A European Union-wide baseline survey was carried out to determine the prevalence of Salmonella in commercial flocks of broilers with at least 5,000 birds in order to provide the scientific basis for setting a Community reduction target for Salmonella in broiler flocks of Gallus gallus. The sampling of the flocks took place between October 2005 and September 2006. Five faeces samples were taken from the flocks within 3 weeks before leaving for slaughter. A total of 6,325 holdings corresponding to 7,440 flocks with validated results were included in the survey analysis. The analysis of the Salmonella prevalence was carried out earlier and was published by the European Food Safety Authority on 30 March 2007 in part A report.
In a further analysis published in this part B report only few factors were found to be associated with Salmonella flock prevalence at the Community-level. The Community Salmonella flock prevalence varied significantly and importantly between months of sampling. The months found to be associated with higher flock prevalence were not consistently the same for different Salmonella serovars.
Flocks with younger broilers were associated with a higher risk of being S. Enteritidis positive, whereas broiler houses with a higher number of cycles of flocks per year were associated with higher flock prevalence for serovars other than S. Enteritidis and S. Infantis. The flock production type and the medication status were found to be associated with S. Infantis flock prevalence but since the Community S. Infantis prevalence was mostly driven by one Member State, these findings should be interpreted with caution.
S. Enteritidis was clearly the most frequently reported serovar in broiler flocks in the EU. S. Infantis, S. Mbandaka, S. Typhimurium, S. Hadar, S. Agona, S. Livingstone, S. Senftenberg, S. Montevideo, S. Tennessee and S. Virchow were also reported in between 8 to 12 MSs and should be regarded as important serovars of the broiler flock population.
The diversity of observed serovars differed greatly between MSs from a single serovar reported to more than 20 different serovars reported. Also the distribution of the serovars varied strongly amongst the MSs. Though 17 MSs reported S. Enteritidis, a formal spatial analysis identified two MSs as the most likely clusters for this serovar, whereas the most likely clusters for S. Typhimurium included three MSs.
The serovar distribution in broiler flocks and those reported in holdings with flocks of laying hen appeared to be similar in the EU. Similarities in Salmonella prevalence and serovar distributions were also found between broiler flocks and breeding flocks for broilers within the MSs, indicating that breeding flocks are likely to form an important source of Salmonella infections for the broiler flocks. Moreover, there was often a good agreement between the serovar and phage type distribution in human salmonellosis cases and in broiler flocks. These findings suggest that in the EU broiler meat is an important source of Salmonella infections in humans, although this importance is likely to differ between the MSs due to the varying Salmonella prevalence in broiler flocks.
The antimicrobial susceptibility testing information reported was not representative of the whole of the EU. The proportion of resistant isolates to third generation cephalosporins in the reporting MSs was very low, whereas two MSs reported the presence of S. Paratyphi B var. Java strains resistant to ceftiofur and to nalidixic acid. S. Enteritidis isolates were relatively susceptible to the tested antimicrobials, while resistance in S. Typhimurium was generally higher.
Since few risk factors were found to be associated with Salmonella flock prevalence at the Community-level, MSs are invited to carry out studies to identify the factors that put broiler flocks at risk of becoming infected with Salmonella at the national level. It is recommended that MSs are also encouraged to guarantee effective Salmonella control in breeding flocks for broilers in order to reduce and prevent the subsequent contamination of the broiler flocks. It is also further recommended that MSs serotype all Salmonella isolates originating from broiler flocks to enable evaluation of the public health importance of the findings.
Making the reporting on antimicrobial resistance and phage typing obligatory in future baseline studies would provide for more representative information.