Scientific Documents

Analysis of the baseline survey on the prevalence of Salmonella in slaughter pigs, in the EU, 2006-2007 - Part B: factors associated with Salmonella infection in lymph nodes, Salmonella surface contamination of carcasses, and the distribution of Salmonella serovars[1]

Report (1298 KB)

Annex I (448 KB)

A European Union-wide baseline survey was carried out to determine, at the point of slaughter, the prevalence of pigs infected with Salmonella, in order to provide the scientific basis for setting a Community reduction target for Salmonella in slaughter pigs. The sampling of slaughter pigs took place between October 2006 and September 2007. The pigs were randomly selected from those slaughterhouses that together accounted for 80% of the pigs slaughtered within each Member State. All participating Member States and Norway sampled ileocaecal lymph nodes from the selected slaughtered pigs. Moreover, 13 Member States additionally sampled the corresponding pigs’ carcasses by swabbing in order to appreciate the external contamination of the carcasses. A total of 19,159 slaughter pigs with validated results from the European Union and Norway were included in the survey analyses, corresponding to information on 19,025 lymph node samples (from 25 Member States and Norway) and 5,736 carcass swab samples (from 13 Member States).

The analysis of Salmonella prevalence was carried out earlier and was published by the European Food Safety Authority on 30 May 2008 in the Part A report. The Community observed prevalence of Salmonella-positive slaughter pigs was 10.3%, whereas data from the group of 13 Member States showed that the observed prevalence of carcasses contaminated with Salmonella was 8.3% overall. In both cases, prevalence varied among Member States.

In the risk factor analysis, an association between the prevalence of slaughter pigs infected with Salmonella in their lymph nodes and the frequency of Salmonella surface contamination of the pig carcasses was observed. A Salmonella infected pig was twice as likely to yield a Salmonella contaminated carcass. However, contaminated carcasses could also derive from uninfected pigs, suggesting potential for cross-contamination in the slaughterhouse environment. The risk of carcasses becoming contaminated with Salmonella varied significantly between slaughterhouses even when other associated factors, such as the prevalence of infected slaughter pigs, were accounted for. Moreover, in some slaughterhouses the risks of producing a contaminated carcass both from a Salmonella infected pig and from a non-infected pig were significantly higher than in some other slaughterhouses. This indicates that certain slaughterhouses are more capable of controlling and preventing Salmonella contamination than others.

The delay between sampling and the start of laboratory testing was found to have an impact on the likelihood of detecting Salmonella from the samples. The bacterium was most likely to be detected from lymph nodes and carcass swabs when the sample was tested 3-4 or 1-2 days after sampling, respectively. Also the probability of detecting Salmonella from a lymph node sample augmented when the weight of the sample increased.

At the European Union level, the carcasses were less at risk of being contaminated during the first months of the survey, October 2006 to March 2007, compared to the rest of the survey period, from April to September 2007.

The analyses also revealed that there is considerable variation between the significant factors associated with Salmonella infection in slaughter pig’s lymph nodes, or Salmonella carcass contamination, among Member States and also when compared to EU level.

A tendency towards Member State-specific clusters of Salmonella serovars was identified for Salmonella infection in slaughter pigs, and spatial distribution of serovars was very heterogeneous. S. Typhimurium and S. Derby were widespread and dominant in the Member States. However, S. Enteritidis was relatively prevalent in some eastern EU Member States.

The descriptive analysis of the serovar distribution supported the notion that pig meat contributes to human Salmonella infection. However, many serovars isolated from slaughter pigs in this survey are also common in other food producing animal species and food thereof, indicating that the potential for the contribution to human infections is shared between different sources.

It is recommended that Member States would consider the factors found to be associated with Salmonella infection in slaughter pigs and carcasses in this survey when they are designing their Salmonella control programmes for slaughter pigs. Control measures both at primary production and at slaughterhouse level should be included in the programmes. In particular sampling and testing procedures need standardisation to enhance sensitivity and comparability of monitoring results.

Member States and the EU pig meat industry are encouraged to develop and enhance Salmonella controls in primary production and at slaughterhouses in order to prevent and reduce the contamination of pig carcasses with Salmonella. Member States are also invited to perform further studies at national level to identify specifically the risk factors for Salmonella infection of slaughter pigs and surface contamination of carcasses.