Epidemic cholera in Burundi: patterns of transmission in the Great Rift Valley Lake region

Abstract

Background: After a 14-year hiatus, epidemic cholera swept through Burundi between January and May, 1992. The pattern of transmission was similar to that in 1978, when the seventh pandemic first reached this region. Communities affected were limited to those near Lake Tanganyika and the Rusizi River. The river connects Lake Tanganyika with Lake Kivu to the north in Zaire and Rwanda.

Methods: To identify sources of infection and risk factors for illness, an epidemiological study was carried out in Rumonge, a lake-shore town where 318 people were admitted to hospital with cholera between April 9 and May 31, 1992. The investigation included a case-control study of 56 case-patients and 112 matched controls.

Findings: Attack rates according to street increased with the street's proximity to Lake Tanganyika (chi 2 test for linear trend, p < 0.01) which suggests that exposure to the lake was a risk factor for illness. Comparison of the 56 case-patients with matched controls showed that bathing in the lake (odds ratio 1.6, attributable risk percentage 37%) and drinking its water (2.78, 14%) were independently and significantly (p < 0.05) linked with illness. No food-borne risk factors were identified. Vibrio cholera 01 was isolated from Lake Tanganyika during, but not after, the outbreak in Rumonge. Isolates from the lake and from patients with acute watery diarrhoea had the same serotype, biotype, and antimicrobial susceptibility profiles. The number of cases rapidly declined when access to the lake was blocked.

Interpretation: This study identifies bathing in contaminated surface water as a major risk factor for cholera in sub-Saharan Africa, and suggests that improving the quality of drinking water alone will have only limited impact on the transmission of the disease in the Great Rift Valley Lake region. The similarity in the patterns of transmission during the 1978 and 1992 epidemics suggests that extensive use of the Great Lakes and connecting rivers for transportation and domestic purposes may be the reason for the explosive cholera outbreaks that occur sporadically in this region.