The Ebola Outbreak Hidden by a Faulty Test: WHO Declares Global Emergency as Cases Reach Kampala

The Democratic Republic of Congo had been experiencing an Ebola outbreak for nearly three weeks before the world knew it. By the time laboratory tests confirmed the virus in Ituri province on May 15, approximately 80 people had already died and 246 suspected cases were on record. Field diagnostic machines had been testing samples the whole time — and returning negative results, because they were calibrated to detect a different Ebola species entirely.

On Sunday morning, WHO Director-General Tedros Adhanom Ghebreyesus declared the outbreak a Public Health Emergency of International Concern — the highest alarm level the World Health Organization can issue. Cases have now been confirmed in two countries. On May 15, a 59-year-old Congolese man who had traveled from Ituri province died at Kibuli Muslim Hospital in Kampala, Uganda. A second confirmed case in Kampala followed May 16. A third confirmed case, also linked to travel from Ituri, appeared in Kinshasa — the DRC capital of 17 million — the same day.

The total stands at 11 laboratory-confirmed cases across two countries, and 246 suspected cases in Ituri. The scale of the suspected-case count against the number of confirmed cases reflects a fundamental problem: the Ebola variant driving this outbreak is not the one health systems on the ground were built to find.

The GeneXpert diagnostic machines used in Ituri province are calibrated to detect the Zaire strain of Ebola — the strain responsible for all 16 previous DRC outbreaks and the 2014-2016 West African epidemic that killed more than 11,000 people. The current outbreak is caused by Bundibugyo virus, a distinct species within the Ebola genus that is genetically approximately 40 percent different from Zaire.

A GeneXpert test designed for Zaire will return a negative result for a Bundibugyo-positive sample. Health workers in Ituri were testing, getting negatives, and ruling Ebola out while the outbreak grew.

It was only when samples reached the Institut National de Recherche Biomédicale in Kinshasa — where broader species detection is possible — that the outbreak was confirmed. By that point, the first suspected case had likely appeared around April 24, when a nurse with fever, vomiting, severe weakness, and bleeding symptoms died at the Evangelical Medical Center in Bunia, Ituri’s capital. That nurse is believed to be the index case.

Jean-Jacques Muyembe, the Congolese virologist who co-discovered Ebola in 1976 and now heads the INRB, told Reuters the identification of a non-Zaire variant “will complicate the response, as existing treatments and vaccines were developed against the Zaire strain.” Muyembe noted that all but one of Congo’s previous 16 outbreaks had been caused by Zaire. The Bundibugyo variant has been documented only twice before, ever.

No Vaccine. No Treatment.

This is the element that makes the 2026 Bundibugyo outbreak categorically different from the last several Congo Ebola responses.

The two licensed Ebola vaccines — Ervebo (rVSV-ZEBOV) and the two-dose Zabdeno/Mvabea combination — protect against Zaire strain only. The two licensed monoclonal antibody therapeutics — Inmazeb and Ebanga — were developed against Zaire. None of them work against Bundibugyo.

DRC Health Minister Samuel Roger Kamba Mulamba said the Bundibugyo strain “has a very high lethality rate which can reach 50 percent” and confirmed “The Bundibugyo strain has no vaccine and no specific treatment.” Medical care is supportive: fever management, fluid replacement, and intensive care for patients who deteriorate. Historical case fatality rates across the two previous Bundibugyo outbreaks ranged from 25 percent to 51 percent.

The first documented Bundibugyo outbreak occurred in western Uganda in 2007-2008, producing 149 cases and 37 deaths. The second hit eastern Congo in 2012, with 57 cases and 29 deaths. Experts at Imperial College London told Science/AAAS that the 2026 outbreak is “likely already the largest documented Bundibugyo outbreak” given that its suspected case count in Ituri alone already exceeds both previous outbreaks combined.

The Imperial College team also assessed that the outbreak “has likely gone undetected and spread for several weeks or even months” — a judgment that tracks with the three-week gap between the probable index case and official confirmation.

A Conflict Zone With High Population Movement

Ituri province presents some of the hardest operating conditions on the continent for an outbreak response. Armed groups including the Allied Democratic Forces — affiliated with ISIS — and the CODECO militia have been active in the region. Congolese army forces have been redeployed to counter M23 in eastern Congo, thinning security coverage in Ituri. The U.S. State Department has rated Ituri at its highest travel danger level, Level 4, and has stated it is unable to provide emergency services to U.S. citizens in the province.

