Wastewater monitoring can detect foodborne illness, researchers find

Wastewater surveillance was first used in the 1940s to monitor polio and proved to be such a powerful disease monitoring tool that the U.S. Centers for Disease Control and Prevention (CDC) established the National Wastewater Surveillance System in September 2020 to support SARS-CoV-2 monitoring. Now, a team of scientists from Penn State and the Pennsylvania Department of Health has shown that monitoring household sewage is also useful for a foodborne pathogen.

With findings published September 19 in the Journal of Clinical Microbiologyresearchers report that the bacteria Salmonella enterica was detected in samples from two wastewater treatment plants in central Pennsylvania in June 2022.

“Nontyphoidal Salmonella is a common cause of gastroenteritis worldwide, but current surveillance of the disease is suboptimal. Therefore, in this study we evaluated the utility of wastewater monitoring to improve surveillance of this foodborne pathogen,” says Nkuchia M’ikanatha, chief epidemiologist. , Pennsylvania Department of Health and an affiliated researcher in Penn State’s Department of Food Science in the College of Agricultural Sciences.

“In this study, we examined wastewater monitoring as a tool to improve surveillance of this foodborne pathogen. Wastewater testing can detect traces of infectious diseases circulating in a community, even in asymptomatic individuals, and provide an early warning system for possible outbreaks.”

Although healthcare providers are required to report cases of salmonellosis, many cases go undetected. Salmonella bacteria, which live in the intestines of animals and humans, are excreted through the feces. The CDC estimates that Salmonella causes approximately 1.35 million infections, 26,500 hospitalizations and 420 deaths annually in the U.S., mostly from contaminated food.

In June 2022, the researchers tested raw sewage samples collected twice a week from two treatment plants in central Pennsylvania for non-typhoidal Salmonella and characterized isolates using whole genome sequencing. They recovered 43 Salmonella isolates from wastewater samples, which were distinguished by genomic analysis into seven serovars, which are groups of microorganisms based on similarities. Eight of the isolates, or almost 20%, were from a rare form of Salmonella called Baildon.

The researchers assessed the genetic relatedness and epidemiological links between non-typhoidal Salmonella isolates from wastewater and similar bacteria from patients with salmonellosis. The Salmonella Baildon serovars isolated from wastewater were genetically indistinguishable from a similar bacterium found in a patient associated with a salmonellosis outbreak in the area during the same period.

Salmonella Baildon from wastewater and 42 outbreak-related isolates in the National Outbreak Detection Database had the same genetic makeup. One of the 42 isolates associated with the outbreak was obtained from a patient residing in the wastewater research sample collection basin, which serves approximately 17,000 people.

Salmonella Baildon is a rare serovar – reported in less than 1% of cases nationwide over five years, noted M’ikanatha, the study’s first author. He pointed out that this study demonstrates the value of monitoring sewage from a defined population to supplement traditional surveillance methods for evidence of Salmonella infections and to determine the extent of outbreaks.

“Using whole genome sequencing, we showed that isolates of the Salmonella Baildon variant clustered with those from an outbreak that occurred in a similar time frame,” he said.

“Case reports were primarily from Pennsylvania, and one individual lived in the treatment plant watershed. This study provides support for the use of domestic sewer surveillance in helping public health agencies identify communities affected by infectious diseases.”

Ed Dudley, professor of food sciences and lead author of the study, said these findings highlight the potential of wastewater monitoring as an early warning system for foodborne illness outbreaks, potentially even before doctors and laboratories report cases. This proactive approach could allow health officials to quickly track down the source of contaminated food, ultimately reducing the number of people affected, suggested Dudley, who also directs Penn State’s E. coli Reference Center.

“While this may not happen overnight, I foresee a future where many, if not most, domestic wastewater treatment plants provide untreated sewage samples for monitoring evidence of various diseases,” he said. “This would likely involve collaboration between public health agencies, academia, and federal entities, much like our pilot study. I see this as yet another crucial lesson from the pandemic.”