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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.

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.

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.

NEW YORK — No quick dispatching of disease investigators. No televised news conference to inform the public. No timely health alerts to doctors.

In the midst of a hantavirus outbreak that involves Americans and is making headlines around the world, the U.S. government’s top public health agency, the Centers for Disease Control and Prevention, has been uncharacteristically missing in action, according to a number of experts.

To President Trump, “we seem to have things under very good control,” as he told reporters Friday evening.

To experts, the situation aboard a cruise ship has not spiraled because, unlike COVID-19 or measles or the flu, hantavirus does not spread easily. It has been health experts in other countries, not the United States, who have been dealing primarily with the outbreak in the last week.

“The CDC is not even a player,” said Lawrence Gostin, an international public health expert at Georgetown University. “I’ve never seen that before.”

Not until late Friday did CDC actions accelerate.

Health officials confirmed the deployment of a team to Spain’s Canary Islands, where the ship was expected to arrive early Sunday local time, to meet the Americans onboard. They said a second team will go to Offutt Air Force Base in Nebraska as part of a plan to evacuate U.S. passengers from the ship to a University of Nebraska quarantine center for evaluation and monitoring. Also, the CDC issued its first health alert to U.S. doctors, advising them of the possibility of imported cases.

At their first briefing, held Saturday by telephone only for invited reporters, officials pledged to be transparent in updating the public but said the media could not cite the speakers by name under rules set by aides to Health Secretary Robert F. Kennedy Jr. They did not directly answer a question about whether the U.S. passengers could leave the university medical facility when they wanted.

The CDC’s diminished role in this outbreak is an indicator the agency is no longer the force in international health or the protector of domestic health that it once was, some experts said.

The hantavirus outbreak is “a sentinel event” that speaks to “how well the country is prepared for a disease threat. And right now, I’m very sorry to say that we are not prepared,” said Dr. Jeanne Marrazzo, chief executive officer of the Infectious Diseases Society of America.

How the outbreak unfolded

Early last month, a 70-year-old Dutch man developed a feverish illness on a cruise ship traveling from Argentina to Antarctica and some islands in the South Atlantic. He died less than a week later. More people became sick, including the man’s wife and a German woman who both died.

Hantavirus was first identified as a cause of sickness of one of the cases on May 2. The World Health Organization swung into action and by Monday was calling it an outbreak. About two dozen Americans were on the ship, including about seven who disembarked last month and 17 who remained on board.

It’s WHO taking center stage

For decades, the CDC partnered with the WHO in such situations. The CDC acted as a mainstay of any international investigation, providing staff and expertise to help unravel any outbreak mystery, develop ways to control it and communicate to the public what they should know and how they should worry.

Such actions were a large reason why the CDC developed a reputation as the world’s premier public health agency.

But this time, the WHO has been center stage. It made the risk assessment that has told people the outbreak is not a pandemic threat.

“I don’t think this is a giant threat to the United States,” said Jennifer Nuzzo, director of Brown University’s Pandemic Center. But how this situation has played out “just shows how empty and vapid the CDC is right now,” she said.

Tumult under Trump

The current situation comes after 16 tumultuous months during which the Trump administration withdrew from the WHO, has restricted CDC scientists from talking to international counterparts at times and embarked on a plan to build its own international public health network through one-on-one agreements with individual countries.

The administration has laid off thousands of CDC scientists and public health professionals, including members of the agency’s ship sanitation program.

As this was playing out, Kennedy said he was working to “restore the CDC’s focus on infectious disease, invest in innovation, and rebuild trust through integrity and transparency.”

Waiting to hear from the CDC

The CDC has not been completely silent on hantavirus.

The agency on Wednesday issued a short statement that said the risk to the American public is “extremely low,” and described the U.S. government as “the world’s leader in global health security.”

Said Nuzzo: “Not only was that not helpful, it actually does damage because a core principle of public health communications is humility.”

The CDC’s acting director, Dr. Jay Bhattacharya, posted a message on social media that the agency was lending its expertise in coordinating with other federal agencies and international authorities. Arizona officials this week said they learned from the CDC that one of the Americans who left the ship — a person with no symptoms and not considered contagious — had already returned to the state. WHO officials said the CDC has been sharing technical information.

The CDC also is “monitoring the health status and preparing medical support for all of the American passengers on the cruise,” Bhattacharya wrote.

But federal health officials have mostly been tight-lipped, declining interview requests.

COVID-19 comparison

In interviews this week, some experts made a comparison with a 2020 incident involving the Diamond Princess, a cruise ship docked in Japan that became the setting of one of the first large COVID-19 outbreaks outside China.

The CDC sent personnel to the port, helped evacuate American passengers, ran quarantines, shared genetic data on the virus, coordinated with the WHO and Japan, held public briefings and rapidly published reports “that became the world’s reference data on cruise ship COVID transmission,” said Dr. Tom Frieden, a former CDC director.

Some aspects of the international response to the Diamond Princess were criticized, and it did not halt the outbreak or stop COVID-19’s spread across the world. But some experts say it was not for the CDC’s lack of trying.

“The CDC was right on top of it, very visible, very active in trying to manage and contain it,” Gostin said, while the agency’s work now is delayed and subdued.

Instead of working with nearly all of the world’s nations through the WHO, the Trump administration has pursued bilateral health agreements with individual nations for information sharing, public health support, and what it describes as “the introduction of innovative American technologies.” Roughly 30 agreements are currently in place.

That’s not sufficient, Gostin said. “You can’t possibly cover a global health crisis by doing one-on-one deals with countries here and there,” he said.

Stobbe writes for the Associated Press. AP writers Ali Swenson in New York, Darlene Superville in Washington and Susan Montoya Bryan in Albuquerque contributed to this report.