Michael Gwarisa
Health authorities are still searching for answers after a cluster of deaths and illnesses in Burundi that has so far defied diagnosis, despite extensive laboratory testing that has ruled out major viral haemorrhagic fevers such as Ebola and Marburg.
According to health officials involved in the investigation, hundreds of potential pathogens, including both viral and bacterial causes, have already been tested, yet the exact cause of the outbreak remains unknown.
Responding to a question from HealthTimes during the Africa CDC weekly media briefing, Professor Yap Boum, Deputy Incident Manager at Africa CDC, said investigations are ongoing in collaboration with Burundian health authorities and regional partners to determine the cause of the outbreak.
He noted that despite extensive testing, including more than 200 to 300 viral pathogens and multiple bacterial agents, no definitive cause has been identified.
“Let me take the opportunity to commend the country because they have done extensive diagnostics, testing more than 200 to 300 viruses on the viral side, and bacterial investigations as well, but the cause is still unknown,” said Professor Boum.
He added that investigators are now expanding the scope of analysis using a One Health approach, which considers possible interactions between human, animal and environmental health.
“There is quite a number of animals in that area, pigs, cattle and others. So there might also be the possibility of intoxication. We have seen this in other countries. That is also something we are looking at,” he said.
Experts caution that the absence of a confirmed diagnosis does not necessarily mean the outbreak is caused by a new or novel disease. They note that many infectious agents, environmental exposures, and limitations in sample quality and laboratory capacity can complicate early outbreak investigations.
Investigators are now broadening their scope to include advanced metagenomic testing and cross-border laboratory support, including collaboration with laboratories in the Democratic Republic of Congo.
Dr Mercy Kyeng, Epidemic Intelligence Unit Lead at Africa CDC, said it is too early to conclude that the outbreak is caused by a novel pathogen.
“And looking at the Burundi situation, it is really an interesting one. But again, ruling out para-haemorrhagic fevers does not in any way mean it is not an infectious disease. We have millions of infectious diseases out there with different strains,” she said.
Dr Kyeng said early diagnostic uncertainty is common in outbreak investigations, particularly where sample quality and laboratory conditions may affect results.
“So it is quite too early to say this is a novel pathogen. It could be because of the samples collected, maybe the quality of the samples, or the testing and all that,” she said.
She added that Burundi is now working with regional laboratories, including those in the Democratic Republic of Congo, to strengthen diagnostic capacity and improve testing accuracy.
“We saw clusters in households, of course speaking towards possible person-to-person transmission, but that still needs further investigation for us to be able to confirm that,” she said.
Dr Kyeng also noted that Burundi has not previously reported viral haemorrhagic fevers, although neighbouring countries have recorded such outbreaks, making regional surveillance important.
“There is still a lot of testing and investigation being done. Once that is made available, we are going to get back to you on the outcome,” she said, adding that Africa CDC is deploying experts to support laboratory diagnosis and outbreak response.
While the mystery deepens, health authorities stress that it is still too early to draw conclusions, underscoring the complexity of outbreak investigations and the challenges faced in identifying emerging health threats.
According to data presented by Professor Boum, the outbreak began on 30 March 2026 in Mpanda District, specifically in Rugazi and Kibuye zones. A total of 35 suspected cases and five deaths have been recorded, giving a case fatality rate of approximately 14 percent. Most cases are linked to a single household and close contacts.
Patients have presented with fever, vomiting, diarrhoea, headache and fatigue. Severe cases have included dark urine (haematuria), abdominal pain, jaundice, anaemia, neurological signs and respiratory distress.
Laboratory investigations have ruled out all tested viral haemorrhagic fevers, including Ebola, Marburg, Rift Valley fever, yellow fever and Crimean-Congo haemorrhagic fever. Both human and animal samples have been tested, but the cause remains unknown.
In response, health authorities have deployed multisectoral teams, strengthened case isolation and management, conducted active case finding and increased community sensitisation. Investigations are ongoing under a One Health approach integrating human, animal and environmental health surveillance.
