Modalities and preferred routes of geographic spread of cholera from endemic areas in eastern Democratic Republic of the Congo

Abstract

Cholera is endemic along the Great Lakes Region, in eastern Democratic Republic of the Congo (DRC). From these endemic areas, also under perpetual conflicts, outbreaks spread to other areas. However, the main routes of propagation remain unclear. This research aimed to explore the modalities and likely main routes of geographic spread of cholera from endemic areas in eastern DRC. We used historical reconstruction of major outbreak expansions of cholera since its introduction in eastern DRC, maps of distribution and spatiotemporal cluster detection analyses of cholera data from passive surveillance (2000-2017) to describe the spread dynamics of cholera from eastern DRC. Four modalities of geographic spread and their likely main routes from the source areas of epidemics to other areas were identified: in endemic eastern provinces, and in non-endemic provinces of eastern, central and western DRC. Using non-parametric statistics, we found that the higher the number of conflict events reported in eastern DRC, the greater the geographic spread of cholera across the country. The present study revealed that the dynamics of the spread of cholera follow a fairly well-defined spatial logic and can therefore be predicted.

Fig 1. Administrative map of the DRC.

Fig 2

A and B. Major outbreaks expansions of cholera documented since its introduction in eastern DRC in 1978. Sources: Fig 2A [29] and Fig 2B [30].

Fig 3. Spatiotemporal clusters of cholera cases, DRC, 2000–2005.

Arrows indicate the likely routes of spread. Dashed arrows represent two probable routes at the same period. Republished from [30] under a CC BY license, with permission from [Claire Halleux], original copyright [2021].

Fig 4. Spatiotemporal clusters of cholera cases, DRC, 2006–2011.

Arrows indicate the likely routes of spread. Dashed arrows represent two probable routes at the same period. Republished from [30] under a CC BY license, with permission from [Claire Halleux], original copyright [2021].

Fig 5. Spatiotemporal clusters of cholera cases, DRC, 2012–2017.

Arrows indicate the likely routes of spread. Dashed arrows represent two probable routes at the same period. Republished from [30] under a CC BY license, with permission from [Claire Halleux], original copyright [2021].

Fig 6. Boxplots of the weekly numbers of conflict events reported in eastern endemic provinces by geographic spread modalities of cholera outbreaks.