Drivers of the dynamics of the spread of cholera in the Democratic Republic of the Congo, 2000–2018: An eco-epidemiological study

Background: The dynamics of the spread of cholera epidemics in the Democratic Republic of the Congo (DRC), from east to west and within western DRC, have been extensively studied. However, the drivers of these spread processes remain unclear. We therefore sought to better understand the factors associated with these spread dynamics and their potential underlying mechanisms. Methods: In this eco-epidemiological study, we focused on the spread processes of cholera epidemics originating from the shores of Lake Kivu, involving the areas bordering Lake Kivu, the areas surrounding the lake areas, and the areas out of endemic eastern DRC (eastern and western non-endemic provinces). Over the period 2000–2018, we collected data on suspected cholera cases, and a set of several variables including types of conflicts, the number of internally displaced persons (IDPs), population density, transportation network density, and accessibility indicators. Using multivariate ordinal logistic regression models, we identified factors associated with the spread of cholera outside the endemic eastern DRC. We performed multivariate Vector Auto Regressive models to analyze potential underlying mechanisms involving the factors associated with these spread dynamics. Finally, we classified the affected health zones using hierarchical ascendant classification based on principal component analysis (PCA). Findings: The increase in the number of suspected cholera cases, the exacerbation of conflict events, and the number of IDPs in eastern endemic areas were associated with an increased risk of cholera spreading outside the endemic eastern provinces. We found that the increase in suspected cholera cases was influenced by the increase in battles at lag of 4 weeks, which were influenced by the violence against civilians with a 1-week lag. The violent conflict events influenced the increase in the number of IDPs 4 to 6 weeks later. Other influences and uni- or bidirectional causal links were observed between violent and non-violent conflicts, and between conflicts and IDPs. Hierarchical clustering on PCA identified three categories of affected health zones: densely populated urban areas with few but large and longer epidemics; moderately and accessible areas with more but small epidemics; less populated and less accessible areas with more and larger epidemics. Conclusion: Our findings argue for monitoring conflict dynamics to predict the risk of geographic expansion of cholera in the DRC. They also suggest areas where interventions should be appropriately focused to build their resilience to the disease. Author summary: Cholera is considered endemic in the eastern part of the Democratic Republic of the Congo (DRC), along the Great Lakes Region. From these endemic areas, cholera outbreaks regularly spread to other areas. However, some major epidemics have spread to far-off areas outside the endemic eastern DRC. Although the dynamics of their spread have been widely described, their underlying mechanisms are still unclear. Our modelling framework showed that the exacerbation of conflict events, followed by mass population movement and the amplification of cholera outbreaks in endemic areas bordering Lake Kivu, significantly increased the risk of spatio-temporal spread of major cholera epidemics outside the endemic eastern provinces of DRC. In addition, we found that the remote areas affected by these major epidemic waves were grouped into three categories based on cholera indices, population density, transportation network density, and geographic accessibility. Monitoring of conflict dynamics should be included in multisectoral cholera surveillance to anticipate the risk of significant geographic expansion of the disease in DRC.