Spatial patterns in surveillance data during control of Salmonella Dublin in bovine dairy herds in Jutland, Denmark 2003–2009

Salmonella Dublin is the most commonly isolated Salmonella serotype in Danish cattle and leads to economic and welfare losses in infected herds. Furthermore, it leads to high mortality in human cases. A national surveillance program for Salmonella Dublin was initiated in Denmark in October 2002. This study aimed at modelling the progress and spatial patterns during the control of Salmonella Dublin in dairy herds in the Jutland peninsula in Denmark, especially differences between regions and years. A total of 6331 dairy herds were included during 2003–2009. Antibody measurements of bulk-tank milk samples were used for testing herd-level Salmonella status in these dairy herds. Risk maps were estimated as prevalence intensity maps. Spatial clustering was analysed using scan statistics and SMR was estimated.In 2003, the prevalence of Salmonella Dublin test-positive dairy herds was 24%. It decreased to 12% in 2009. Prevalence intensity maps showed large differences in the reduction of Salmonella Dublin test-positive herds. The number of clusters reduced during the study period. However, throughout the study period two clusters remained significant. Differences were seen in the progress of the control between regions over the years. The implementation and effectiveness of the control program was different between regions. The progress of control was seen to vary not only between regions, but also over time influencing infection dynamics. Thus, recommendations and regionally targeted efforts during control campaigns are needed.

► We model spatio-temporal patterns in Salmonella Dublin surveillance data during 2003–2009.
► The prevalence of Salmonella Dublin test-positive herds decreased from 24% to 12%.
► Geographical differences were seen in the reduction of the prevalence.
► Two clusters remained significant during the study period.
► Regionally targeted efforts are needed.