Investigating the differences in Salmonella serovar transmission within broiler production

Almost 20% of human salmonellosis cases in the United States are linked to the consumption of undercooked, contaminated chicken. The prevalence of Salmonella in broiler breeder flocks is significantly lower than in broiler flocks, where typically 9 of 10 flocks test positive. Therefore, there is a need to understand how broiler flocks become colonized with Salmonella. This study aimed to assess the transmission of specific Salmonella serovars by profiling serovar populations at different stages of broiler production. In this study, we collected a total of 368 samples from 6 broiler complexes located across 4 states in the southeastern United States. Environmental samples were collected from breeder houses (n = 53), hatcheries (n = 45), and broiler houses immediately before chick placement (n = 44) and 7 days after placement (n = 45). These samples were analyzed to determine whether Salmonella found in broilers originates from earlier stages or from resident Salmonella persisting within the broiler house. Approximately one-quarter of pre-placement samples were Salmonella-positive, while, after 1 week, all broiler houses tested positive (Fisher's Exact test, p < 0.05). Serovar-specific transmission dynamics were observed: Serovar Enteritidis originating from broiler breeders and the hatchery colonized new chicks, while residual serovar Infantis from previous broiler flocks was responsible for colonizing the newly placed chicks. Applying deep serotyping demonstrated that 7-day-old broiler flocks harbored more complex Salmonella serovar populations than those observed at the other three stages (Fisher's, p < 0.01). Understanding the transmission differences among different serovars will facilitate the implementation of broad Salmonella control strategies and targeted interventions for specific serovars, ultimately improving poultry food safety.