Food safety

About microbiological risk assessment (MRA) in food

What is MRA in food?

Concept of risk assessment

Risk assessment is a structured process for determining the risk associated with any type of hazard -biological, chemical, or physical-in a food. It has as its objective a characterization of the nature and likelihood of harm resulting from human exposure to agents in food. The characterization of risk typically contains both qualitative and quantitative information and is associated with a certain degree of scientific uncertainty.

There are four very distinct steps in the risk assessment process. The first step is hazard identification, which involves the collection, organization, and evaluation of all information pertaining to a pathogen or a nutrient. Second is hazard characterization, which determines the relationship between a pathogen and any adverse effects. Third is exposure assessment, which involves determining how much of pathogen might be ingested in a serving of food. The fourth, and last step, is risk characterization, which involves evaluating the risk and related information.

Applications of risk assessment

Risk assessment provides structured information that allows decision makers to identify interventions that can lead to public health improvement and provides a basis for them to use in weighing the options. These options include regulatory action when necessary, but also include a broad range of options such as voluntary activities and educational initiatives. Risk assessment also can be used to identify data gaps and target research that should have the greatest value in terms of public health impact.

Risk assessment will also help industry to develop more effective HACCP plans. For the future, risk assessments will help plants to scientifically develop HACCP plans. For instance, plants can use a risk assessment to help identify hazards that are reasonably likely to occur. The best information plants may have now is qualitative-for example, whether a hazard presents a high, medium, or low risk. The real benefit to this change is that a hazard would be defined in terms of the risk of an adverse human health consequence, rather than in terms of contamination of the food.

Risk assessments also play an important role in international trade by ensuring that countries establish food safety requirements that are scientifically sound and by providing a means for determining equivalent levels of public health protection between countries. Without a systematic assessment of risk assessment, countries may set requirements that are not related to food safety, and could create artificial barriers to trade. Recognizing the importance of this science-based approach to fair trade, the World Trade Organization requires each country's food safety measures to be based on risk assessment. The Codex Alimentarius Commission, which establishes international food safety standards, is now developing principles for using risk assessment in establish such standards.

Difficulties of microbiological risk assessment

Risk assessment has its roots in the concerns for toxic chemicals in food. While these assessments are based on toxicology and carcinogenity studies, their application to microbial pathogens* poses some significant difficulties. One difficulty, of course, relates to the fact that unlike chemical, environmental, or toxicological contaminants, bacteria can multiply as conditions change as food moves through the farm to table continuum. Fortunately, researchers are making progress in developing the predictive models and other tools that will meet the technical requirements for quantifying estimates of risk.

In addition to this technical difficulty, there are many data gaps that limit the precision necessary for quantitative risk assessments. For instance, there is little information to accurately estimate the relationship between the quantity of a biological agent and the frequency and magnitude of adverse human health effects, particularly as this might relate to susceptible sub-populations. There is also limited information on exposure assessment - the accounts of foods consumed by populations and their probable contamination.

*Including risk arising from the presence of bacterial, viral, protozoal, fungal organisms, or their metabolites in foods.

Methodology of microbiological risk assessment

Mathematical models are used to describe the introduction of pathogens into food, the replication of microbes in food over time, the destruction of microbes by heat treatment, the consumption of microbes in food, and subsequent illness. Both variability and uncertainty in the values used for input can be described by probability distributions. A probability distribution is a mathematical representation of the relative likelihood of a random variable taking on a specific value. Monte Carlo simulation of the model provides an estimate of level of human illness and the uncertainty associated with that estimate. Control strategies can be modelled in the same way and the cost and benefit (in terms of illness prevented) can be compared.