Evaluation of sampling and concentration methods for Salmonella enterica serovar Typhi detection from wastewater

Salmonella enterica serovar (Salmonella Typhi) is the causative bacterial agent of Typhoid fever. Environmental surveillance of wastewater and wastewater-impacted surface waters has proven effective in monitoring various pathogens, and has recently been applied to Salmonella Typhi. This study evaluated eight sample collection and concentration methods with twelve variations currently being developed and used for Salmonella Typhi surveillance globally to better understand the performance of each method based on their ability to detect Salmonella Typhi and feasibility. Salmonella Typhi strains, Ty21a and Ty2, were seeded to influent wastewater at known concentrations to evaluate the following methods: grab sampling using electropositive filters, centrifugation, direct enrichment, or membrane filtration and trap sampling using Moore swabs. Concentrated samples underwent nucleic acid extraction and were detected and/or quantified via qPCR. Results suggest that all methods tested can be successful at concentrating Salmonella Typhi for subsequent detection by qPCR, although each method has its own strengths and weaknesses including the Salmonella Typhi concentrations they are best suited for with a range of positive detections observed as low as 0.1-0.001 CFU Ty21a/mL and 0.01 CFU Ty2/mL. These factors should be considered when identifying a method for environmental surveillance and will greatly depend on the use case planned.