Moving Past Species Classifications for Risk-Based Approaches to Food Safety: Salmonella as a Case Study

Abstract

Classification of bacterial pathogens into species has traditionally been an essential prerequisite for many aspects of infection control and food safety. Consequently, control measures, regulations, industry specifications, and other guidance documents for foodborne pathogens typically specify a pathogen species (or genus) as target. For example, current Codex Alimentarius guidelines recommend absence of Salmonella in two 375 g samples for infant formula (FAO, 2020). For other ready-to-eat (RTE) foods, absence in smaller samples size (e.g., 25 g) is typically expected. However, there is increasing evidence for Salmonella, as well as other foodborne pathogens, that subgroups, serovars, and/or clonal groups within a given species may differ considerably in their ability to cause human disease. Importantly, there is emerging evidence that use of “sub-species” (or “sub-genus”) classification for defining food safety hazards may allow for more effective management of foodborne pathogens. The genus Salmonella, a pathogen where all members of the genus are considered a food safety hazard, represents one key foodborne pathogen where there is increasing evidence that subtypes differ considerably in their likelihood of causing human disease and where science-based subtype-specific and risk-based approaches of control may have a positive public health impact. There is clear evidence that certain Salmonella subtypes (e.g., certain subtypes within serovars Kentucky and Cerro) show reduced human virulence, while being frequently isolated from food animal species (specifically poultry and cattle) (Rodriguez-Rivera et al., 2014; Haley et al., 2016). Additionally, under the current approach of considering all Salmonella equally likely to cause human disease, limited progress has been made worldwide to reduce foodborne salmonellosis cases (Havelaar et al., 2015; Tack et al., 2020). In some situations, there are counterproductive incentives to prioritize control of highly frequent Salmonella strains with limited human public health relevance (e.g., through poultry vaccines targeting S. Kentucky) over control of less frequent Salmonella strains commonly linked to human salmonellosis cases. We outline a new paradigm for incorporating strain-specific assessment of human public health significance into regulations and control strategies, which we propose should be used to incentivize control of Salmonella subtypes with the greatest public health impact, with a focus on pre-harvest control in meat and poultry. This paradigm could subsequently be applied to other foodborne pathogens, such as Listeria monocytogenes.