Wastewater Surveillance of Salmonella enterica, Campylobacter jejuni, and Norovirus Reveals Potential Underreporting of Disease Cases in the Tri-county Detroit Area, Michigan

Abstract

Enteric pathogens Salmonella, Campylobacter, and norovirus are the leading causes of gastroenteritis in the United States. The current study applies wastewater-based epidemiology (WBE) to detect and back-estimate the prevalence of these diseases in the tri-county Detroit area (TCDA), Michigan. Concentrations of Salmonella enterica, Campylobacter jejuni, and norovirus (GI and GII) were monitored by ddPCR between January and December 2024 for norovirus and between July and December 2024 for S. enterica and C. jejuni. Average norovirus concentrations peaked during winter and spring months (1.03 × 10⁵ genome copies (gc)/L) and were higher than S. enterica (1.71 × 10⁴ gc/L) and C. jejuni (7.39 × 10² gc/L) concentrations, which peaked primarily during summer months. Based on measurements in wastewater samples, back-estimation of clinical cases revealed that these enteric pathogens are likely underreported in the TCDA when benchmarked against the clinically reported cases. This study highlights the importance of using WBE to track and estimate enteric disease cases, especially for underreported ones. Moreover, we proposed an improved back-estimation model of S. enterica and C. jejuni, incorporating an adjustment factor β to estimate the rate of bacteria’s prevalence in animals and/or animal-derived products. Furthermore, this study demonstrates disparities in the population’s incidence of these enteric pathogens.

This paper describes one of the first case estimations of norovirus, Salmonella, and Campylobacter based on wastewater surveillance. A back-estimation formula was optimized by incorporating a parameter estimating the prevalence for bacteria in animals and/or animal-derived products.