First introduced in the 1940s as a means to track polio outbreaks, wastewater surveillance has proven to be a highly effective method for disease monitoring. As a result, the U.S. Centers for Disease Control and Prevention (CDC) launched the National Wastewater Surveillance System in September 2020 to assist in monitoring SARS-CoV-2. Recently, researchers from Penn State and the Pennsylvania Department of Health have demonstrated that monitoring domestic sewage can also be beneficial for tracking a foodborne pathogen.
Originally used in the 1940s to keep an eye on polio, wastewater surveillance has emerged as an effective tool for monitoring diseases. This led the U.S. Centers for Disease Control and Prevention (CDC) to set up the National Wastewater Surveillance System in September 2020 to aid in observing SARS-CoV-2. Now, a research team from Penn State and the Pennsylvania Department of Health has revealed that monitoring household sewage can help identify foodborne pathogens as well.
In a study released today (Sept. 19) in the Journal of Clinical Microbiology, researchers found evidence of Salmonella enterica bacteria in samples taken from two wastewater treatment facilities in central Pennsylvania during June 2022.
“Non-typhoidal Salmonella significantly contributes to gastroenteritis cases around the globe, but existing monitoring for this disease is insufficient,” shared Nkuchia M’ikanatha, the lead epidemiologist at the Pennsylvania Department of Health and an associate researcher in Penn State’s Department of Food Science within the College of Agricultural Sciences. “Through this research, we aimed to assess the effectiveness of wastewater monitoring in enhancing surveillance for this foodborne pathogen. Testing wastewater can reveal the presence of infectious diseases in a community, even among individuals showing no symptoms, providing an early warning for possible outbreaks.”
Although health professionals are obligated to report cases of salmonellosis, many instances remain unreported. Salmonella bacteria, found in the intestines of both humans and animals, are excreted in feces. According to the CDC, Salmonella causes approximately 1.35 million infections, 26,500 hospitalizations and about 420 deaths each year in the U.S., predominantly through the consumption of contaminated food.
In June 2022, the researchers collected raw sewage samples bi-weekly from two treatment facilities in central Pennsylvania to test for non-typhoidal Salmonella and used whole genome sequencing to analyze the isolates. They identified 43 Salmonella isolates from wastewater samples, dividing them into seven serovars based on genomic analysis. Notably, eight of these isolates, or almost 20%, belonged to a rare serovar known as Baildon.
The researchers compared the genetic relationships and epidemiological connections between non-typhoidal Salmonella isolates discovered in wastewater and similar bacteria from patients diagnosed with salmonellosis. The Salmonella Baildon serovars found in wastewater were genetically identical to those linked to a salmonellosis outbreak in the same area during that time. This included a related isolate obtained from a patient who lived in the vicinity of the wastewater sample collection area, serving approximately 17,000 residents.
Salmonella Baildon is infrequently reported, occurring in less than 1% of cases nationally over a five-year period, according to M’ikanatha, the study’s lead author. He highlighted how this research underscores the importance of monitoring domestic sewage from defined populations to complement traditional surveillance methods for detecting Salmonella infections and to assess the reach of outbreaks.
“Utilizing whole genome sequencing, we demonstrated that Salmonella Baildon isolates from wastewater clustered with those from a concurrent outbreak,” he explained. “Most case reports came from Pennsylvania, and one individual was from within the catchment area of the treatment plant. This study strengthens the case for employing domestic sewage monitoring as a tool for public health agencies to identify communities affected by infectious diseases.”
Ed Dudley, a food science professor and the study’s senior author, pointed out that these results emphasize the potential of wastewater monitoring as an early alert system for foodborne disease outbreaks, possibly even before healthcare providers and laboratories report them. This proactive method could help health officials effectively trace the source of contaminated food, thereby minimizing the number of affected individuals, according to Dudley, who also leads Penn State’s E. coli Reference Center.
“While it may take time, I envision a future where many, if not a majority, of domestic wastewater treatment plants will provide untreated sewage samples for monitoring various health issues,” he said. “This would likely involve collaboration between public health organizations, academic institutions, and federal agencies, similar to our pilot study. I see this as another vital lesson learned from the pandemic.”
Contributing to this research at Penn State were Jasna Kovac, an associate professor of food science, and Lester Earl and Veronica Casida Career Development Professor of Food Safety; Erin Nawrocki and Yezhi Fu, postdoctoral fellows in the Dudley Lab; Zoe Goldblum, an undergraduate researcher in the Department of Food Science; and Nicholas Cesari from the Division of Infectious Disease Epidemiology at the Pennsylvania Department of Health.
This study was funded by the CDC, the U.S. Food and Drug Administration, and the National Institute of Food and Agriculture of the U.S. Department of Agriculture.