Koen De Reu and colleagues from the Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), and other Belgian institutions studied Salmonella in five poultry processing plants after cleaning and disinfection to better understand Salmonella contamination sources and transmission routes.

After cleaning and disinfection, samples from the slaughter and cutting lines were collected, as well as neck skin samples and thighs during slaughter of the first flock. In total, 680 swab and water samples were taken from the slaughter line before slaughter.

In all processing plants Salmonella was still isolated from the slaughter line before start of activities, notwithstanding cleaning and disinfection.

The prevalence of Salmonella in the plucking area was 10.4% (38/365), (hanging area: 5.0%, scalding tank: 5.8%, plucking machine: 17.0%); in the evisceration room, 1.5% (2/138); and in the cutting area, 2.0% (3/149), according to the researchers.

No Salmonella (0/28) was found in samples from the chilling line.

On neck skin samples taken from the various lines, Salmonella prevalence was 16.1% (48/299) after plucking, 16.0% (48/300) after evisceration, 23.3% (70/300) after chilling; on thighs, prevalence was 10.0% (24/240).

Nine Salmonella serotypes were identified, of which S. Infantis was the most common serovar (53.8%), especially in slaughterhouse A.

Two contamination causes were identified. First, although all flocks had an official Salmonella negative status, this was incorrect in one case, which led to an enormous contamination of the neck skins of the flock and the slaughter line.

Second, molecular typing revealed cross-contamination from flocks slaughtered one day prior to sampling. Salmonella was apparently not always eliminated by the cleaning and disinfection process and able to contaminate the carcasses of the first slaughtered flock.

The results of this study provide practical insights for poultry production to further improve their Salmonella control. Steps that can be taken include Salmonella status determination of flocks closer to the slaughter date, adapting cleaning and disinfection protocols especially for critical machinery, and better hygienically designed equipment.