The outbreak of Ebola virus disease (EVD) in northeastern Democratic Republic of the Congo (DRC) continues. As of October 9, the outbreak has reached 194 total cases (159 confirmed, 35 probable; 122 deaths) with an additional 25 suspected cases under investigation. The current outbreak began in late July in DRC’s North Kivu province, mere days after another Ebola outbreak in the Equateur province was declared over. Recent reports note that the occurrence of new EVD cases has doubled since September, suggesting that control of that the outbreak may be worsening. In light of these reports, Outbreak Thursday attempts to track down evidence to assess the contact tracing and monitoring efforts in DRC—both of which are needed in order to contain the outbreak.

Overview of Current Situation in DRC

The October 4 Situation Report from WHO’s Regional Office for Africa (WHO/AFRO) the indicated that “control measures are largely working” but also warned against too much optimism, considering the challenges faced by responders on the ground—such as ongoing armed conflict in the area—and shortcomings in surveillance—such as the inability to adequately follow up with known contacts. The most recent WHO/AFRO Situation Report (October 9) notes that these challenges are reflected in the recent increase in cases—19 new confirmed cases and 21 new suspected cases since the October 4 report. Based on the available information, the extent to which new cases are being detected in individuals with no epidemiological links to known chains of transmission is uncertain. There is evidence, however, that cases are occurring in individuals who had not been previously identified or monitored, including some with no identified exposure to another known case. Additionally, the WHO recently increased its risk assessment for national and regional spread of the outbreak from “high” to “very high,” citing the security situation and the spread of the outbreak to areas near international borders. A recent STAT News report raises the possibility that the outbreak is poised to spiral out of control.

Ebola Surveillance

Even with the rapid deployment of investigational vaccines to support the response, this cannot, in and of itself, bring the outbreak under control. Identifying and following up with contacts of known cases can be a difficult task that is needed in order to contain Ebola outbreaks. Contact tracing, as this process is known, is a critical tool that enables health officials to actively monitor at-risk individuals, isolate cases before they can infect others, and project the potential scope and scale of the outbreak. Fortunately, Ebola is believed to only be transmissible after a patient begins displaying symptoms of the disease (eg, fever, fatigue, muscle pain or weakness). Additionally, Ebola is only transmitted via direct contact with infectious bodily fluids (eg, blood, feces, semen). These two factors simplify contact tracing efforts, as the pool of people who were potentially exposed to the virus is limited to individuals who had direct contact with a victim after the onset of symptoms.

Based on WHO/AFRO Situation Reports, it appears that responders are undertaking two kinds of contact tracing: prospective and retrospective. Prospective contact tracing refers to proactive efforts to identify and follow up with known contacts of new cases, whereas retrospective contact tracing focuses on identifying recent contacts of newly identified cases to identify potential sources of infection.

Both kinds of contact tracing identify contacts of new cases, but they serve different purposes. Retrospective contact tracing can help to identify potential sources of transmission for newly identified cases, including linking them to known chains of transmission. But in order to stay ahead of transmission, prospective efforts are critical. In order to interrupt transmission, health officials need to quickly identify contacts of new Ebola cases and actively monitor them for signs of disease, with the goal of quickly isolating anyone who becomes ill to reduce the probability that they will transmit to others. In the current EVD outbreak, a combination of prospective and retrospective contact tracing coupled with active monitoring is necessary to bring the outbreak under control. However, current reports suggest that responders have struggled to implement both kinds of surveillance, particularly the more resource-intensive prospective contact tracing and active monitoring approaches.

DRC Security Situation

Even in the best of circumstances, contact tracing can be a challenging endeavor, especially for diseases like Ebola that have associated stigma and fear that can make individuals hesitant to seek care or report potential exposures. In the current outbreak, transmission is ongoing in an area marred by armed conflict, which poses additional risks to responders, often preventing access to certain areas and potentially affected populations. In fact, all response activities, including contact tracing and community education were placed on hold in Beni as a result of the ongoing conflict. According to WHO/AFRO:

Field activities were severely limited in Beni during the week of 24 September 2018 following a community-led declaration of ‘ville morte’, a community-enforced general strike on all local activity. The declaration followed clashes between rebels and the Congolese armed forces, which took place on 22 September 2018. In solidarity with Beni, community leaders in Butembo and Mabalako Health Zones also declared a ville morte that severely limited Ebola response activities in those health zones. Consequently, the proportion of contacts followed-up in Beni fell to a low of 20% on the 23 September 2018.

