Penn State University researchers have demonstrated the usefulness of wastewater monitoring for foodborne pathogen surveillance, after successfully isolating Salmonella from wastewater samples and using whole genome sequencing (WGS) to link the isolates to a known salmonellosis outbreak. The findings were published in the Journal of Clinical Microbiology.

During the COVID-19 pandemic, wastewater monitoring was highly effective in identifying the variants of concern earlier than clinical surveillance methods. In this context, the Penn State team sought to explore whether the same wastewater monitoring framework could also aid traditional reporting of foodborne illnesses to public health authorities. Salmonella was chosen as the target of the study due to its prevalence as a foodborne pathogen, and also because Pennsylvanian and national infrastructures for salmonellosis reporting and genomic data collection for Salmonella already exist.

For the study, wastewater samples were collected from two central Pennsylvania treatment facilities at regular intervals during June 2022. WGS was conducted on Salmonella isolated from the samples, and the U.S. Centers for Disease Control and Prevention’s (CDC’s) Systems Enteric Disease Response, Investigation, and Coordination (SEDRIC) platform was used to verify clustering of isolates from clinical and wastewater sources. For related Pennsylvanian isolates, the researchers reviewed original records in the Pennsylvania National Electronic Disease Reporting system (PA-NEDSS). They also compared findings to summaries of outbreak investigations.

A total of 43 Salmonella isolates were recovered from wastewater samples, comprising seven serovars: 16 S. Panama isolates (37.2 percent), nine S. Seftenberg isolates (20.9 percent), eight S. Baildon isolates (18.6 percent), and three or fewer of all other serovars. Genetic similarity between the wastewater isolates and isolates from human clinical cases were assessed—all S. Baildon isolates from wastewater were found to be genetically similar to those associated with an existing foodborne illness outbreak. Of the 42 human clinical S. Baildon isolates from the existing outbreak, one was obtained from a patient who lives within the catchment area of one of the wastewater treatment plant sampling sites, which serves about 17,000 people.

As S. Baildon is a rare serovar—reported in less than one percent of salmonellosis cases nationally in a five-year period—the researchers emphasize the value of monitoring sewage from a defined population to improve foodborne illness surveillance and outbreak investigations.