Poisoning or bacterial meningitis could be behind dozens of mysterious deaths in the Democratic Republic of the Congo

The World Health Organization (WHO) suspects that poisoning or meningitis could explain a mysterious illness that has reportedly killed 53 people in the Democratic Republic of the Congo.

The unidentified illness has impacted people in the northwestern province of Equateur. Since Feb. 9, when the first cases were reported, health authorities have recorded more than 1,300 patients that meet the "suspected case definition" of the disease.

This new cluster of illnesses and deaths follows another one reported in January, which affected 12 people and resulted in eight fatalities. Both of these outbreaks occurred in the Equateur province, but the WHO has determined that they are separate events with different causes.

The reported symptoms tied to the latest outbreak are broad, including fever, chills, headaches and other symptoms seen in common diseases, such as malaria, so the "trends in cases are difficult to interpret," according to a WHO report published Monday (Mar. 3).

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The WHO suggested that malaria could be in part to blame for the cases, but hypothesized that an "accidental or deliberate" chemical poisoning or bacterial meningitis — a life-threatening brain infection — might explain the unusual deaths.

"The definitive cause of illness remains undetermined," the WHO report notes. However, current evidence suggests a downward trend in the number of fatalities since the first deaths were reported on Feb. 9; the most recent death was recorded on Feb. 22. The illnesses also seem to be clustered geographically, with most deaths confined to one village, called Bomate, so it doesn't appear to be spreading based on the evidence currently available.

"The majority of deaths (50) occurred in the same village," the WHO report states. "Furthermore, the incidence of death rapidly declined following the initial cluster, suggesting this is not an event spreading in time or place."

Two clusters

Mysterious illnesses were initially flagged in three young children in a village called Boloko. Between Jan. 10 and Jan. 13, the children died after reportedly eating a bat. More cases were then reported, infecting many more people and killing a total of eight across Boloko and the nearby village Danda, Live Science previously reported.

Then, on Feb. 9, a second cluster of 24 unexplained deaths was reported in the village of Bomate, also in Equateur. This second cluster has become the focus for health officials, and 53 total deaths have been reported there as of Feb. 25.

The WHO has determined that the two clusters were separate events with no evidence linking them together.

While both outbreaks are "located within Equateur Province, these health zones are separated by approximately 175 kilometers of difficult terrain including dense forests and poor road infrastructure," the report says. "Epidemiological investigation has found no evidence linking these distinct events." Lab testing suggested that severe malaria may have been behind the first cluster in Boloko and Danda, according to the report.

To investigate the second cluster, local authorities began monitoring any individual with fever and at least one other symptom in the area. A total of 1,318 people had symptoms meeting that definition between Feb. 9 and Feb. 25.

However, their symptoms were so broad that WHO concluded that the number of cases probably reflected a range of fever-related illnesses that are always present in the community. About half of those presenting symptoms also tested positive for malarial parasites, "which is not deemed unusual in an area where malaria is hyperendemic."

Unusual deaths

The 53 deaths have affected all age groups but appear to have disproportionately hit adolescent and young males. That's unusual because, typically, deaths within the community are spread across both sexes and the highest rates are seen among older adults and young children, according to the report.

WHO still has a lot to learn about the deaths and why young males were particularly badly hit. For now, a "rapid onset of bacterial meningitis" has been raised as a possible cause. Meningitis is an infection of the meninges, which are protective membranes that cover the brain and spinal cord. The bacterial form of the disease has the potential to kill within hours, according to the Cleveland Clinic.

Health officials are continuing to investigate the source of the mysterious illness and are collecting water and other environmental samples to explore the potential for poisoning from chemical contamination, according to the report.

WHO determined that the illness presents a "moderate" public health risk at the local level but that the national and global public health risk remains low.