic of the Congo. Since there is no vaccine or approved treatment for this strain, health workers must depend on rapid case detection, prompt isolation, and safe burials to halt transmission. However, surveillance data highlighted a persistent challenge: many patients escaped isolation centers before fully recovering and returned to their communities while still contagious. We refer to this as “isolation leakage.” Although frequently reported during Ebola outbreaks, it has rarely been analyzed using mathematical modeling. We developed a model that follows undetected infections in the community, patients in isolation, and those who escape isolation, and calibrated it to daily surveillance data from Ituri Province, including daily counts of people who escaped Ebola isolation centers. Our analysis showed that leakage significantly amplified the size of the outbreak, and that early action was crucial; intervening to reduce leakage in the first week averted far more infections than waiting until a month into the outbreak. Shortening the time to isolation was the most effective single intervention. These findings indicate that ensuring patients remain in care is vital for controlling the 2026 Ebola outbreak in the fragile, conflict-affected region of Eastern DRC.