Prevalence of Salmonella Dublin in dairy herds in Alberta, Canada

Salmonella enterica subspecies enterica serotype Dublin (Salmonella Dublin) is a zoonotic pathogen host adapted to cattle. The objective of this study was to provide updated herd-level prevalence estimate of Salmonella Dublin in Alberta dairy herds. A 40 mL bulk tank milk sample was collected from all active dairy herds (n=468) in Alberta in June 2024 and tested for Salmonella Dublin antibodies using indirect ELISA. Two different percent positive (PP%) cut-off values were used (≥ 35 and ≥ 15) to classify samples into positive and negative. Apparent prevalence was calculated as proportion of positive herds out of total herds and a true prevalence was estimated using Rogan-Gladen method for both cut-off values separately. Using PP% ≥ 35 cut-off, apparent prevalence and true prevalence were estimated to be 10.3%, and 56.2%, respectively, with a positive and negative predictive value of 0.54 and 0.86 , respectively. Using PP% ≥ 15 apparent and true prevalence were 20.5% and 38.2%, respectively, with a positive and negative predictive value of 0.67 and 0.79, respectively. Medium and large herds had higher odds (odds ratio (OR) = 4.55; p-value = 0.03, and OR = 4.48; p-value 0.04, respectively) of testing positive using PP% ≥ 35 cut-off than small herds in central region. The small herds in south region were more frequent (OR = 4.96; p-value 0.02) positive than central region. These results provide latest updates on prevalence of herds positive for antibodies against Salmonella Dublin in Alberta and contribute to the ongoing surveillance efforts.