Determining the prevalence of antibodies to Salmonella Dublin in dairy herds in Great Britain by quarterly bulk tank testing

Salmonella enterica subspecies enterica serovar Dublin has been the most common Salmonella serovar isolated from cattle in Great Britain for the previous 22 years. It can cause a wide variety of clinical presentations and result in significant welfare and productivity concerns in infected herds. Bulk tank antibody testing undertaken every three or four months forms the basis of eradication and monitoring programmes in Denmark and the Netherlands and has been shown to be a sensitive, specific and cost-effective way of establishing seroprevalence and monitoring infection at a herd level. A prevalence estimate based on quarterly bulk tank testing has not been previously carried out in Great Britain. This study recruited 410 herds across Great Britain, who submitted milk samples on a quarterly basis for screening by an ELISA for Salmonella Dublin antibody. Classifying herds according to the Danish eradication scheme classification gave an apparent prevalence of 38% (95% confidence intervals 34-43%) and an estimated true prevalence of 40% (95% confidence intervals 35-45%), taking into account the test sensitivity and specificity. Of the 401 herds which completed the quarterly bulk tank testing, 45% had one or more positive bulk tank results.