Pathways of Exposure toVibrio Choleraein an Urban Informal Settlement in Nairobi, Kenya

Cholera is a diarrhoeal disease caused by the toxigenic Vibrio cholerae ( V. cholerae ) bacterium. V. cholerae can contaminate drinking water sources and food through poor sanitation and hygiene, especially in informal settlements and refugee camps where cholera outbreaks have been reported in Kenya. This study aimed to identify environmental transmission routes of V. cholerae within Mukuru informal settlement in Nairobi. We collected nine types of environmental samples (drinking water, flood water, open drains, surface water, shaved ice, raw produce, street food, soil, and public latrine swabs) over 12 months. All samples were analysed for V. cholerae by culture and qPCR, then qPCR-positive samples were quantified using a V. cholerae DNA standard. Behavioural data was collected to determine the frequency of contact with the environment among adults and children. Of the 803 samples collected, 20.4% were positive for V. cholerae by qPCR. However, none were positive for V. cholerae by culture. V. cholerae genes were detected in the majority of the environmental water samples (79.3%), including open drains, flood water, and surface water, but were only detected in small proportions of other sample types. Vibrio-positive environmental water samples had higher mean V. cholerae concentrations [2490–3469 genome copies (gc) per millilitre (mL)] compared to drinking water samples (25.6 gc/mL). Combined with the behavioural data, exposure assessment showed that contact with surface water had the highest contribution to the total V. cholerae exposure among children while ingestion of municipal drinking water and street food and contact with surface water made substantial contributions to the total V. cholerae exposure for adults. Detection of V. cholerae in street food and drinking water indicates risk of both endemic and epidemic cholera. Exposure to V. cholerae through multiple pathways highlights the need to improve water and sanitation infrastructure, strengthen food hygiene practices, and roll out cholera vaccination.