Walking a thin line: Thinning broiler houses with Salmonella contaminated material

Salmonella Infantis and Salmonella Paratyphi B var. Java are important human pathogens that are mainly found on chicken meat and derivative products. Furthermore, both serovars are dominantly present in the Belgian broiler sector. In search of contamination routes in the sector, equipment used during partial depopulation or thinning was sampled at ten different broiler farms. All thinning materials, such as the trucks, crates and workwear of the catching crew were sampled before entering the broiler houses. To evaluate if the remaining birds became colonized by Salmonella strains introduced during thinning, the broiler houses were sampled twice using overshoes. Once immediately before thinning and approximately one week after thinning, immediately before final depopulation. The results show that during nine of the ten thinning events Salmonella was present on the equipment used. Especially the crates and loading surfaces of the trucks were frequently contaminated, 19.3 % (62/320) of the sampled crates and 50 % (11/22) of the sampled trucks were found contaminated with S. Infantis, Paratyphi B var. Java or Livingstone. The relative prevalences of S. Infantis, Java and Livingstone were, respectively, 31.3 %, 67.5 % and 1.3 %. Despite the presence of Salmonella during thinning, no cross-contamination to the remaining chickens was observed. A low abundance of Salmonella bacteria, a higher resistance of the older (five weeks), remaining chickens or a small sampling size can explain these results. Nevertheless, the results of this case report underscore the importance of appropriate biosecurity during thinning.