Sachet water consumption as a risk factor for cholera in urban settings: findings and implications from a case control study in Kinshasa, Democratic Republic of the Congo during the 2017-2018 outbreak

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Abstract Background: Cholera is endemic in the Democratic Republic of the Congo. Starting in 2016, a cholera epidemic swept through the country and in November 2017 reached the capital of Kinshasa, which had not experienced a cholera outbreak for nearly a decade. Behavioural risk factors for cholera are well established in rural and semi-urban contexts but not in densely populated mega-cities from Sub-Saharan Africa. Such information is crucial to guide context-specific control measures. We seized the outbreak in Kinshasa as an opportunity to investigate context-specific risk factors for cholera in this urban setting among a mobile population that is not frequently exposed to cholera. Methods: We recruited 390 participants into a 1:1 age-matched case control study from three affected health zones of Kinshasa between 1 and 28 February 2018. Cases were identified from cholera treatment centre admission records, while controls were recruited from the neighbourhood of the cases’ place of residence. We collected data on socio-demographic and behavioural risk factors using standardized case report forms. We used augmented backward elimination in a conditional logistic regression model to identify risk factors, using a p-values of 0.05 as cut-off to define statistical significance. Results: The consumption of sachet water was significantly associated with the risk of being a cholera case (p-value 0.019), which increased with increasing frequency of consumption from rarely [OR 2.223, 95% CI 0.944-5.235] to often [OR 4.031, 95% CI 1.642-9.891] to very often [OR 4.144, 95% CI 1.029-16.653]. Overall, more than 80% of all participants reported consumption of this type of drinking water. Funeral attendance and recent contact with someone suffering from diarrhoea were borderline insignificant risk factors (p-value 0.09 and 0.08, respectively). No socio-demographic characteristics were associated with the risk of cholera. Conclusions: Drinking water consumption from sachets, which are sold informally on the streets in most Sub-Saharan African cities, should be considered as a potential route of infection during future cholera outbreaks in similar urban settings. Outbreak investigation and response need to acknowledge context-specific risk factors to remain a valuable tool in the efforts to achieve national and regional targets to reduce the burden of cholera in Africa.

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