Describing the Salmonella classification levels for low-volume production systems utilizing abattoir-based samples and classification stability over time
James D. McKean, DVM, MS, JD; Annette M. O’Connor BVSc, MVSc, DVSc
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Objective: To compare estimates of the prevalence of meat-juice-based antibodies to Salmonella in swine originating from low-volume production systems (marketing ≤ 8000 pigs per year) during 2002 and 2004.
Materials and methods: Results of testing meat-juice samples by a commercial indirect enzyme-linked immunosorbent assay (ELISA) were available for 2002 and 2004 for swine marketed by 502 low-volume swine-production systems through eight commercial Iowa abattoirs with high throughput (> 1000 head per hour).
Results: In 2002, 934 of 14,401 samples (6.5%), and in 2004, 1639 of 13,718 samples (11.9%) were seropositive for Salmonella (ELISA sample-to-positive ratio ≥ 0.4). Average Salmonella seroprevalence in 2002 was 6.8%, median prevalence was 0.8%, and within-producer prevalence range was 0% to 59.2%. In 2004, average seroprevalence was 11.8%, median prevalence was 5.2%, and range was 0% to 81.8%. In 47% of low-volume production systems classified according to the Danish Salmonella classification system, classification did not change from 2002 to 2004. However, 53% of systems did change classification, with most moving to classifications representing higher observed seroprevalence.
Implications: Population Salmonella seroprevalence is not stable within defined and matched swine-production cohorts over time. Within-herd Salmonella seroprevalence is not stable in smaller production herds over time. These variations should be considered when making inferences about the risk of Salmonella in individual sites or swine-producing regions and for intervention programs that measure success by monitoring Salmonella seroprevalence at the production-system level. Classification of production-system status based on Salmonella antibody prevalence is an unstable outcome over time.
Keywords: Salmonella, zoonosis, Salmonella seroprevalence, meat-juice survey
Cite as: McKean JD, O’Connor AM. Describing the Salmonella classification levels for low-volume production systems utilizing abattoir-based samples and classification stability over time. J Swine Health Prod 2009;17(4):198-203.
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