Cluster of community deaths in Basankusu, Equateur- Democratic Republic of the Congo

On 9 February 2025, officials in the Democratic Republic of the Congo reported to regional health authorities a cluster of 24 unexplained community deaths in a single village in Ekoto health area, Basankusu health zone, Equateur province. As of 25 February, a total of 53 deaths have been reported, with the last death occurring on 22 February. Deaths have occurred in all age groups, but adolescents and young adults, particularly males, appeared to be disproportionately affected in the initial cluster reported. Disease progression appeared to be fast, with a median time from onset of symptoms to death of one day. Given the rapid decline in the incidence of reported deaths, their geographic clustering, the age profile of deaths and the rapid disease progression in the initial cluster, working hypotheses include chemical poisoning or a rapid onset bacterial meningitis cluster, on a background of malaria and other infectious illnesses endemic in the region. The definitive cause of illness remains undetermined, with initial samples testing negative for Ebola and Marburg viruses. Field investigations and additional laboratory testing are ongoing including but not limited to the cerebrospinal fluid testing and the toxicological analysis of environmental samples, including water and other samples to explore chemical causes. Local authorities began surveillance with a broad case definition including any individual with fever and at least one other symptom, to better understand disease patterns. A total of 1318 patients had symptoms meeting the working suspected case definition as of 25 February 2025. Approximately 50% of malaria tests performed on these cases tested positive for malaria, the cases identified through this enhanced surveillance therefore likely reflect the various febrile illnesses in the area. With the available information, WHO assesses the local public health risk as moderate, and the national and global public health risk as low.

On 9 February 2025, an initial cluster of 24 community deaths of unknown origin were reported from a single village in Ekoto Health Area, Basankusu Health Zone, Equateur province, in the Democratic Republic of Congo. This triggered an investigation by the Ministry of Health, supported by WHO.

Enhanced surveillance was implemented shortly after, using a broad working case definition given the limited details on the clinical presentation, disease progression, demographic and other characteristics of the initial cluster. As of 25 February, a total of 53 deaths were reported (Figure 1). Deaths occurred across all age groups, but compared to the age and sex distribution of the population, appeared to disproportionately affect adolescents and young adult males, particularly in the initial cluster (Figure 2). This further pointed to an unusual event, as mortality from common causes in the area is usually highest among the elderly, and among young children (under five years) in a context of a high burden from infectious diseases, including malaria. The majority of deaths (50) occurred in the same village (Figure 3). Furthermore, the incidence of death rapidly declined following the initial cluster (Figure 1), suggesting this is not an event spreading in time or place.

The preliminary findings of the in-depth analysis revealed that the median time from symptom onset to death in the initial cluster was one day, with a mean time of two days. Symptoms reported include fever, chills, headaches, muscle aches, abdominal pains, diarrhea, sweating, dizziness, shortness of breath, agitation, and others.

Figure 1: Epidemic curve showing deaths reported between 9 February and 25 February 2025, Basankusu health zone, Democratic Republic of the Congo. * 

*Based on the line list available for deaths (n=53) as of 25 February 2025

Figure 2: Age-sex distribution of cases and deaths reported between 9 February to 25 February 2025, Basankusu health zone, Democratic Republic of the Congo. 

Figure 3: Geographic distribution of all cases (left) and deaths (right) reported between 9 February and 25 February 2025, Basankusu health zone, Democratic Republic of the Congo*

*Based on the line list available for suspected cases (n=1198) as of 25 February 2025

Since the initiation of enhanced surveillance,1318 people reported symptoms meeting the working suspected case definition. However, given the broad nature of the case definition (fever and one other symptom from a range of general respiratory, gastrointestinal, or neurological symptoms), the trends in cases are difficult to interpret, and most likely reflect the prevalence of a range of febrile illnesses in the community. This is further suggested by the age distribution broadly mirroring that of the population (Figure 2), and the high malaria positivity among cases that were tested (approximately 50% positive on rapid diagnostic tests), which is not deemed unusual in an area where malaria is hyperendemic.

Figure 4: Epidemic curve showing suspected cases reported between 9 February to 25 February 2025, Basankusu health zone, Democratic Republic of the Congo. *

*Based on the line list available for suspected cases (n=1198/1318) as of 25 February 2025

Although the cases were initially identified using a broad (i.e. non-specific) case definition, given the localized nature of the cluster of deaths, the steady decline in incidence of deaths, the demographic profile of deaths, and the rapid disease progression in the initial cluster, working hypotheses are that of a contamination by a chemical poisoning–be it accidental or deliberate—or possibly a rapid onset bacterial meningitis cluster.

