Verdict: The outbreak was real, but there is no evidence that it was caused by a newly discovered “Disease X” pathogen.

In late 2024, health authorities in the Democratic Republic of the Congo investigated an unexplained outbreak in the Panzi Health Zone of Kwango Province. The illness was initially described as an undiagnosed disease and was sometimes referred to as “Disease X”. The reported cases included fever, headache, cough, difficulty breathing and other flu-like symptoms, with young children particularly affected.

The term “Disease X” itself does not identify a particular virus or newly discovered disease. The World Health Organization uses “Disease X” as a placeholder for a hypothetical future disease caused by a pathogen that is currently unknown but could cause a serious epidemic or pandemic. WHO has used the term in its pandemic-preparedness programme since 2018.

The situation in Panzi was nevertheless a genuine public-health investigation. Africa CDC sent experts to the Democratic Republic of the Congo in December 2024 to assist national authorities in identifying the cause of the outbreak and strengthening the response.

As laboratory investigations progressed, available evidence pointed toward known causes rather than confirmation of a novel pathogen. WHO reported that malaria was detected in tested patients, while further investigations identified common and seasonal respiratory infections. Severe acute malnutrition was also an important factor affecting the population, particularly children.

Later assessments therefore described the outbreak as most consistent with a combination of falciparum malaria, respiratory infections and acute malnutrition. This does not mean that every reported case had exactly the same cause, nor does it eliminate the importance of continued surveillance and laboratory investigation.

The key distinction is between the initially unexplained outbreak and the claim that a new pathogen called “Disease X” had been discovered. The first is supported by the contemporaneous reports from health authorities. The second was not established by the available evidence.

Conclusion: The Disease X investigation in the Democratic Republic of the Congo concerned a real outbreak of unexplained illness, but “Disease X” was not established as the name of a newly discovered pathogen causing the outbreak. Evidence available after the initial investigation pointed primarily to known infections, including malaria and respiratory infections, together with severe malnutrition.

Sources:

• WHO – Prioritizing diseases for research and development in emergency contexts
• WHO – Science in 5: Disease X
• Africa CDC – Investigation mission for Disease X in the DRC
• Journal of Public Health in Africa – Disease X in the Panzi region, DRC
• Scientific American – Mysterious Disease X outbreak