Congo Ebola cases jump as CDC warns outbreak could be among largest ever

Ebola cases in the Democratic Republic of Congo jumped by 71 in a day and another 21 deaths were recorded as health workers expanded testing in the mining town where the outbreak is believed to have begun, pointing to an epidemic that may be much bigger than previously understood.

The infections brought the number of laboratory-confirmed cases to 452 and deaths among confirmed patients to 82, according to a report released Friday by Congo's National Institute of Public Health. Health authorities have begun processing samples in Mongbwalu, an artisanal gold-mining center in Ituri province the epicenter of the outbreak, reducing delays in confirming suspected cases.

Researchers at the U.S. Centers for Disease Control and Prevention warned Friday that the Bundibugyo Ebola outbreak could become one of the largest Ebola epidemics ever recorded if control measures fail to accelerate. The epidemic's size when it was first detected suggests extensive undetected transmission, the agency said.

The outbreak has spread across more than two dozen health zones in three eastern Congolese provinces and into neighboring Uganda, where the number of confirmed cases increased by three Friday to 19. It is unfolding in a region marked by armed conflict, mass displacement, porous borders and fragile health systems, complicating efforts to identify cases and trace contacts.

The World Health Organization and the Africa Centres for Disease Control and Prevention launched a joint continental preparedness and response plan seeking about $319 million through November to support outbreak control in affected countries and strengthen readiness across neighboring nations. The final plan estimates total funding needs at $518 million.

Many confirmed patients developed symptoms between May 14 and May 23, followed by a second cluster of symptom onset between May 25 and June 3, health officials said. The pattern suggests the virus was continuing to spread in communities before the outbreak was formally recognized.

The finding aligns with a modeling analysis by the U.S. CDC. The high probability of a large outbreak stems primarily from the size of the epidemic at the time it was first detected rather than evidence that the virus is spreading unusually efficiently, the agency's researchers said in a study.

The outbreak "has the potential to quickly become one of the largest Ebola disease outbreaks ever recorded," they wrote.

The model suggested the outbreak may have originated from a spillover event in February, weeks before authorities were alerted to unexplained illnesses in Ituri. Depending on assumptions about the number of deaths that had already occurred by late May, the analysis estimated the most likely spillover date ranged from late January to mid-February.

Under a scenario in which only 20% of infected patients are rapidly identified and isolated, CDC projected a 65% chance that the outbreak could exceed 20,000 cases within three months. If roughly 70% of patients are isolated, only about one in 20 simulations resulted in outbreaks exceeding 10,000 cases.

Some response indicators have improved. The proportion of contacts successfully followed increased to 58% from 46% two days earlier, while nearly 4,800 contacts are now under monitoring. Health authorities also reported that a new diagnostic laboratory installed in Mongbwalu is bringing testing capacity closer to affected communities.

Containment efforts continue to face obstacles. The International Red Cross and Red Crescent Movement condemned an attack on volunteers carrying out a safe burial operation in Bunia, saying Friday that several responders were injured. "Attacks against volunteers not only endanger lives, they also undermine efforts to contain the outbreak and protect communities," the organization said.

Unlike the Zaire strain responsible for most major Ebola epidemics, there is no licensed vaccine or approved therapy specifically for Bundibugyo virus disease, though several experimental vaccines and treatments are under development.

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