Many cases of mpox in DRC thought to be false diagnoses, say Swiss researchers

Mpox: many cases in the DRC are thought to be false diagnoses (UNIGE) Keystone-SDA

More than a third of mpox cases in the DRC are thought to be linked to the contamination of samples from their surroundings rather than a genuine infection, say University of Geneva researchers who analysed more than 2,700 test results.

According to a study done by several institutions, including the University of Geneva, published in The Lancet Infectious Diseases journal, nearly 35% of the samples were found to be contaminated with mpox viral DNA. These tests, carried out between April 2024 and April 2026, were conducted in the cities of Goma, Kamituga, Kinshasa and Uvira in the Democratic Republic of the Congo (DRC).

In August 2024, the World Health Organization (WHO) declared the outbreak a public health emergency of international concern, before lifting this alert in September 2025. Mpox is characterised by fever and skin rashes that can cause painful and disfiguring lesions. In some cases, it can be fatal. Between 2024 and 2026, more than 120,000 cases and around 1,500 deaths were recorded in Africa.

Rapid identification of the virus is important for targeting vaccination and organising public health measures, the University of Geneva said on Tuesday. The researchers were surprised by the presence of two distinctly different groups at the four sites.

DNA present for weeks

The first group showed low levels, indicating a high viral load. The second, meanwhile, barely reached the detection threshold, suggesting the presence of residual viral traces.

The international team then took samples from surfaces at two healthcare centres. Many of these samples tested positive. As mpox DNA can remain on surfaces or in the air for several weeks, it was probably detected by mistake in subsequent results, the university said.

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In a separate approach, serological data were analysed. Around 89% of those classified as false positives had no antibodies against the virus, proving that they had not been infected.

Another significant study

In a separate study, researchers tested suspected cases to assess their exposure to other viruses that cause skin rashes. Most were carrying other infections, with only a small proportion actually infected with mpox.

These false diagnoses have real implications for public health and patients, according to the university. Unnecessary treatment was provided, and quarantine measures were imposed on people who should not have been subject to them.

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Among the solutions, “the PCR positivity threshold needs to be lowered” to significantly reduce false positives without substantially increasing false negatives, explains the associate professor at the university who led the research team. The institution is collaborating with the WHO to improve virus detection in several countries.

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Translated from French, reviewed by an English Department journalist.