Assessment of Salmonella spp, Typhimurium or Derby potential risk factors in Danish breeding pig holdings using multilevel approach

Abstract

Pork and products thereof are known important sources of Salmonella to humans with particular concern to S. Typhimurium and S. Derby. The purpose of this work is to present potential risk factors for Salmonella Derby or S. Typhimurium in feces in Danish breeding pig herds, using data from the EU baseline survey on prevalence of Salmonella in breeding pigs, 2008. Multi-level multivariable analysis including 2930 pens (12 variables) within 293 holdings (7 variables) was carried in SPSS version 22 using GLMM. Three outcomes were assessed, based on Salmonella positivity or negativity of the pens' fecal pools: one binomial (Salmonella positive or negative pool); two multinomial outcomes, one with S. Typhimurium positive or S. non-Typhimurium positive or Salmonella negative pools and the other with S. Derby positive or S. non-Derby positive or Salmonella negative pools. Potential risk factors (p<0.05) for Salmonella positivity were: total number of breeding pigs, boar replacement policy and type of feed; S. Typhimurium-dependent potential risk factors were boar replacement policy and type of feed; S. Derby-dependent potential risk factors were boar replacement policy, type of feed and source of feed. The results from our analysis for Salmonella spp are in line with the conclusions from the EFSA report at the EU-level. Differences are that fewer associations were found in Danish data, with the variable boar replacement policy being retained in all three final models. A similar association was found in Portugal, which was source of semen. Results from Denmark and Portugal retained potential similar associations but full comparability was not possible due to some differences in the statistical methodology. Serotype-specific risk factor investigation revealed different risk associations for S. Typhimurium in Portugal and Denmark. Serotype-specific risk associations for S. Typhimurium and S. Derby in Denmark showed some differences which will be discussed.