Prevalence of a Salmonella subspecies diarizonae in Norwegian sheep herds.

We studied the prevalence of Salmonella enterica subspecies diarizonae serovar 61:k:1,5,(7) (S. IIIb 61:k:1,5,(7)) in 133 Norwegian sheep herds from throughout the country. We used a nested case-control study to identify major risk factors. Two pooled samples (one from lambs and one from adult sheep) were collected from each herd from (10 different) abattoirs. The regional prevalence varied from 0 to 45%, and was more prevalent in adults than in lambs. Sixteen of the 133 herds tested positive to S. IIIb 61:k:1,5,(7), and these positive herds were included in the questionnaire-based nested case-control part of the study. The controls were stratified according to abattoir. Above-median herd size, having white crossbreed sheep, and higher annual replacement percentage were the most evident risk factors.