Outbreak-associated Salmonella Baildon found in wastewater demonstrates how sewage monitoring can supplement traditional disease surveillance

Non-typhoidal Salmonella is a common cause of gastroenteritis worldwide, but current non-typhoidal Salmonella surveillance is suboptimal. Here we evaluated the utility of wastewater monitoring to enhance surveillance for this foodborne pathogen. In June 2022, we tested composite raw sewage collected twice a week from two treatment plants in central Pennsylvania for non-typhoidal Salmonella and characterized isolates using whole genome sequencing. We recovered 43 Salmonella isolates from wastewater samples, differentiated by genomic analysis into seven serovars: 16 Panama (37.2%), 9 Senftenberg (20.9%), and 8 Baildon (18.6%), 3 or fewer for four other serovars. We assessed genetic relatedness and epidemiologic links between non-typhoidal Salmonella serovars from wastewater and isolates from patients with salmonellosis. All S. Baildon serovars from wastewater were genetically and epidemiologically associated with a known salmonellosis outbreak. S. Baildon from wastewater and 42 outbreak-related isolates in the national outbreak detection database had the same core genome multilocus sequence typing and code differed by no or one single polynucleotide polymorphisms. One of the 42 outbreak-related isolates was obtained from a patient residing in the wastewater sample collection catchment area, which serves approximately 17000 people. S. Baildon is a rare serovar (reported in <1% cases nationally over five years). Our study underscores 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. Importance statementDuring the COVID-19 pandemic, surveillance for SARS-CoV-2 in wastewater was a powerful tool for assessing community burden days ahead of traditional reporting. Here, we show that domestic sewage monitoring is useful for surveillance for a foodborne pathogen. Salmonella enterica was detected in samples from two wastewater treatment plants in central Pennsylvania during June 2022. Using whole genome sequencing, we demonstrated that isolates of variant S. Baildon clustered with those from an outbreak that occurred in a similar time frame. Case reports were primarily from Pennsylvania, and one individual lived within the treatment center catchment area. This study provides support for the utility of domestic sewage surveillance in assisting public health agencies identify communities impacted by infectious diseases.