Initial laboratory test results released on 13 February 2025 were negative for both Marburg and Ebola. Additional samples (blood, urine, oral, nasal) have been collected for further testing and investigations are ongoing. In addition, environmental samples–including water and other samples–are being collected to explore chemical causes, such as contamination by organophosphates.

The definitive cause of illness remains undetermined. Further testing and field investigations are ongoing to better characterize the cases and deaths.

Of note, this event in Basankusu follows a recent cluster of community deaths in the Bolomba Health Zone, which occurred from 10 to 27 January 2025. The epidemiological investigation documented 12 cases with eight deaths. Laboratory testing excluded Ebola and Marburg virus diseases and suggested that severe malaria could be the cause. While both Bolomba and Basankusu are located within Equateur Province, these health zones are separated by approximately 175 kilometers of difficult terrain including dense forests and poor road infrastructure; epidemiological investigation has found no evidence linking these distinct events.

• Coordination: A provincial rapid response team deployed to Basankusu and arrived on 16 February. The team was further supported by a WHO-MoH team from Kinshasa which arrived on 23 February.
  
• Surveillance: WHO is supporting the MoH teams with field investigations, including the development of a structured epidemiological investigation protocol and the collection of additional samples for testing. As surveillance is being scaled up, the focus is on better understanding the characteristics of deaths. WHO is supporting health teams in their case investigations and active case search in the affected areas, including in communities, churches, and health facilities.                                                                              
• Laboratory: WHO is providing laboratory support to guide proper collection, storage, and transport of collected specimens to the National Institute of Biomedical Research (INRB) in Kinshasa, the biggest and most equipped laboratory in the country.
  
• Logistics: WHO has provided essential medical supplies for management of usual infectious diseases and their symptoms, laboratory testing and infection prevention and control (IPC).
  
• Risk communication and community engagement: Community engagement efforts are ongoing. Training sessions for community health workers are being conducted on how to identify people who meet the case definition and perform disease surveillance reporting. Awareness activities include community briefings and local radio broadcasts, as well as targeted discussion in villages on care-seeking behavior. 
  
• Infection prevention and control: Systematic decontamination of isolation rooms at the General Hospital in Basankusu and Ekoto Health Center have been performed. On-site training of IPC supervisors and hygienists on chlorine solution preparation for decontamination have been conducted.

Since the initial cluster of deaths was reported on 9 February 2025, there has been an overall downward trend in deaths. The most recent death was reported on 22 February 2025. Current epidemiological information suggests a localized event with a steady decline in incidence, not expanding in time and place. Given the clinical presentation of deaths and the speed from symptom onset to death in this unusual cluster, current differentials include a rapid onset bacterial meningitis cluster or a contamination by a chemical poisoning as key hypotheses in a context of high incidence of other common infectious diseases in the areas, particularly malaria.

Operational challenges related to this event involve the isolation of Basankusu and resulting logistical barriers, as it is located in a forested region, approximately 450 kilometers from the nearest major city of Mbandaka and has poor infrastructure. The remoteness of Basankusu has hindered the timeliness of the initial investigation and response activities and poses challenges to laboratory testing. Samples must be collected, stored, and shipped long distances to a larger city with laboratory testing capacity (either Mbandaka or Kinshasa), introducing delays in diagnosis. Access to care is another key challenge, as the region lacks robust healthcare services, and the region’s poor infrastructure makes travel to neighboring health zones difficult, leading to delays in treatment.  

The province faces a severe urban water crisis with only 5% of its urban population having access to drinking water. The water network suffers frequent leaks and has never been rehabilitated. Many households rely on unregulated private water sources such as wells, springs and streams which pose contamination risks.

With ongoing investigations and given that the causative agent of the cluster is not yet determined, there remains a level of risk attributed to the event. As such, the overall public health risk level to the affected communities is assessed as moderate.

At the national level, however, the risk is considered low due to the localized nature of the event and apparent decreasing incidence. Similarly, at the regional and global levels, the risk is low at this time. 

To reduce the impact of the event in the Basankusu health zone, WHO advises the following measures:  

• Careful characterization of the clinical syndrome and outcomes as well as an improved case definition based on collected information to better understand the outbreak.
• Enhanced surveillance focusing specifically on deaths, and severe febrile cases or severe cases of unexplained illness, with better clinical characterization to reinforce early case detection and reporting.
• Continued laboratory testing and environmental assessments (including water sources) to evaluate the current hypotheses of meningitis and/or a toxin/poisoning event, particularly among severe cases and deaths.
• Risk communication and community engagement to increase public awareness about the event, explaining symptoms and the importance of seeking immediate care. It is also critical to address any potential misinformation about the outbreak circulating in the community.
  

Citable reference: World Health Organization (3 March 2025). Disease Outbreak News; Cluster of community deaths in Basankusu, Equateur, the Democratic Republic of the Congo. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON557