A comparative quantitative microbial risk assessment of fecal sludge management systems: A case study of Mukuru Kwa Njenga Slum in Kenya

ABSTRACT Pictorial presentation of the research paper. Safely managed sanitation systems should protect humans from fecal contamination through every possible exposure pathway. However, different fecal sludge management (FSM) systems pose varying health risks along the service chain. This study applied quantitative microbial risk assessment to estimate health risks posed by eight FSM systems in Kenya's Mukuru Kwa Njenga Slum. Based on four reference pathogens: Vibrio cholerae, Rotavirus, Cryptosporidium spp., and Ascaris lumbricoides, the study considered maximally exposed users, workers, and residents, through ingestion from hands, water, soil, and vegetables. It aimed at aiding targeted mitigation measures. Open defecation posed the highest estimated daily probability of infection (93%), followed by manual pit emptying at 88%. The closed waterless pit system posed the lowest average risk of infection at 10% compared with the manually emptied systems and the water-based systems. This was due to increased exposure pathways and subsequent downstream contamination, respectively. V. cholerae was the most prevalent pathogen, posing an estimated disease burden of 4.27 × 10−1 disability adjusted life years per person per year, due to high case fatality rates. Therefore, health risk mitigation strategies such as effective use of personal protective equipment should target specific exposed population including cleaners, pit emptiers, and treatment workers.