Association of pBI143 with Gastrointestinal Pathogens and Threshold-Based Prediction of Salmonella spp. Outbreaks

Abstract

Wastewater-based epidemiology (WBE) offers population-level insights into enteric pathogen circulation and potential outbreak activity. We conducted a year-long (2024) surveillance across two wastewater treatment plants in Baltimore, MD (50 influent samples), quantifying adenovirus, enteropathogenic E. Coli (EPEC), and Salmonella spp. by qPCR alongside fecal markers (crAssphage and pBI143). Seasonal outbreak thresholds for Salmonella were defined using the WHO 95th-percentile approach within each season, and wastewater signals were compared with CDC-reported Salmonella outbreaks and FDA product recalls. Adenovirus and E. coli were detected in 100% of samples whereas Salmonella was detected in 84% of samples and showed pronounced seasonality, peaking in summer and fall. Pathogen-marker associations were stronger for adenovirus (crAssphage r = 0.73; pBI143 r = 0.69) and E. coli EPEC (crAssphage r = 0.66; pBI143 r = 0.61) than for Salmonella (overall r = 0.49 with crAssphage; r = 0.39 with pBI143), excluding winter increased Salmonella-marker correlations to 0.56 for crAssphage and 0.58 for pBI143. Seasonal outbreak thresholds for Salmonella were defined using the WHO 95th-percentile approach within each season. Eight weeks exceeded seasonal Salmonella thresholds (four at each plant); 50% occurred within or 2-4 weeks before a CDC-confirmed outbreak, and an additional 25% aligned with FDA recall-linked events, yielding 75% concordance of exceedances with documented outbreak/recall activity. Wastewater Salmonella concentrations correlated with reported cases (p < 0.05). These findings show the utility of the novel plasmid pBI143 for tracking enteric pathogens and demonstrate that threshold-based Salmonella alerts provide timely, additional information for outbreak detection, complementing case-based surveillance in urban communities.