Wastewater surveillance has been used since the 1940s to monitor disease outbreaks, starting with polio. The U.S. Centers for Disease Control and Prevention established the National Wastewater Surveillance System in 2020 to monitor SARS-CoV-2. A new study by scientists from Penn State and the Pennsylvania Department of Health shows that wastewater monitoring can also be effective for detecting foodborne pathogens like Salmonella enterica, which causes gastroenteritis. This research aimed to enhance surveillance for this pathogen, as current methods are suboptimal. Wastewater testing can detect infectious diseases in a community, even in asymptomatic individuals, providing an early warning system for potential outbreaks.
Salmonella bacteria are commonly found in the intestines of animals and humans, and are shed in feces. The CDC estimates that Salmonella causes over 1.35 million infections, 26,500 hospitalizations, and 420 deaths annually in the U.S. The researchers collected raw sewage samples twice a week from two treatment plants in central Pennsylvania in June 2022 and tested them for non-typhoidal Salmonella. They recovered 43 Salmonella isolates, with eight of them belonging to a rare type called Baildon. Genetic analysis showed that Salmonella Baildon isolates from wastewater were genetically similar to bacteria found in patients with salmonellosis, indicating a connection between the two.
The study assessed genetic relatedness and epidemiologic links between Salmonella isolates from wastewater and patients with salmonellosis. The genetic makeup of Salmonella Baildon from wastewater samples matched outbreak-related isolates in a national database. One patient in the outbreak lived in the wastewater study sample collection catchment area, serving approximately 17,000 people. This research demonstrates the value of monitoring sewage from a defined population to supplement traditional surveillance methods for Salmonella infections, providing evidence of outbreaks and aiding in outbreak investigation.
The researchers used whole genome sequencing to show that Salmonella Baildon isolates from wastewater clustered with those from an outbreak in a similar time frame. Case reports were primarily from Pennsylvania, with one individual living in the treatment plant catchment area. This study supports the use of domestic sewage surveillance to help public health agencies identify communities affected by infectious diseases. Wastewater monitoring has the potential to serve as an early warning system for foodborne disease outbreaks, enabling health officials to trace the source of contaminated food and reduce the number of people affected. The proactive approach can provide valuable insights into outbreak detection and prevention.
Ed Dudley, a professor of food science at Penn State, highlighted the potential of wastewater monitoring in detecting foodborne disease outbreaks before they are reported by physicians and laboratories. He envisions a future where many domestic wastewater treatment plants contribute samples for monitoring evidence of various illnesses, leading to collaboration among public health agencies, academia, and federal entities. This collaborative effort, similar to the pilot study conducted by the researchers, could offer important lessons from the pandemic and contribute to improved disease surveillance strategies. The study was supported by funding from the CDC, the U.S. Food and Drug Administration, and the U.S. Department of Agriculture’s National Institute of Food and Agriculture.