National Microbiological Baseline Study in Broiler Chicken
December 2012 – December 2013

Discussion

Overall, 96% of 10,023 planned samples were collected along the broiler supply chain and tested for the presence and enumeration of two foodborne pathogens, Campylobacter and Salmonella, and one indicator organism of meat hygiene, generic E. coli. This high performance in sample collection and testing achieved during the entire study will allow inference of prevalence estimates to the target populations and an evaluation of seasonal variation of microorganisms in broiler chicken flocks, carcasses and parts at the chosen precision level in the study design.

The presence of Campylobacter and Salmonella on broiler chicken carcasses primarily originates from the intestinal carriage in the live birds. Both pathogens colonize the intestinal tracts of broiler chicken and can reach extremely high numbers in caecal content (Newell and Fearnley, 2003; FSANZ, 2010) The microbiota of the caecal contents of slaughtered broiler chickens is commonly used to evaluate the microbial status of flocks or farms (Arsenault et al., 2007; Guerin et al., 2007).The detection of Campylobacter- or Salmonella-positive broiler chicken lots at slaughter was performed by pooling and testing 20 intact caeca from individual birds of the same lot taken after the evisceration process. Any positive pooled caeca samples would primarily reflect the colonisation of lots of broiler chicken that have been raised in the same barn. Planned analysis of barn and producer identifiers will allow us to estimate and report on the prevalence of these pathogens at the flock and farm level. 

The national prevalence of Salmonella in broiler chicken lots processed in federally-registered establishments was 25.6% with provinces from eastern Canada showing the highest prevalence ranging from 28.9% to 34.3%. In contrast, the national prevalence of Campylobacter-colonised broiler chicken lots was 24.1% with the higher prevalence observed in the provinces of western Canada, especially in British Columbia at 41.3%. Differences in climatic conditions (Patrick et al., 2004; Jonsson et al., 2012) and/or farm-level factors (Arsenault et al., 2007; Guerin et al., 2007) influencing the risk of Campylobacter colonization of broilers flocks may explain the variation among provinces, but further research is needed to expand on these findings.

The prevalence of Campylobacter, Salmonella and generic E. coli were determined on whole chicken carcasses and parts processed in federally-registered establishments at the national scale and not by province. Sampling of whole carcasses occurred at post-chill similar to the previous 1997-98 MBS (CFIA, 2000). Parts, either SLBL breasts or SOBI thighs were collected as tray packs or directly from a bulk pack prior to packaging when tray packs were not produced. The prevalence of Campylobacter and Salmonella on chicken parts was found to be 1.4 and 1.8 times higher than those observed on whole carcasses, respectively. Cross-contamination events resulting from further processing and handling of parts may explain the differences in prevalence between these types of poultry products as was hypothesized by FSIS (2010a). In comparison with the 1997-98 MBS, the prevalence of Salmonella on whole carcasses significantly decreased from 21.1% to 16.9% (CFIA, 2000). This comparison should be made with caution as the detection methods for Salmonella were not the same and the difference in prevalence observed between the two studies does not provide an accurate measure of temporal trend. No testing for Campylobacter was performed during the previous Canadian MBS preventing comparison with the current study.

Similar types of raw chicken products were collected and tested from supermarket chains and independent grocers or butcher shops in the larger cities across Canada. Although a large proportion of retail chickens sold in supermarket chains are supplied by federally-registered establishments, approximately 20% of sampled chickens were purchased from independent grocers or butcher shops who may offer chicken products processed in provincially-inspected plants. The food retail outlets offer a variety of chicken meat products to consumers that could be processed in federal, provincial, or more rarely in a poultry establishment outside of Canada. These products could be pre-packaged in establishments or packaged in-store, of organic or conventional production, and/or further processed. In this study, all selected products were fresh and excluded products that were cooked, frozen, previously frozen, marinated or seasoned. The prevalence of Campylobacter and Salmonella on fresh retail chicken products was 41.8% (CI: 39.4% – 44.2%) and 29.0% (CI: 26.8% - 31.2%), respectively.

The prevalence of Campylobacter and Salmonella on fresh chicken parts was higher than in whole carcasses whether they were collected in abattoirs or retail food outlets. The concentration of Salmonella was generally low and not different within and between product types. In contrast, the concentration of Campylobacter on SLBL breasts was significantly lower than those found on whole carcasses and SOBI thighs. A large-scale retail study in the UK also showed that the concentration of Campylobacter was higher on parts with the skin-on compared to those with the skin-off (FSA, 2009).

This national MBS in broiler chicken provides current baseline estimates on the prevalence and concentration of Campylobacter and Salmonella at various stages along the broiler chicken meat supply chain. It is recognized that this is a snapshot in time and support for further/continued research may have to be pursued. This information is intended to be used as a science-based foundation by governments, industry and other stakeholders to inform the development of a risk management strategy for the control of Campylobacter and Salmonella in chicken produced in Canada. To achieve further reduction at processing or retail, a future strategy should consider the implementation of new interventions or mitigation measures along the supply chain from primary production to retail levels.

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