Salmonella in broiler breeder flocks in Israel during 2008-2018: Prevalence, risk factors and repeated detections

Non-typhoidal Salmonella infections in broiler breeder flocks pose a major economic challenge to poultry production and increased risk to public health. This study aimed to determine the prevalence and risk factors for infections in commercial broiler breeder flocks in Israel, and the risk for repeated detections. Data comprised a census of 4,100 flocks from 142 farms, with 64,217 test results derived from national surveillance program records collected during 2008-2018. Prevalence was calculated at the test, flock, and farm level. Univariable and multivariable mixed-effect logistic regression models were used to assess risk factors for detection at the test level, accounting for clustering within flocks and farms. Repeated detections were analyzed separately at the flock and farm levels using descriptive statistics, and logistic regression models. In addition, the prevalence and incidence of dominant serotypes infecting broiler breeder flocks and humans, respectively, were compared. On average, 6.7% of tests were Salmonella-positive annually, and 29.6% of flocks and 59.6% of farms tested positive at least once per year. Overall, 91 serotypes were identified, with five dominant serotypes (Infantis, Hadar, Kentucky, Muenchen and Virchow) accounting for 67% of isolates. The risk for Salmonella detection was higher in the fall season, in younger flocks (≤45 weeks), when sampled by the Israeli Veterinary Services, in the Center region (vs. South), and in the Ross breed. Repeated detections (at least two positive detections) were found in ∼70% of the positive flocks, with an average of 13% of subsequent tests positive after initial detection; older age at first detection (>45 weeks), and Ross breed (vs. other) increased odds of repeated detection. Comparison of serotypes between broiler breeder flocks and humans revealed substantial overlap in dominant serotypes, yet not with serotypes Enteritidis and Typhimurium. Overall, our findings highlight the complex epidemiology of salmonellosis in broiler breeder flocks. The high prevalence and persistence of Salmonella in these flocks, despite continuous control efforts, emphasize the remaining gaps in knowledge for mitigating this important pathogen and protecting the food chain.