Cholera epidemics, war and disasters around Goma and Lake Kivu: an eight-year survey

Abstract

Background: During the last eight years, North and South Kivu, located in a lake area in Eastern Democratic Republic of Congo, have been the site of a major volcano eruption and of numerous complex emergencies with population displacements. These conditions have been suspected to favour emergence and spread of cholera epidemics.

Methodology/principal findings: In order to assess the influence of these conditions on outbreaks, reports of cholera cases were collected weekly from each health district of North Kivu (4,667,699 inhabitants) and South Kivu (4,670,121 inhabitants) from 2000 through 2007. A geographic information system was established, and in each health district, the relationships between environmental variables and the number of cholera cases were assessed using regression techniques and time series analysis. We further checked for a link between complex emergencies and cholera outbreaks. Finally, we analysed data collected during an epidemiological survey that was implemented in Goma after Nyiragongo eruption. A total of 73,605 cases and 1,612 deaths of cholera were reported. Time series decomposition showed a greater number of cases during the rainy season in South Kivu but not in North Kivu. Spatial distribution of cholera cases exhibited a higher number of cases in health districts bordering lakes (Odds Ratio 7.0, Confidence Interval range 3.8-12.9). Four epidemic reactivations were observed in the 12-week periods following war events, but simulations indicate that the number of reactivations was not larger than that expected during any random selection of period with no war. Nyiragongo volcanic eruption was followed by a marked decrease of cholera incidence.

Conclusion/significance: Our study points out the crucial role of some towns located in lakeside areas in the persistence of cholera in Kivu. Even if complex emergencies were not systematically followed by cholera epidemics, some of them enabled cholera spreading.

Figure 1. Time-series of the number of weekly cholera cases from 2000 to 2007.

A: North Kivu and B: South Kivu; yellow: dry season, blue: rainy season. Time-series (data, weekly number of cases) are broken down into seasonal, trend and remainder components. Seasonal, trend and remainders sum to the weekly number of cases (data).

Figure 2. Distribution of cholera in North and South Kivu from 2000 through 2007.

Average annual attack rate of cholera per 10,000 inhabitants, in each health district.

Figure 3. Cholera outbreaks and main events in the 5 synchronous sets (Z) of health districts.

War events (W) and the main natural disaster (Nyiragongo eruption- E) observed in North and south Kivu from 2000 to 2007. Zone 1: Mutwanga; Zone 2: Goma, Rutshuru, Kirotshe; Zone 3: Bukavu, Katana. Zone 4: Uvira, Nundu, Fizi; Zone 5: Pinga, Walikale. The vertical axis represents the remainders of the time-series (this removes the undesirable effects of seasonal and inter-annual trends; in red: the periods above average; in green: those below average). War events, which occurred during an already occurring outbreak, are circled in black. War events followed by cholera outbreak starting within 12 weeks are circled in red.