Salmonella infections in ninety Alberta swine finishing farms: serological prevalence, correlation between culture and serology, and risk factors for infection.

The aim of this study was to determine serological prevalence for Salmonella in 90 Alberta finishing swine farms over a 5-month period; to evaluate the correlation between the detection of Salmonella by bacteriological culture and serology; and to identify risk factors for Salmonella seroprevalence. Participating farms were visited 3 times. A total of 30 blood and 15 fecal samples were collected from finishing pigs on each farm. VetScreen Salmonella covalent mix-ELISA (Svanovir) and conventional culture were performed. The apparent Salmonella seroprevalences at the sample and farm level were 13.2% (95% confidence interval [CI], 10.5-15.5%) and 83.3% (95% CI, 74-90.4%), respectively. Most of the farms had within-farm seroprevalence of <or=20%, indicating that pigs on these farms had a low exposure to Salmonella. The Salmonella farm status changed frequently across 3 visits. The correlation between fecal prevalence and seroprevalence at the farm and farm visit level was 0.71 (P < 0.0001) and 0.47 (P < 0.0001), respectively. The use of meal feed and the reported use of antimicrobials through water were associated with a lower farm seroprevalence for Salmonella. Longitudinal sampling and testing are required to properly evaluate Salmonella on-farm status. The interpretation of existing serological and culture tests for Salmonella in swine should take into consideration their imperfect sensitivity, what these tests actually measure (previous exposure vs. current shedding), and the Salmonella serovar distribution within the targeted population. Further work is necessary to demonstrate the effectiveness of on-farm interventions against Salmonella in swine.