Assessment of the fate of surrogates for enteric pathogens resulting from the surcharging of combined sewer systems

In the last ten years (2009-2019), flooding caused the death of over 48,000 people, and affected over 697 million people globally. This is expected to increase as a result of climate change, population growth and urbanisation. Floods can cause infections due to the release of water-borne pathogens from surcharged combined sewers and other sources of faecal contamination on urban surfaces such as concrete, asphalt, gravel, pavement, playground rubber tiles and grass. Using laboratory experiments with faecal indicator bacteria Escherichia coli, and with Bacillus subtilis spores, and MS2 bacteriophages under controlled exposure to simulated sunlight, this research contributes towards a better understanding of the environmental parameters that affect the concentration of pathogens in contaminated shallow water bodies and on different urban surfaces. Also, several sampling methods are assessed for the recovery of bacteria from flood-prone urban surfaces. This study suggests that given the sunlight conditions after an urban flood, the concentration of indicator organisms and of total suspended solids and the surface type it is possible to estimate the fate of selected pathogens. The observations and results presented in this study contribute to the development of policy-making tools for rapid implementation of appropriate measures to mitigate public health risks after flooding