A quantitative microbial risk assessment framework for cholera infection from post-flood ponds

Floods are the most common type of natural disaster worldwide and have substantial socioeconomic and environmental impacts, including public health effects. Exposure to floodwaters containing pathogens poses risks to infectious diseases such as cholera, leading to diminished well-being and even loss of life. Accra, the capital of Ghana, has a long history of flood events and cholera outbreaks. Post-flood periods have the potential for transmission of water-borne diseases with significantly higher cholera risk. This study aims to assess the health risks associated with Vibrio cholerae pathogens after flood events and evaluate their impacts on Accra's population, focusing on Alajo, a neighbourhood in Accra. A post-flood pathogen (SPATE) model was developed, integrating hydrological processes (evaporation and infiltration) and pathogen decay rate, to simulate the spatial temporal distribution of floodwater ponds and the V. cholerae concentrations therein. The infection probability was calculated with the quantitative microbial and flood risk assessment. After flooding, the risk of V. cholerae infection tends to be higher in scattered ponds near the drainage network, surrounding areas of the Onyasia river, and the urban area northeastern of Alajo. The peak risk of V. cholerae infection occurs within the first 12 h post-flooding, declining rapidly thereafter. Variations in infection probability and flood exceedance probability are observed across the area, with an overall trend of reduced infection probability with increasing return periods. Notably, children engaging in water activities face higher risks compared to adults wading in post-flood waters. These findings contribute to decision-making in flood risk management and health risk assessment, facilitating prioritization of vulnerable areas and resource allocation to mitigate and prevent the health impacts of flooding, considering explicitly for the time after flooding when the risk remains elevated.