A Salmonella serovar was identified in Pennsylvania wastewater, which accounts for less than 1% of U.S. cases over 5 years and found to be genetically linked to a concurrent outbreak, suggesting that sewage monitoring could support traditional surveillance efforts, according to a recent study.
In the study, published in Clinical Microbiology, researchers collected raw sewage samples twice weekly from two wastewater treatment plants in central Pennsylvania in June 2022, identifying 43 isolates of Salmonella. Whole-genome sequencing revealed seven serovars, including Panama (37.2%), Senftenberg (20.9%), and Baildon (18.6%). The S. Baildon isolates identified in wastewater exhibited genetic similarities to those linked with a salmonellosis outbreak occurring at the same time.
Genomic analysis demonstrated that the S. Baildon isolates from wastewater and clinical sources had highly similar core genome multilocus sequence typing profiles, differing by zero or one single nucleotide polymorphism. This finding aligns with the outbreak, which was linked to consumption of contaminated tomatoes and lettuce. One outbreak-related clinical case was identified within the wastewater catchment area, which serves a population of approximately 17,000.
The findings demonstrated the utility of wastewater monitoring as a supplementary tool to traditional surveillance for non-typhoidal Salmonella, a common etiologic agent of gastroenteritis.
The wastewater treatment plants in Pennsylvania were chosen for their convenience to the laboratory, potentially limiting regional representativeness. Additionally, the sampling period was less than 1 month (June 2022), which may not capture the full variability of Salmonella isolation rates over time.
The researchers suggested that sewage surveillance may serve as an additional tool for public health monitoring, aiding in identifying outbreaks and tracking the spread of foodborne illnesses. Wastewater-based epidemiology, as applied during the COVID-19 pandemic, provided insights into community transmission, and a similar approach may be implemented for tracking Salmonella infections. Considering that traditional Salmonella surveillance identified only 52,575 of an estimated 1.03 million U.S. cases in 2023, sewage monitoring suggests the potential to aid in early detection and case identification efforts.
Full disclosures can be found in the published study.