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Background Behavioural risk factors for cholera are well established in rural and semi-urban contexts, but not in densely populated mega-cities in Sub-Saharan Africa. In November 2017, a cholera epidemic occurred in Kinshasa, the Democratic Republic of the Congo, where no outbreak had been recorded for nearly a decade. During this outbreak, we investigated context-specific risk factors for cholera in an urban setting among a population that is not frequently exposed to cholera. Methodology/Principal findings We recruited 390 participants from three affected health zones of Kinshasa into a 1:1 matched case control study. Cases were identified from cholera treatment centre admission records, while controls were recruited from the vicinity of the cases’ place of residence. We used standardized case report forms for the collection of socio-demographic and behavioural risk factors. We used augmented backward elimination in a conditional logistic regression model to identify risk factors. The consumption of sachet water was strongly associated with the risk of being a cholera case (p-value 0.019), which increased with increasing frequency of consumption from rarely (OR 2.2, 95% CI 0.9–5.2) to often (OR 4.0, 95% CI 1.6–9.9) to very often (OR 4.1, 95% CI 1.0–16.7). Overall, more than 80% of all participants reported consumption of this type of drinking water. The risk factors funeral attendance and contact with someone suffering from diarrhoea showed a p-value of 0.09 and 0.08, respectively. No socio-demographic characteristics were associated with the risk of cholera. Conclusions/Significance Drinking water consumption from sachets, which are sold informally on the streets in most Sub-Saharan African cities, are an overlooked route of infection in urban cholera outbreaks. Outbreak response measures 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 Sub-Saharan Africa., Author summary Cholera is a diarrheal disease caused by ingestion of the Vibrio cholerae bacterium. Outbreaks in urban areas are becoming increasingly frequent in Sub-Saharan Africa. Risk factors for cholera have been studied in rural settings but not sufficiently in urban areas. Understanding context-specific risk factors is key for successful outbreak response. During a cholera outbreak in Kinshasa, the Democratic Republic of the Congo we were able to identify a previously unknown behavioural risk factor of particular relevance in urban settings–the consumption of drinking water from plastic sachets. Water sachets are sold on the streets of all major cities in Sub-Saharan Africa. It requires biting off an edge and sucking out the water, and we think that external contamination of these sachets was an important transmission route in the Kinshasa outbreak. Water sachets are predominantly consumed by socio-economically disadvantaged groups who lack piped water supply in their homes and have poor access to sanitary infrastructure. This makes our findings particularly relevant because these are the very populations who are at increased risk of getting and transmitting cholera. Health messaging and response measures should include consumption of water sachets as a potential risk factor during future cholera outbreaks in urban low-resource settings.

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.