The International Federation of the Red Cross/Red Crescent (IFRC) reported that a team of responders was recently “attacked while carrying out a safe and dignified burial,” illustrating both the direct threat to responders and the additional challenges of conducting education campaigns to promote safe burial practices that can prevent further transmission of Ebolavirus infection. The impact of the ongoing conflict on response operations is so substantial that WHO Director-General Dr. Tedros briefed the UN Security Council on the challenges responders are facing in the DRC. This briefing prompted the Security Council to issue a statement calling for the an end to the conflict to allow health officials to safely implement appropriate response activities.

Current Contact Tracing and Monitoring Efforts in DRC

Events such as the ville morte are likely to continue to impede response activities in the areas affected by the current outbreak, which is expected to further erode abilities to conduct prospective contact tracing and monitoring. The October 4 WHO/AFRO Situation Report notes that responders are having difficulty safely accessing affected areas due to ongoing conflict and security concerns. The ville morte that “followed clashes between rebels and Congolese armed forces” effectively halted all response efforts in Beni, Butembo, and Mabalako for a period of time. This stoppage resulted in the contact follow-up rate in Beni falling to a low of 20%. At that time, Beni represented 50% of the total known contacts in the current outbreak, and Mabalako represented another 20%. As of the October 9 Situation Report, the WHO/AFRO indicates that there are 2,115 total contacts currently being monitored. On October 7, follow-up was conducted with 2,013 (93%) of these individuals; however, 180 of the 202 outstanding contacts reside in Beni alone, which is a substantial population that could be at risk for developing EVD and transmitting the infection. Additionally, 40 known contacts have been classified as “lost to follow-up”—indicating that they have not participated in follow-up for a prolonged period of time and cannot be contacted. 37 of these individuals reside in Beni. On a positive note, 3 DRC refugees who were reported to be contacts of a deceased EVD victim were recently identified at a border crossing into Uganda, and all 3 are currently being monitored for the onset of symptoms, highlighting the importance of international collaboration and vigilance during these types of outbreaks.

Retrospective investigations are in progress for a number of recent confirmed cases to determine the source of infection. A number of recent cases were not previously identified as contacts of known cases, indicating that there are additional, unidentified infectious cases and chains of transmission that have not been detected through prospective contact tracing efforts. Notably, among the 35 probable cases identified since the onset of the outbreak, 27 are categorized as “community deaths” that were only identified after the victims had already expired. An additional 6 confirmed community deaths were reported by the DRC Ministry of Health over the past two days. These victims were determined to have died of EVD during a review of clinical records conducted after their deaths, indicating that they had not been identified through prospective efforts. Without being able to interview these patients, it is extremely difficult to determine the source of infection (via retrospective contact tracing) or monitor additional at-risk individuals (via prospective contact tracing). The inability to conduct necessary surveillance activities increases the likelihood that additional chains of transmission will remain undetected.


While there is some evidence that response efforts are limiting the spread of infection, the gaps in current surveillance and recent surge in cases indicate that there may be considerable transmission that is going unnoticed and unabated. Additionally, the difficulty in conducting follow-up and monitoring in affected areas like Beni severely hinders the ability of responders to bring the outbreak under control. Responders are facing an extremely challenging and dangerous situation in the DRC, and without a more complete picture of the ongoing chains of transmission, a major epidemic in the coming weeks and months is not out of the realm of possibility.

Photo: Scanning electron microscopic (SEM) image of filamentous Ebola virions (blue) budding from an infected cell (yellow-green). Photo courtesy of NIAID.

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly to allow others to learn from these experiences in order to improve global outbreak response capabilities.