The three health zones where confirmed DRC cases are concentrated — Bunia, Rwampara, and Mongwalu — are all relatively urban with high population movement. Mongwalu is a mining town; Bunia is a provincial capital. That mobility, combined with the diagnostic gap that allowed the outbreak to build undetected, is what produced confirmed cases in both Kampala and Kinshasa within 24 hours of each other on May 15-16.

Jennifer Nuzzo, director of the Pandemic Center at Brown University’s School of Public Health, described the situation’s scale as “pretty stunning.” “It’s possible that we’re starting to see the consequences of severe and sudden cuts to global health programs that have eroded surveillance and allowed deadly viruses to spread undetected,” she told reporters.

This outbreak joins a growing list of infectious disease events in 2026 that have required international coordination. American Courant’s coverage of the Andes hantavirus outbreak aboard the MV Hondius documented a parallel case of a virus spreading through a closed population — killing three people and placing 18 Americans in federal quarantine — before a diagnosis was confirmed.

What WHO’s Emergency Declaration Does

Tedros’s PHEIC declaration on Sunday was unusual in one procedural respect: he invoked Article 12 of the International Health Regulations directly, without first convening a formal Emergency Committee — an atypical sequence. The WHO said it would convene an Emergency Committee “as soon as possible” after the declaration to advise on temporary recommendations.

“After having consulted the DRC and Uganda where the Ebola disease caused by Bundibugyo virus is known to be currently occurring, I determine that the epidemic constitutes a public health emergency of international concern, as defined in the provisions of IHR,” Tedros said in the official WHO statement. He stressed the outbreak “does not meet the criteria of pandemic emergency” and advised all countries not to close their borders or impose travel or trade restrictions, calling such measures unscientific.

A PHEIC declaration unlocks emergency funding and coordination mechanisms and requires countries to report new cases through official WHO channels. The WHO issued initial temporary recommendations including: isolating all confirmed cases, daily contact monitoring, activating emergency management systems in affected countries, and cross-border screening at key entry points.

The CDC has issued a Level 1 (Practice Usual Precautions) Travel Health Notice for Uganda and issued health alerts through the U.S. Embassy in Kampala on May 15. Acting CDC Director Jay Bhattacharya said the agency has country offices in both DRC and Uganda and is coordinating response support. “The risk to the American public is considered low,” Bhattacharya said.

Africa CDC convened an urgent high-level regional coordination meeting on May 16 with DRC, Uganda, South Sudan, the WHO, UNICEF, the Pandemic Fund, and other partners — acknowledging the cross-border exposure and the specific challenges posed by an outbreak that can’t be detected by the diagnostic equipment already deployed in the field.

What Happens Next

The immediate question is whether the two Kampala cases represent contained travel-linked exposures or early local transmission. As of Sunday, Ugandan health authorities had not confirmed locally transmitted cases — both confirmed Uganda cases had traveled from DRC. The same is true of the Kinshasa case. WHO contact tracing teams are tracking all known contacts of all confirmed cases.

The diagnostic gap is being addressed on an emergency basis. INRB in Kinshasa is the current reference laboratory for Bundibugyo confirmation. The WHO is working with partners to expand testing capacity closer to Ituri. With no vaccine to deploy and no treatment to administer, isolation and contact tracing carry the full burden of containment — the same approach used in every pre-Ervebo Ebola response.

The CDC’s broader capacity challenges in 2026 — including the ongoing U.S. measles outbreak that has put the country’s 25-year elimination status under review — add context to why global surveillance gaps are drawing attention from public health researchers. Bhattacharya noted the CDC has “extensive experience and expertise” in Ebola response and affirmed it is providing active support to DRC and Uganda through in-country offices.

This is the 17th recorded Ebola outbreak in the Democratic Republic of Congo since the virus was first identified in 1976. It is the first in Congolese history caused by the Bundibugyo strain. And it is the first Ebola outbreak of any kind to reach Kampala since the city faced a separate Ebola incident in 2022.

Whether it stays contained will depend almost entirely on contact tracing working faster than the virus.