Surveillance of Salmonella in Cull Boar, Sow, and Gilt Lymph Nodes and Tonsils from Six Cull Hog Processing Facilities in the United States

Salmonella is associated with the environment, gastrointestinal tract, and lymph nodes (LNs) of pigs. Contamination in LNs of cull hogs may lead to contamination of carcasses, sausages, and other pork products. To better understand the public health risks of contaminated lymphatic tissues, a cross-sectional analysis of Salmonella in the LNs and tonsils of cull hogs processed at six facilities across two regions of the United States during different seasons was conducted. A total of 3,824 samples from 560 carcasses were included in this study. From each carcass, six LNs (axillary [ALN], mesenteric [MLN], subiliac [SLN], tracheobronchial [TLN], superficial inguinal [SILN], and prescapular [PLN]), and tonsils were collected. The BAX® System Real-Time Salmonella Assay and BAX®-System-SalQuant® methods were used to detect and estimate Salmonella concentration in samples, respectively. Salmonella prevalence was 12.3% overall, 36.9% in tonsils, 29.7% in MLNs, 8.2% in SILNs, 2.5% in PLNs, 4.5% in TLNs, 2.0% in ALNs, and 0.7% in SLNs. Salmonella prevalence was greatest for tonsils in the summer/fall (42.6%), though season was not significant (P = 0.1132). For MLNs, Salmonella prevalence in spring (35.2%) and summer/fall (32.5%) was significantly greater (P < 0.05) than winter (18.3%). Salmonella prevalence was significantly higher (P < 0.05) in SILNs during winter (19.2%) than spring (0.5%) and summer/fall (2.2%) in the eastern region. Of the 70 MLNs that were enumerable, estimated concentration (log Salmonella cells/sample) was greatest (P < 0.05) during winter (2.8) in comparison to summer/fall (1.8) and spring (0.7) in the eastern region. At the carcass level, 332 (59.3%) harbored Salmonella in one or more samples, and prevalence did not vary by season (P = 0.1495) or region (P = 0.8669). These data suggest that seasonal factors impact Salmonella contamination in specific lymph nodes and can be used by the industry for risk assessment and Salmonella mitigation strategies.