Quantitative Microbiological Risk Assessment: Dealing with Biological Diversity

During the past 20 years, quantitative microbiological risk assessment (QRMA) for evaluating food safety issues has evolved from an object of academic curiosity to an established risk analysis sub-discipline. QMRA techniques are increasingly used by both industry and regulatory agencies to inform priority setting, the relative effectiveness of potential risk management options, the development of integrated food safety systems, and the impact of pathogenic/toxigenic microorganism of high-risk segments of the consuming public. The development of QMRA methods has been strongly influenced by earlier work in chemical risk assessments, as reflected in the adoption of the four component approach to risk assessments, i.e., hazard identification, hazard characterization, exposure assessment, and risk characterization. However, unlike many chemical risk assessments, the dramatic and often rapid changes in the levels of a pathogenic microorganism that can occur along a farm-to-fork food chain had to be a major focus of QRMA development. For example, a single cell of Salmonella can increase to billions per gram overnight, and then plummet back to a single cell after a 5-minute heating on the stove. Likewise, the susceptibility of the human population to pathogenic microorganism routinely varies from highly sensitive, immunocompromised individuals to others who are totally immune due prior exposures or vaccines. Likewise, the relative pathogenicity of individual species can vary substantially depending on the virulence determinants individual strains have acquired, and the mechanisms of disease among the various classes of foodborne pathogenic microorganisms. For example, dose-response relations for infectious and toxico-infectious agents are typically best described with non-threshold models, whereas toxigenic agents are better described with threshold models. Advances in QMRA helping find practical means for decreasing uncertainty by better understanding and describing the impact biodiversity on risk. This focus is also helping find new methods for addressing biodiversity issues associated with chemical and environmental risk assessments, particularly for carcinogens and mutagens.