Prevalence and risk factors for Salmonella infection in layer flocks in Israel between 2018 and 2023

Non-typhoidal Salmonella infections are a leading food-borne zoonosis in which poultry and egg products play an important epidemiological role. Identification of risk factors for Salmonella infections is crucial for reducing Salmonella prevalence and protecting public health. Although Salmonella prevalence in layers is actively monitored, analysis of potential risk factors, particularly those related to proximity to other livestock farms, has not been conducted previously. This study aimed to estimate the prevalence and identify risk factors, especially proximity to dairy farms, for Salmonella and its predominant serovars infections in layer flocks in Israel between 2018 and 2023. Overall, 24,500 sampling events from a census of 6,076 laying hen flocks, which were collected as part of the national active Salmonella surveillance program, were included in the cross-sectional analysis. We estimated overall Salmonella prevalence, the prevalence of serovars S. Enteritidis (SE) and S. Typhimurium (ST), and the association between multiple risk factors and infection. Univariable and multivariable mixed-effects regression models were applied, with nested random effects to account for shared locality, farm ownership, and repeated measures. The overall prevalence of positive Salmonella sampling events was 17.74 % (4,347/24,500), and the cumulative flock-level prevalence was 42.56 % (2,586/6,076). SE and ST were detected in 2.98 % (181/6,076) and 2.09 % (127/6,076) of flocks, respectively. Older bird age (>85 weeks), larger flock size (>10,000 hens), caged housing system, and sampling during fall were significantly associated with increased Salmonella detection in the multivariable models (p < 0.05). SE and ST detection was associated with older bird age (>85 weeks) and sampling by the Israeli Veterinary Services vs. Egg and Poultry Board inspectors. These findings emphasize the role of flock management and environmental context in Salmonella complex epidemiology in layer flocks. While the distance to dairy farms may not affect the risk of infection, maintaining smaller flocks (under 10,000 hens) in non-caged systems for shorter production cycles could help lower the prevalence of Salmonella in laying hens.